Down-integrate from google3.

50 files changed, 2328 insertions, 849 deletions

diff --git a/python/compatibility_tests/v2.5.0/tests/google/protobuf/internal/text_format_test.py b/python/compatibility_tests/v2.5.0/tests/google/protobuf/internal/text_format_test.py
index 8267cd2c..bc53e256 100755
--- a/python/compatibility_tests/v2.5.0/tests/google/protobuf/internal/text_format_test.py
+++ b/python/compatibility_tests/v2.5.0/tests/google/protobuf/internal/text_format_test.py
@@ -410,7 +410,8 @@ class TextFormatTest(unittest.TestCase):
     text = 'optional_nested_enum: BARR'
     self.assertRaisesWithMessage(
         text_format.ParseError,
-        ('1:23 : Enum type "protobuf_unittest.TestAllTypes.NestedEnum" '
+        ('1:23 : \'optional_nested_enum: BARR\': '
+         'Enum type "protobuf_unittest.TestAllTypes.NestedEnum" '
          'has no value named BARR.'),
         text_format.Merge, text, message)
 
@@ -418,7 +419,8 @@ class TextFormatTest(unittest.TestCase):
     text = 'optional_nested_enum: 100'
     self.assertRaisesWithMessage(
         text_format.ParseError,
-        ('1:23 : Enum type "protobuf_unittest.TestAllTypes.NestedEnum" '
+        ('1:23 : \'optional_nested_enum: 100\': '
+         'Enum type "protobuf_unittest.TestAllTypes.NestedEnum" '
          'has no value with number 100.'),
         text_format.Merge, text, message)
 
@@ -427,7 +429,8 @@ class TextFormatTest(unittest.TestCase):
     text = 'optional_int32: bork'
     self.assertRaisesWithMessage(
         text_format.ParseError,
-        ('1:17 : Couldn\'t parse integer: bork'),
+        ('1:17 : \'optional_int32: bork\': '
+         'Couldn\'t parse integer: bork'),
         text_format.Merge, text, message)
 
   def testMergeStringFieldUnescape(self):
diff --git a/python/google/protobuf/descriptor_database.py b/python/google/protobuf/descriptor_database.py
index 8b7715cd..a7616cbc 100644
--- a/python/google/protobuf/descriptor_database.py
+++ b/python/google/protobuf/descriptor_database.py
@@ -76,6 +76,9 @@ class DescriptorDatabase(object):
         self._AddSymbol(name, file_desc_proto)
     for enum in file_desc_proto.enum_type:
       self._AddSymbol(('.'.join((package, enum.name))), file_desc_proto)
+      for enum_value in enum.value:
+        self._file_desc_protos_by_symbol[
+            '.'.join((package, enum_value.name))] = file_desc_proto
     for extension in file_desc_proto.extension:
       self._AddSymbol(('.'.join((package, extension.name))), file_desc_proto)
     for service in file_desc_proto.service:
@@ -133,6 +136,14 @@ class DescriptorDatabase(object):
       top_level, _, _ = symbol.rpartition('.')
       return self._file_desc_protos_by_symbol[top_level]
 
+  def FindFileContainingExtension(self, extendee_name, extension_number):
+    # TODO(jieluo): implement this API.
+    return None
+
+  def FindAllExtensionNumbers(self, extendee_name):
+    # TODO(jieluo): implement this API.
+    return []
+
   def _AddSymbol(self, name, file_desc_proto):
     if name in self._file_desc_protos_by_symbol:
       warn_msg = ('Conflict register for file "' + file_desc_proto.name +
diff --git a/python/google/protobuf/descriptor_pool.py b/python/google/protobuf/descriptor_pool.py
index 8983f76f..42f7bcb5 100644
--- a/python/google/protobuf/descriptor_pool.py
+++ b/python/google/protobuf/descriptor_pool.py
@@ -131,33 +131,46 @@ class DescriptorPool(object):
     # TODO(jieluo): Remove _file_desc_by_toplevel_extension after
     # maybe year 2020 for compatibility issue (with 3.4.1 only).
     self._file_desc_by_toplevel_extension = {}
+    self._top_enum_values = {}
     # We store extensions in two two-level mappings: The first key is the
     # descriptor of the message being extended, the second key is the extension
     # full name or its tag number.
     self._extensions_by_name = collections.defaultdict(dict)
     self._extensions_by_number = collections.defaultdict(dict)
 
-  def _CheckConflictRegister(self, desc):
+  def _CheckConflictRegister(self, desc, desc_name, file_name):
     """Check if the descriptor name conflicts with another of the same name.
 
     Args:
-      desc: Descriptor of a message, enum, service or extension.
+      desc: Descriptor of a message, enum, service, extension or enum value.
+      desc_name: the full name of desc.
+      file_name: The file name of descriptor.
     """
-    desc_name = desc.full_name
     for register, descriptor_type in [
         (self._descriptors, descriptor.Descriptor),
         (self._enum_descriptors, descriptor.EnumDescriptor),
         (self._service_descriptors, descriptor.ServiceDescriptor),
-        (self._toplevel_extensions, descriptor.FieldDescriptor)]:
+        (self._toplevel_extensions, descriptor.FieldDescriptor),
+        (self._top_enum_values, descriptor.EnumValueDescriptor)]:
       if desc_name in register:
-        file_name = register[desc_name].file.name
+        old_desc = register[desc_name]
+        if isinstance(old_desc, descriptor.EnumValueDescriptor):
+          old_file = old_desc.type.file.name
+        else:
+          old_file = old_desc.file.name
+
         if not isinstance(desc, descriptor_type) or (
-            file_name != desc.file.name):
-          warn_msg = ('Conflict register for file "' + desc.file.name +
+            old_file != file_name):
+          warn_msg = ('Conflict register for file "' + file_name +
                       '": ' + desc_name +
                       ' is already defined in file "' +
-                      file_name + '"')
+                      old_file + '"')
+          if isinstance(desc, descriptor.EnumValueDescriptor):
+            warn_msg += ('\nNote: enum values appear as '
+                         'siblings of the enum type instead of '
+                         'children of it.')
           warnings.warn(warn_msg, RuntimeWarning)
+
         return
 
   def Add(self, file_desc_proto):
@@ -196,7 +209,7 @@ class DescriptorPool(object):
     if not isinstance(desc, descriptor.Descriptor):
       raise TypeError('Expected instance of descriptor.Descriptor.')
 
-    self._CheckConflictRegister(desc)
+    self._CheckConflictRegister(desc, desc.full_name, desc.file.name)
 
     self._descriptors[desc.full_name] = desc
     self._AddFileDescriptor(desc.file)
@@ -213,8 +226,26 @@ class DescriptorPool(object):
     if not isinstance(enum_desc, descriptor.EnumDescriptor):
       raise TypeError('Expected instance of descriptor.EnumDescriptor.')
 
-    self._CheckConflictRegister(enum_desc)
+    file_name = enum_desc.file.name
+    self._CheckConflictRegister(enum_desc, enum_desc.full_name, file_name)
     self._enum_descriptors[enum_desc.full_name] = enum_desc
+
+    # Top enum values need to be indexed.
+    # Count the number of dots to see whether the enum is toplevel or nested
+    # in a message. We cannot use enum_desc.containing_type at this stage.
+    if enum_desc.file.package:
+      top_level = (enum_desc.full_name.count('.')
+                   - enum_desc.file.package.count('.') == 1)
+    else:
+      top_level = enum_desc.full_name.count('.') == 0
+    if top_level:
+      file_name = enum_desc.file.name
+      package = enum_desc.file.package
+      for enum_value in enum_desc.values:
+        full_name = _NormalizeFullyQualifiedName(
+            '.'.join((package, enum_value.name)))
+        self._CheckConflictRegister(enum_value, full_name, file_name)
+        self._top_enum_values[full_name] = enum_value
     self._AddFileDescriptor(enum_desc.file)
 
   def AddServiceDescriptor(self, service_desc):
@@ -227,7 +258,8 @@ class DescriptorPool(object):
     if not isinstance(service_desc, descriptor.ServiceDescriptor):
       raise TypeError('Expected instance of descriptor.ServiceDescriptor.')
 
-    self._CheckConflictRegister(service_desc)
+    self._CheckConflictRegister(service_desc, service_desc.full_name,
+                                service_desc.file.name)
     self._service_descriptors[service_desc.full_name] = service_desc
 
   def AddExtensionDescriptor(self, extension):
@@ -247,7 +279,6 @@ class DescriptorPool(object):
       raise TypeError('Expected an extension descriptor.')
 
     if extension.extension_scope is None:
-      self._CheckConflictRegister(extension)
       self._toplevel_extensions[extension.full_name] = extension
 
     try:
@@ -349,6 +380,30 @@ class DescriptorPool(object):
 
     symbol = _NormalizeFullyQualifiedName(symbol)
     try:
+      return self._InternalFindFileContainingSymbol(symbol)
+    except KeyError:
+      pass
+
+    try:
+      # Try fallback database. Build and find again if possible.
+      self._FindFileContainingSymbolInDb(symbol)
+      return self._InternalFindFileContainingSymbol(symbol)
+    except KeyError:
+      raise KeyError('Cannot find a file containing %s' % symbol)
+
+  def _InternalFindFileContainingSymbol(self, symbol):
+    """Gets the already built FileDescriptor containing the specified symbol.
+
+    Args:
+      symbol: The name of the symbol to search for.
+
+    Returns:
+      A FileDescriptor that contains the specified symbol.
+
+    Raises:
+      KeyError: if the file cannot be found in the pool.
+    """
+    try:
       return self._descriptors[symbol].file
     except KeyError:
       pass
@@ -364,7 +419,7 @@ class DescriptorPool(object):
       pass
 
     try:
-      return self._FindFileContainingSymbolInDb(symbol)
+      return self._top_enum_values[symbol].type.file
     except KeyError:
       pass
 
@@ -373,13 +428,15 @@ class DescriptorPool(object):
     except KeyError:
       pass
 
-    # Try nested extensions inside a message.
-    message_name, _, extension_name = symbol.rpartition('.')
+    # Try fields, enum values and nested extensions inside a message.
+    top_name, _, sub_name = symbol.rpartition('.')
     try:
-      message = self.FindMessageTypeByName(message_name)
-      assert message.extensions_by_name[extension_name]
+      message = self.FindMessageTypeByName(top_name)
+      assert (sub_name in message.extensions_by_name or
+              sub_name in message.fields_by_name or
+              sub_name in message.enum_values_by_name)
       return message.file
-    except KeyError:
+    except (KeyError, AssertionError):
       raise KeyError('Cannot find a file containing %s' % symbol)
 
   def FindMessageTypeByName(self, full_name):
@@ -499,7 +556,11 @@ class DescriptorPool(object):
       KeyError: when no extension with the given number is known for the
         specified message.
     """
-    return self._extensions_by_number[message_descriptor][number]
+    try:
+      return self._extensions_by_number[message_descriptor][number]
+    except KeyError:
+      self._TryLoadExtensionFromDB(message_descriptor, number)
+      return self._extensions_by_number[message_descriptor][number]
 
   def FindAllExtensions(self, message_descriptor):
     """Gets all the known extension of a given message.
@@ -513,8 +574,57 @@ class DescriptorPool(object):
     Returns:
       A list of FieldDescriptor describing the extensions.
     """
+    # Fallback to descriptor db if FindAllExtensionNumbers is provided.
+    if self._descriptor_db and hasattr(
+        self._descriptor_db, 'FindAllExtensionNumbers'):
+      full_name = message_descriptor.full_name
+      all_numbers = self._descriptor_db.FindAllExtensionNumbers(full_name)
+      for number in all_numbers:
+        if number in self._extensions_by_number[message_descriptor]:
+          continue
+        self._TryLoadExtensionFromDB(message_descriptor, number)
+
     return list(self._extensions_by_number[message_descriptor].values())
 
+  def _TryLoadExtensionFromDB(self, message_descriptor, number):
+    """Try to Load extensions from decriptor db.
+
+    Args:
+      message_descriptor: descriptor of the extended message.
+      number: the extension number that needs to be loaded.
+    """
+    if not self._descriptor_db:
+      return
+    # Only supported when FindFileContainingExtension is provided.
+    if not hasattr(
+        self._descriptor_db, 'FindFileContainingExtension'):
+      return
+
+    full_name = message_descriptor.full_name
+    file_proto = self._descriptor_db.FindFileContainingExtension(
+        full_name, number)
+
+    if file_proto is None:
+      return
+
+    try:
+      file_desc = self._ConvertFileProtoToFileDescriptor(file_proto)
+      for extension in file_desc.extensions_by_name.values():
+        self._extensions_by_number[extension.containing_type][
+            extension.number] = extension
+        self._extensions_by_name[extension.containing_type][
+            extension.full_name] = extension
+      for message_type in file_desc.message_types_by_name.values():
+        for extension in message_type.extensions:
+          self._extensions_by_number[extension.containing_type][
+              extension.number] = extension
+          self._extensions_by_name[extension.containing_type][
+              extension.full_name] = extension
+    except:
+      warn_msg = ('Unable to load proto file %s for extension number %d.' %
+                  (file_proto.name, number))
+      warnings.warn(warn_msg, RuntimeWarning)
+
   def FindServiceByName(self, full_name):
     """Loads the named service descriptor from the pool.
 
@@ -532,6 +642,23 @@ class DescriptorPool(object):
       self._FindFileContainingSymbolInDb(full_name)
     return self._service_descriptors[full_name]
 
+  def FindMethodByName(self, full_name):
+    """Loads the named service method descriptor from the pool.
+
+    Args:
+      full_name: The full name of the method descriptor to load.
+
+    Returns:
+      The method descriptor for the service method.
+
+    Raises:
+      KeyError: if the method cannot be found in the pool.
+    """
+    full_name = _NormalizeFullyQualifiedName(full_name)
+    service_name, _, method_name = full_name.rpartition('.')
+    service_descriptor = self.FindServiceByName(service_name)
+    return service_descriptor.methods_by_name[method_name]
+
   def _FindFileContainingSymbolInDb(self, symbol):
     """Finds the file in descriptor DB containing the specified symbol.
 
@@ -567,7 +694,6 @@ class DescriptorPool(object):
     Returns:
       A FileDescriptor matching the passed in proto.
     """
-
     if file_proto.name not in self._file_descriptors:
       built_deps = list(self._GetDeps(file_proto.dependency))
       direct_deps = [self.FindFileByName(n) for n in file_proto.dependency]
@@ -604,7 +730,7 @@ class DescriptorPool(object):
       for enum_type in file_proto.enum_type:
         file_descriptor.enum_types_by_name[enum_type.name] = (
             self._ConvertEnumDescriptor(enum_type, file_proto.package,
-                                        file_descriptor, None, scope))
+                                        file_descriptor, None, scope, True))
 
       for index, extension_proto in enumerate(file_proto.extension):
         extension_desc = self._MakeFieldDescriptor(
@@ -616,6 +742,8 @@ class DescriptorPool(object):
                            file_descriptor.package, scope)
         file_descriptor.extensions_by_name[extension_desc.name] = (
             extension_desc)
+        self._file_desc_by_toplevel_extension[extension_desc.full_name] = (
+            file_descriptor)
 
       for desc_proto in file_proto.message_type:
         self._SetAllFieldTypes(file_proto.package, desc_proto, scope)
@@ -673,7 +801,8 @@ class DescriptorPool(object):
             nested, desc_name, file_desc, scope, syntax)
         for nested in desc_proto.nested_type]
     enums = [
-        self._ConvertEnumDescriptor(enum, desc_name, file_desc, None, scope)
+        self._ConvertEnumDescriptor(enum, desc_name, file_desc, None,
+                                    scope, False)
         for enum in desc_proto.enum_type]
     fields = [self._MakeFieldDescriptor(field, desc_name, index, file_desc)
               for index, field in enumerate(desc_proto.field)]
@@ -718,12 +847,12 @@ class DescriptorPool(object):
         fields[field_index].containing_oneof = oneofs[oneof_index]
 
     scope[_PrefixWithDot(desc_name)] = desc
-    self._CheckConflictRegister(desc)
+    self._CheckConflictRegister(desc, desc.full_name, desc.file.name)
     self._descriptors[desc_name] = desc
     return desc
 
   def _ConvertEnumDescriptor(self, enum_proto, package=None, file_desc=None,
-                             containing_type=None, scope=None):
+                             containing_type=None, scope=None, top_level=False):
     """Make a protobuf EnumDescriptor given an EnumDescriptorProto protobuf.
 
     Args:
@@ -732,6 +861,8 @@ class DescriptorPool(object):
       file_desc: The file containing the enum descriptor.
       containing_type: The type containing this enum.
       scope: Scope containing available types.
+      top_level: If True, the enum is a top level symbol. If False, the enum
+          is defined inside a message.
 
     Returns:
       The added descriptor
@@ -757,8 +888,17 @@ class DescriptorPool(object):
                                      containing_type=containing_type,
                                      options=_OptionsOrNone(enum_proto))
     scope['.%s' % enum_name] = desc
-    self._CheckConflictRegister(desc)
+    self._CheckConflictRegister(desc, desc.full_name, desc.file.name)
     self._enum_descriptors[enum_name] = desc
+
+    # Add top level enum values.
+    if top_level:
+      for value in values:
+        full_name = _NormalizeFullyQualifiedName(
+            '.'.join((package, value.name)))
+        self._CheckConflictRegister(value, full_name, file_name)
+        self._top_enum_values[full_name] = value
+
     return desc
 
   def _MakeFieldDescriptor(self, field_proto, message_name, index,
@@ -885,6 +1025,8 @@ class DescriptorPool(object):
       elif field_proto.type == descriptor.FieldDescriptor.TYPE_BYTES:
         field_desc.default_value = text_encoding.CUnescape(
             field_proto.default_value)
+      elif field_proto.type == descriptor.FieldDescriptor.TYPE_MESSAGE:
+        field_desc.default_value = None
       else:
         # All other types are of the "int" type.
         field_desc.default_value = int(field_proto.default_value)
@@ -901,6 +1043,8 @@ class DescriptorPool(object):
         field_desc.default_value = field_desc.enum_type.values[0].number
       elif field_proto.type == descriptor.FieldDescriptor.TYPE_BYTES:
         field_desc.default_value = b''
+      elif field_proto.type == descriptor.FieldDescriptor.TYPE_MESSAGE:
+        field_desc.default_value = None
       else:
         # All other types are of the "int" type.
         field_desc.default_value = 0
@@ -954,7 +1098,7 @@ class DescriptorPool(object):
                                         methods=methods,
                                         options=_OptionsOrNone(service_proto),
                                         file=file_desc)
-    self._CheckConflictRegister(desc)
+    self._CheckConflictRegister(desc, desc.full_name, desc.file.name)
     self._service_descriptors[service_name] = desc
     return desc
 
diff --git a/python/google/protobuf/internal/__init__.py b/python/google/protobuf/internal/__init__.py
index e69de29b..7d2e571a 100755
--- a/python/google/protobuf/internal/__init__.py
+++ b/python/google/protobuf/internal/__init__.py
@@ -0,0 +1,30 @@
+# Protocol Buffers - Google's data interchange format
+# Copyright 2008 Google Inc.  All rights reserved.
+# https://developers.google.com/protocol-buffers/
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
diff --git a/python/google/protobuf/internal/api_implementation.py b/python/google/protobuf/internal/api_implementation.py
index ab9e7812..23cc2c0a 100755
--- a/python/google/protobuf/internal/api_implementation.py
+++ b/python/google/protobuf/internal/api_implementation.py
@@ -145,29 +145,3 @@ def Version():
 # For internal use only
 def IsPythonDefaultSerializationDeterministic():
   return _python_deterministic_proto_serialization
-
-# DO NOT USE: For migration and testing only. Will be removed when Proto3
-# defaults to preserve unknowns.
-if _implementation_type == 'cpp':
-  try:
-    # pylint: disable=g-import-not-at-top
-    from google.protobuf.pyext import _message
-
-    def GetPythonProto3PreserveUnknownsDefault():
-      return _message.GetPythonProto3PreserveUnknownsDefault()
-
-    def SetPythonProto3PreserveUnknownsDefault(preserve):
-      _message.SetPythonProto3PreserveUnknownsDefault(preserve)
-  except ImportError:
-    # Unrecognized cpp implementation. Skipping the unknown fields APIs.
-    pass
-else:
-  _python_proto3_preserve_unknowns_default = True
-
-  def GetPythonProto3PreserveUnknownsDefault():
-    return _python_proto3_preserve_unknowns_default
-
-  def SetPythonProto3PreserveUnknownsDefault(preserve):
-    global _python_proto3_preserve_unknowns_default
-    _python_proto3_preserve_unknowns_default = preserve
-
diff --git a/python/google/protobuf/internal/containers.py b/python/google/protobuf/internal/containers.py
index c6a3692a..182cac99 100755
--- a/python/google/protobuf/internal/containers.py
+++ b/python/google/protobuf/internal/containers.py
@@ -628,3 +628,130 @@ class MessageMap(MutableMapping):
 
   def GetEntryClass(self):
     return self._entry_descriptor._concrete_class
+
+
+class _UnknownField(object):
+
+  """A parsed unknown field."""
+
+  # Disallows assignment to other attributes.
+  __slots__ = ['_field_number', '_wire_type', '_data']
+
+  def __init__(self, field_number, wire_type, data):
+    self._field_number = field_number
+    self._wire_type = wire_type
+    self._data = data
+    return
+
+  def __lt__(self, other):
+    # pylint: disable=protected-access
+    return self._field_number < other._field_number
+
+  def __eq__(self, other):
+    if self is other:
+      return True
+    # pylint: disable=protected-access
+    return (self._field_number == other._field_number and
+            self._wire_type == other._wire_type and
+            self._data == other._data)
+
+
+class UnknownFieldRef(object):
+
+  def __init__(self, parent, index):
+    self._parent = parent
+    self._index = index
+    return
+
+  def _check_valid(self):
+    if not self._parent:
+      raise ValueError('UnknownField does not exist. '
+                       'The parent message might be cleared.')
+    if self._index >= len(self._parent):
+      raise ValueError('UnknownField does not exist. '
+                       'The parent message might be cleared.')
+
+  @property
+  def field_number(self):
+    self._check_valid()
+    # pylint: disable=protected-access
+    return self._parent._internal_get(self._index)._field_number
+
+  @property
+  def wire_type(self):
+    self._check_valid()
+    # pylint: disable=protected-access
+    return self._parent._internal_get(self._index)._wire_type
+
+  @property
+  def data(self):
+    self._check_valid()
+    # pylint: disable=protected-access
+    return self._parent._internal_get(self._index)._data
+
+
+class UnknownFieldSet(object):
+
+  """UnknownField container"""
+
+  # Disallows assignment to other attributes.
+  __slots__ = ['_values']
+
+  def __init__(self):
+    self._values = []
+
+  def __getitem__(self, index):
+    if self._values is None:
+      raise ValueError('UnknownFields does not exist. '
+                       'The parent message might be cleared.')
+    size = len(self._values)
+    if index < 0:
+      index += size
+    if index < 0 or index >= size:
+      raise IndexError('index %d out of range'.index)
+
+    return UnknownFieldRef(self, index)
+
+  def _internal_get(self, index):
+    return self._values[index]
+
+  def __len__(self):
+    if self._values is None:
+      raise ValueError('UnknownFields does not exist. '
+                       'The parent message might be cleared.')
+    return len(self._values)
+
+  def _add(self, field_number, wire_type, data):
+    unknown_field = _UnknownField(field_number, wire_type, data)
+    self._values.append(unknown_field)
+    return unknown_field
+
+  def __iter__(self):
+    for i in range(len(self)):
+      yield UnknownFieldRef(self, i)
+
+  def _extend(self, other):
+    if other is None:
+      return
+    # pylint: disable=protected-access
+    self._values.extend(other._values)
+
+  def __eq__(self, other):
+    if self is other:
+      return True
+    # Sort unknown fields because their order shouldn't
+    # affect equality test.
+    values = list(self._values)
+    if other is None:
+      return not values
+    values.sort()
+    # pylint: disable=protected-access
+    other_values = sorted(other._values)
+    return values == other_values
+
+  def _clear(self):
+    for value in self._values:
+      # pylint: disable=protected-access
+      if isinstance(value._data, UnknownFieldSet):
+        value._data._clear()  # pylint: disable=protected-access
+    self._values = None
diff --git a/python/google/protobuf/internal/decoder.py b/python/google/protobuf/internal/decoder.py
index 52b64915..938f6293 100755
--- a/python/google/protobuf/internal/decoder.py
+++ b/python/google/protobuf/internal/decoder.py
@@ -86,7 +86,11 @@ import six
 
 if six.PY3:
   long = int
+else:
+  import re    # pylint: disable=g-import-not-at-top
+  _SURROGATE_PATTERN = re.compile(six.u(r'[\ud800-\udfff]'))
 
+from google.protobuf.internal import containers
 from google.protobuf.internal import encoder
 from google.protobuf.internal import wire_format
 from google.protobuf import message
@@ -167,7 +171,7 @@ _DecodeSignedVarint32 = _SignedVarintDecoder(32, int)
 
 
 def ReadTag(buffer, pos):
-  """Read a tag from the buffer, and return a (tag_bytes, new_pos) tuple.
+  """Read a tag from the memoryview, and return a (tag_bytes, new_pos) tuple.
 
   We return the raw bytes of the tag rather than decoding them.  The raw
   bytes can then be used to look up the proper decoder.  This effectively allows
@@ -175,13 +179,21 @@ def ReadTag(buffer, pos):
   for work that is done in C (searching for a byte string in a hash table).
   In a low-level language it would be much cheaper to decode the varint and
   use that, but not in Python.
-  """
 
+  Args:
+    buffer: memoryview object of the encoded bytes
+    pos: int of the current position to start from
+
+  Returns:
+    Tuple[bytes, int] of the tag data and new position.
+  """
   start = pos
   while six.indexbytes(buffer, pos) & 0x80:
     pos += 1
   pos += 1
-  return (six.binary_type(buffer[start:pos]), pos)
+
+  tag_bytes = buffer[start:pos].tobytes()
+  return tag_bytes, pos
 
 
 # --------------------------------------------------------------------
@@ -295,10 +307,20 @@ def _FloatDecoder():
   local_unpack = struct.unpack
 
   def InnerDecode(buffer, pos):
+    """Decode serialized float to a float and new position.
+
+    Args:
+      buffer: memoryview of the serialized bytes
+      pos: int, position in the memory view to start at.
+
+    Returns:
+      Tuple[float, int] of the deserialized float value and new position
+      in the serialized data.
+    """
     # We expect a 32-bit value in little-endian byte order.  Bit 1 is the sign
     # bit, bits 2-9 represent the exponent, and bits 10-32 are the significand.
     new_pos = pos + 4
-    float_bytes = buffer[pos:new_pos]
+    float_bytes = buffer[pos:new_pos].tobytes()
 
     # If this value has all its exponent bits set, then it's non-finite.
     # In Python 2.4, struct.unpack will convert it to a finite 64-bit value.
@@ -329,10 +351,20 @@ def _DoubleDecoder():
   local_unpack = struct.unpack
 
   def InnerDecode(buffer, pos):
+    """Decode serialized double to a double and new position.
+
+    Args:
+      buffer: memoryview of the serialized bytes.
+      pos: int, position in the memory view to start at.
+
+    Returns:
+      Tuple[float, int] of the decoded double value and new position
+      in the serialized data.
+    """
     # We expect a 64-bit value in little-endian byte order.  Bit 1 is the sign
     # bit, bits 2-12 represent the exponent, and bits 13-64 are the significand.
     new_pos = pos + 8
-    double_bytes = buffer[pos:new_pos]
+    double_bytes = buffer[pos:new_pos].tobytes()
 
     # If this value has all its exponent bits set and at least one significand
     # bit set, it's not a number.  In Python 2.4, struct.unpack will treat it
@@ -355,6 +387,18 @@ def EnumDecoder(field_number, is_repeated, is_packed, key, new_default):
   if is_packed:
     local_DecodeVarint = _DecodeVarint
     def DecodePackedField(buffer, pos, end, message, field_dict):
+      """Decode serialized packed enum to its value and a new position.
+
+      Args:
+        buffer: memoryview of the serialized bytes.
+        pos: int, position in the memory view to start at.
+        end: int, end position of serialized data
+        message: Message object to store unknown fields in
+        field_dict: Map[Descriptor, Any] to store decoded values in.
+
+      Returns:
+        int, new position in serialized data.
+      """
       value = field_dict.get(key)
       if value is None:
         value = field_dict.setdefault(key, new_default(message))
@@ -365,6 +409,7 @@ def EnumDecoder(field_number, is_repeated, is_packed, key, new_default):
       while pos < endpoint:
         value_start_pos = pos
         (element, pos) = _DecodeSignedVarint32(buffer, pos)
+        # pylint: disable=protected-access
         if element in enum_type.values_by_number:
           value.append(element)
         else:
@@ -372,8 +417,10 @@ def EnumDecoder(field_number, is_repeated, is_packed, key, new_default):
             message._unknown_fields = []
           tag_bytes = encoder.TagBytes(field_number,
                                        wire_format.WIRETYPE_VARINT)
+
           message._unknown_fields.append(
-              (tag_bytes, buffer[value_start_pos:pos]))
+              (tag_bytes, buffer[value_start_pos:pos].tobytes()))
+          # pylint: enable=protected-access
       if pos > endpoint:
         if element in enum_type.values_by_number:
           del value[-1]   # Discard corrupt value.
@@ -386,18 +433,32 @@ def EnumDecoder(field_number, is_repeated, is_packed, key, new_default):
     tag_bytes = encoder.TagBytes(field_number, wire_format.WIRETYPE_VARINT)
     tag_len = len(tag_bytes)
     def DecodeRepeatedField(buffer, pos, end, message, field_dict):
+      """Decode serialized repeated enum to its value and a new position.
+
+      Args:
+        buffer: memoryview of the serialized bytes.
+        pos: int, position in the memory view to start at.
+        end: int, end position of serialized data
+        message: Message object to store unknown fields in
+        field_dict: Map[Descriptor, Any] to store decoded values in.
+
+      Returns:
+        int, new position in serialized data.
+      """
       value = field_dict.get(key)
       if value is None:
         value = field_dict.setdefault(key, new_default(message))
       while 1:
         (element, new_pos) = _DecodeSignedVarint32(buffer, pos)
+        # pylint: disable=protected-access
         if element in enum_type.values_by_number:
           value.append(element)
         else:
           if not message._unknown_fields:
             message._unknown_fields = []
           message._unknown_fields.append(
-              (tag_bytes, buffer[pos:new_pos]))
+              (tag_bytes, buffer[pos:new_pos].tobytes()))
+          # pylint: enable=protected-access
         # Predict that the next tag is another copy of the same repeated
         # field.
         pos = new_pos + tag_len
@@ -409,10 +470,23 @@ def EnumDecoder(field_number, is_repeated, is_packed, key, new_default):
     return DecodeRepeatedField
   else:
     def DecodeField(buffer, pos, end, message, field_dict):
+      """Decode serialized repeated enum to its value and a new position.
+
+      Args:
+        buffer: memoryview of the serialized bytes.
+        pos: int, position in the memory view to start at.
+        end: int, end position of serialized data
+        message: Message object to store unknown fields in
+        field_dict: Map[Descriptor, Any] to store decoded values in.
+
+      Returns:
+        int, new position in serialized data.
+      """
       value_start_pos = pos
       (enum_value, pos) = _DecodeSignedVarint32(buffer, pos)
       if pos > end:
         raise _DecodeError('Truncated message.')
+      # pylint: disable=protected-access
       if enum_value in enum_type.values_by_number:
         field_dict[key] = enum_value
       else:
@@ -421,7 +495,8 @@ def EnumDecoder(field_number, is_repeated, is_packed, key, new_default):
         tag_bytes = encoder.TagBytes(field_number,
                                      wire_format.WIRETYPE_VARINT)
         message._unknown_fields.append(
-          (tag_bytes, buffer[value_start_pos:pos]))
+            (tag_bytes, buffer[value_start_pos:pos].tobytes()))
+        # pylint: enable=protected-access
       return pos
     return DecodeField
 
@@ -458,20 +533,33 @@ BoolDecoder = _ModifiedDecoder(
     wire_format.WIRETYPE_VARINT, _DecodeVarint, bool)
 
 
-def StringDecoder(field_number, is_repeated, is_packed, key, new_default):
+def StringDecoder(field_number, is_repeated, is_packed, key, new_default,
+                  is_strict_utf8=False):
   """Returns a decoder for a string field."""
 
   local_DecodeVarint = _DecodeVarint
   local_unicode = six.text_type
 
-  def _ConvertToUnicode(byte_str):
+  def _ConvertToUnicode(memview):
+    """Convert byte to unicode."""
+    byte_str = memview.tobytes()
     try:
-      return local_unicode(byte_str, 'utf-8')
+      value = local_unicode(byte_str, 'utf-8')
     except UnicodeDecodeError as e:
       # add more information to the error message and re-raise it.
       e.reason = '%s in field: %s' % (e, key.full_name)
       raise
 
+    if is_strict_utf8 and six.PY2:
+      if _SURROGATE_PATTERN.search(value):
+        reason = ('String field %s contains invalid UTF-8 data when parsing'
+                  'a protocol buffer: surrogates not allowed. Use'
+                  'the bytes type if you intend to send raw bytes.') % (
+                      key.full_name)
+        raise message.DecodeError(reason)
+
+    return value
+
   assert not is_packed
   if is_repeated:
     tag_bytes = encoder.TagBytes(field_number,
@@ -523,7 +611,7 @@ def BytesDecoder(field_number, is_repeated, is_packed, key, new_default):
         new_pos = pos + size
         if new_pos > end:
           raise _DecodeError('Truncated string.')
-        value.append(buffer[pos:new_pos])
+        value.append(buffer[pos:new_pos].tobytes())
         # Predict that the next tag is another copy of the same repeated field.
         pos = new_pos + tag_len
         if buffer[new_pos:pos] != tag_bytes or new_pos == end:
@@ -536,7 +624,7 @@ def BytesDecoder(field_number, is_repeated, is_packed, key, new_default):
       new_pos = pos + size
       if new_pos > end:
         raise _DecodeError('Truncated string.')
-      field_dict[key] = buffer[pos:new_pos]
+      field_dict[key] = buffer[pos:new_pos].tobytes()
       return new_pos
     return DecodeField
 
@@ -665,6 +753,18 @@ def MessageSetItemDecoder(descriptor):
   local_SkipField = SkipField
 
   def DecodeItem(buffer, pos, end, message, field_dict):
+    """Decode serialized message set to its value and new position.
+
+    Args:
+      buffer: memoryview of the serialized bytes.
+      pos: int, position in the memory view to start at.
+      end: int, end position of serialized data
+      message: Message object to store unknown fields in
+      field_dict: Map[Descriptor, Any] to store decoded values in.
+
+    Returns:
+      int, new position in serialized data.
+    """
     message_set_item_start = pos
     type_id = -1
     message_start = -1
@@ -695,6 +795,7 @@ def MessageSetItemDecoder(descriptor):
       raise _DecodeError('MessageSet item missing message.')
 
     extension = message.Extensions._FindExtensionByNumber(type_id)
+    # pylint: disable=protected-access
     if extension is not None:
       value = field_dict.get(extension)
       if value is None:
@@ -707,8 +808,9 @@ def MessageSetItemDecoder(descriptor):
     else:
       if not message._unknown_fields:
         message._unknown_fields = []
-      message._unknown_fields.append((MESSAGE_SET_ITEM_TAG,
-                                      buffer[message_set_item_start:pos]))
+      message._unknown_fields.append(
+          (MESSAGE_SET_ITEM_TAG, buffer[message_set_item_start:pos].tobytes()))
+      # pylint: enable=protected-access
 
     return pos
 
@@ -767,7 +869,7 @@ def _SkipVarint(buffer, pos, end):
   # Previously ord(buffer[pos]) raised IndexError when pos is out of range.
   # With this code, ord(b'') raises TypeError.  Both are handled in
   # python_message.py to generate a 'Truncated message' error.
-  while ord(buffer[pos:pos+1]) & 0x80:
+  while ord(buffer[pos:pos+1].tobytes()) & 0x80:
     pos += 1
   pos += 1
   if pos > end:
@@ -782,6 +884,13 @@ def _SkipFixed64(buffer, pos, end):
     raise _DecodeError('Truncated message.')
   return pos
 
+
+def _DecodeFixed64(buffer, pos):
+  """Decode a fixed64."""
+  new_pos = pos + 8
+  return (struct.unpack('<Q', buffer[pos:new_pos])[0], new_pos)
+
+
 def _SkipLengthDelimited(buffer, pos, end):
   """Skip a length-delimited value.  Returns the new position."""
 
@@ -791,6 +900,7 @@ def _SkipLengthDelimited(buffer, pos, end):
     raise _DecodeError('Truncated message.')
   return pos
 
+
 def _SkipGroup(buffer, pos, end):
   """Skip sub-group.  Returns the new position."""
 
@@ -801,11 +911,53 @@ def _SkipGroup(buffer, pos, end):
       return pos
     pos = new_pos
 
+
+def _DecodeGroup(buffer, pos):
+  """Decode group.  Returns the UnknownFieldSet and new position."""
+
+  unknown_field_set = containers.UnknownFieldSet()
+  while 1:
+    (tag_bytes, pos) = ReadTag(buffer, pos)
+    (tag, _) = _DecodeVarint(tag_bytes, 0)
+    field_number, wire_type = wire_format.UnpackTag(tag)
+    if wire_type == wire_format.WIRETYPE_END_GROUP:
+      break
+    (data, pos) = _DecodeUnknownField(buffer, pos, wire_type)
+    # pylint: disable=protected-access
+    unknown_field_set._add(field_number, wire_type, data)
+
+  return (unknown_field_set, pos)
+
+
+def _DecodeUnknownField(buffer, pos, wire_type):
+  """Decode a unknown field.  Returns the UnknownField and new position."""
+
+  if wire_type == wire_format.WIRETYPE_VARINT:
+    (data, pos) = _DecodeVarint(buffer, pos)
+  elif wire_type == wire_format.WIRETYPE_FIXED64:
+    (data, pos) = _DecodeFixed64(buffer, pos)
+  elif wire_type == wire_format.WIRETYPE_FIXED32:
+    (data, pos) = _DecodeFixed32(buffer, pos)
+  elif wire_type == wire_format.WIRETYPE_LENGTH_DELIMITED:
+    (size, pos) = _DecodeVarint(buffer, pos)
+    data = buffer[pos:pos+size]
+    pos += size
+  elif wire_type == wire_format.WIRETYPE_START_GROUP:
+    (data, pos) = _DecodeGroup(buffer, pos)
+  elif wire_type == wire_format.WIRETYPE_END_GROUP:
+    return (0, -1)
+  else:
+    raise _DecodeError('Wrong wire type in tag.')
+
+  return (data, pos)
+
+
 def _EndGroup(buffer, pos, end):
   """Skipping an END_GROUP tag returns -1 to tell the parent loop to break."""
 
   return -1
 
+
 def _SkipFixed32(buffer, pos, end):
   """Skip a fixed32 value.  Returns the new position."""
 
@@ -814,6 +966,14 @@ def _SkipFixed32(buffer, pos, end):
     raise _DecodeError('Truncated message.')
   return pos
 
+
+def _DecodeFixed32(buffer, pos):
+  """Decode a fixed32."""
+
+  new_pos = pos + 4
+  return (struct.unpack('<I', buffer[pos:new_pos])[0], new_pos)
+
+
 def _RaiseInvalidWireType(buffer, pos, end):
   """Skip function for unknown wire types.  Raises an exception."""
 
diff --git a/python/google/protobuf/internal/descriptor_database_test.py b/python/google/protobuf/internal/descriptor_database_test.py
index f97477b3..97e5315a 100644
--- a/python/google/protobuf/internal/descriptor_database_test.py
+++ b/python/google/protobuf/internal/descriptor_database_test.py
@@ -43,6 +43,7 @@ import warnings
 from google.protobuf import unittest_pb2
 from google.protobuf import descriptor_pb2
 from google.protobuf.internal import factory_test2_pb2
+from google.protobuf.internal import no_package_pb2
 from google.protobuf import descriptor_database
 
 
@@ -52,7 +53,10 @@ class DescriptorDatabaseTest(unittest.TestCase):
     db = descriptor_database.DescriptorDatabase()
     file_desc_proto = descriptor_pb2.FileDescriptorProto.FromString(
         factory_test2_pb2.DESCRIPTOR.serialized_pb)
+    file_desc_proto2 = descriptor_pb2.FileDescriptorProto.FromString(
+        no_package_pb2.DESCRIPTOR.serialized_pb)
     db.Add(file_desc_proto)
+    db.Add(file_desc_proto2)
 
     self.assertEqual(file_desc_proto, db.FindFileByName(
         'google/protobuf/internal/factory_test2.proto'))
@@ -76,6 +80,10 @@ class DescriptorDatabaseTest(unittest.TestCase):
     # Can find enum value.
     self.assertEqual(file_desc_proto, db.FindFileContainingSymbol(
         'google.protobuf.python.internal.Factory2Enum.FACTORY_2_VALUE_0'))
+    self.assertEqual(file_desc_proto, db.FindFileContainingSymbol(
+        'google.protobuf.python.internal.FACTORY_2_VALUE_0'))
+    self.assertEqual(file_desc_proto2, db.FindFileContainingSymbol(
+        '.NO_PACKAGE_VALUE_0'))
     # Can find top level extension.
     self.assertEqual(file_desc_proto, db.FindFileContainingSymbol(
         'google.protobuf.python.internal.another_field'))
diff --git a/python/google/protobuf/internal/descriptor_pool_test.py b/python/google/protobuf/internal/descriptor_pool_test.py
index 2cbf7813..1b72b0b9 100644
--- a/python/google/protobuf/internal/descriptor_pool_test.py
+++ b/python/google/protobuf/internal/descriptor_pool_test.py
@@ -36,7 +36,6 @@ __author__ = 'matthewtoia@google.com (Matt Toia)'
 
 import copy
 import os
-import sys
 import warnings
 
 try:
@@ -55,6 +54,7 @@ from google.protobuf.internal import factory_test1_pb2
 from google.protobuf.internal import factory_test2_pb2
 from google.protobuf.internal import file_options_test_pb2
 from google.protobuf.internal import more_messages_pb2
+from google.protobuf.internal import no_package_pb2
 from google.protobuf import descriptor
 from google.protobuf import descriptor_database
 from google.protobuf import descriptor_pool
@@ -120,7 +120,6 @@ class DescriptorPoolTestBase(object):
     self.assertIsInstance(file_desc5, descriptor.FileDescriptor)
     self.assertEqual('google/protobuf/unittest.proto',
                      file_desc5.name)
-
     # Tests the generated pool.
     assert descriptor_pool.Default().FindFileContainingSymbol(
         'google.protobuf.python.internal.Factory2Message.one_more_field')
@@ -129,6 +128,32 @@ class DescriptorPoolTestBase(object):
     assert descriptor_pool.Default().FindFileContainingSymbol(
         'protobuf_unittest.TestService')
 
+    # Can find field.
+    file_desc6 = self.pool.FindFileContainingSymbol(
+        'google.protobuf.python.internal.Factory1Message.list_value')
+    self.assertIsInstance(file_desc6, descriptor.FileDescriptor)
+    self.assertEqual('google/protobuf/internal/factory_test1.proto',
+                     file_desc6.name)
+
+    # Can find top level Enum value.
+    file_desc7 = self.pool.FindFileContainingSymbol(
+        'google.protobuf.python.internal.FACTORY_1_VALUE_0')
+    self.assertIsInstance(file_desc7, descriptor.FileDescriptor)
+    self.assertEqual('google/protobuf/internal/factory_test1.proto',
+                     file_desc7.name)
+
+    # Can find nested Enum value.
+    file_desc8 = self.pool.FindFileContainingSymbol(
+        'protobuf_unittest.TestAllTypes.FOO')
+    self.assertIsInstance(file_desc8, descriptor.FileDescriptor)
+    self.assertEqual('google/protobuf/unittest.proto',
+                     file_desc8.name)
+
+    # TODO(jieluo): Add tests for no package when b/13860351 is fixed.
+
+    self.assertRaises(KeyError, self.pool.FindFileContainingSymbol,
+                      'google.protobuf.python.internal.Factory1Message.none_field')
+
   def testFindFileContainingSymbolFailure(self):
     with self.assertRaises(KeyError):
       self.pool.FindFileContainingSymbol('Does not exist')
@@ -217,11 +242,10 @@ class DescriptorPoolTestBase(object):
 
   def testFindTypeErrors(self):
     self.assertRaises(TypeError, self.pool.FindExtensionByNumber, '')
+    self.assertRaises(KeyError, self.pool.FindMethodByName, '')
 
     # TODO(jieluo): Fix python to raise correct errors.
     if api_implementation.Type() == 'cpp':
-      self.assertRaises(TypeError, self.pool.FindMethodByName, 0)
-      self.assertRaises(KeyError, self.pool.FindMethodByName, '')
       error_type = TypeError
     else:
       error_type = AttributeError
@@ -231,6 +255,7 @@ class DescriptorPoolTestBase(object):
     self.assertRaises(error_type, self.pool.FindEnumTypeByName, 0)
     self.assertRaises(error_type, self.pool.FindOneofByName, 0)
     self.assertRaises(error_type, self.pool.FindServiceByName, 0)
+    self.assertRaises(error_type, self.pool.FindMethodByName, 0)
     self.assertRaises(error_type, self.pool.FindFileContainingSymbol, 0)
     if api_implementation.Type() == 'python':
       error_type = KeyError
@@ -275,11 +300,6 @@ class DescriptorPoolTestBase(object):
       self.pool.FindEnumTypeByName('Does not exist')
 
   def testFindFieldByName(self):
-    if isinstance(self, SecondaryDescriptorFromDescriptorDB):
-      if api_implementation.Type() == 'cpp':
-        # TODO(jieluo): Fix cpp extension to find field correctly
-        # when descriptor pool is using an underlying database.
-        return
     field = self.pool.FindFieldByName(
         'google.protobuf.python.internal.Factory1Message.list_value')
     self.assertEqual(field.name, 'list_value')
@@ -290,11 +310,6 @@ class DescriptorPoolTestBase(object):
       self.pool.FindFieldByName('Does not exist')
 
   def testFindOneofByName(self):
-    if isinstance(self, SecondaryDescriptorFromDescriptorDB):
-      if api_implementation.Type() == 'cpp':
-        # TODO(jieluo): Fix cpp extension to find oneof correctly
-        # when descriptor pool is using an underlying database.
-        return
     oneof = self.pool.FindOneofByName(
         'google.protobuf.python.internal.Factory2Message.oneof_field')
     self.assertEqual(oneof.name, 'oneof_field')
@@ -302,11 +317,6 @@ class DescriptorPoolTestBase(object):
       self.pool.FindOneofByName('Does not exist')
 
   def testFindExtensionByName(self):
-    if isinstance(self, SecondaryDescriptorFromDescriptorDB):
-      if api_implementation.Type() == 'cpp':
-        # TODO(jieluo): Fix cpp extension to find extension correctly
-        # when descriptor pool is using an underlying database.
-        return
     # An extension defined in a message.
     extension = self.pool.FindExtensionByName(
         'google.protobuf.python.internal.Factory2Message.one_more_field')
@@ -382,6 +392,11 @@ class DescriptorPoolTestBase(object):
     with self.assertRaises(KeyError):
       self.pool.FindServiceByName('Does not exist')
 
+    method = self.pool.FindMethodByName('protobuf_unittest.TestService.Foo')
+    self.assertIs(method.containing_service, service)
+    with self.assertRaises(KeyError):
+      self.pool.FindMethodByName('protobuf_unittest.TestService.Doesnotexist')
+
   def testUserDefinedDB(self):
     db = descriptor_database.DescriptorDatabase()
     self.pool = descriptor_pool.DescriptorPool(db)
@@ -601,6 +616,8 @@ class CreateDescriptorPoolTest(DescriptorPoolTestBase, unittest.TestCase):
         unittest_import_pb2.DESCRIPTOR.serialized_pb))
     self.pool.Add(descriptor_pb2.FileDescriptorProto.FromString(
         unittest_pb2.DESCRIPTOR.serialized_pb))
+    self.pool.Add(descriptor_pb2.FileDescriptorProto.FromString(
+        no_package_pb2.DESCRIPTOR.serialized_pb))
 
 
 class SecondaryDescriptorFromDescriptorDB(DescriptorPoolTestBase,
@@ -620,6 +637,8 @@ class SecondaryDescriptorFromDescriptorDB(DescriptorPoolTestBase,
         unittest_import_pb2.DESCRIPTOR.serialized_pb))
     db.Add(descriptor_pb2.FileDescriptorProto.FromString(
         unittest_pb2.DESCRIPTOR.serialized_pb))
+    db.Add(descriptor_pb2.FileDescriptorProto.FromString(
+        no_package_pb2.DESCRIPTOR.serialized_pb))
     self.pool = descriptor_pool.DescriptorPool(descriptor_db=db)
 
 
@@ -746,11 +765,7 @@ class MessageField(object):
     test.assertEqual(msg_desc, field_desc.containing_type)
     test.assertEqual(field_type_desc, field_desc.message_type)
     test.assertEqual(file_desc, field_desc.file)
-    # TODO(jieluo): Fix python and cpp extension diff for message field
-    # default value.
-    if api_implementation.Type() == 'cpp':
-      test.assertRaises(
-          NotImplementedError, getattr, field_desc, 'default_value')
+    test.assertEqual(field_desc.default_value, None)
 
 
 class StringField(object):
diff --git a/python/google/protobuf/internal/descriptor_test.py b/python/google/protobuf/internal/descriptor_test.py
index 02a43d15..af6bece1 100755
--- a/python/google/protobuf/internal/descriptor_test.py
+++ b/python/google/protobuf/internal/descriptor_test.py
@@ -452,6 +452,17 @@ class DescriptorTest(unittest.TestCase):
     self.assertEqual('attribute is not writable: has_options',
                      str(e.exception))
 
+  def testDefault(self):
+    message_descriptor = unittest_pb2.TestAllTypes.DESCRIPTOR
+    field = message_descriptor.fields_by_name['repeated_int32']
+    self.assertEqual(field.default_value, [])
+    field = message_descriptor.fields_by_name['repeated_nested_message']
+    self.assertEqual(field.default_value, [])
+    field = message_descriptor.fields_by_name['optionalgroup']
+    self.assertEqual(field.default_value, None)
+    field = message_descriptor.fields_by_name['optional_nested_message']
+    self.assertEqual(field.default_value, None)
+
 
 class NewDescriptorTest(DescriptorTest):
   """Redo the same tests as above, but with a separate DescriptorPool."""
diff --git a/python/google/protobuf/internal/factory_test1.proto b/python/google/protobuf/internal/factory_test1.proto
index d2fbbeec..f5bd0383 100644
--- a/python/google/protobuf/internal/factory_test1.proto
+++ b/python/google/protobuf/internal/factory_test1.proto
@@ -56,3 +56,17 @@ message Factory1Message {
 
   extensions 1000 to max;
 }
+
+message Factory1MethodRequest {
+  optional string argument = 1;
+}
+
+message Factory1MethodResponse {
+  optional string result = 1;
+}
+
+service Factory1Service {
+  // Dummy method for this dummy service.
+  rpc Factory1Method(Factory1MethodRequest) returns (Factory1MethodResponse) {
+  }
+}
diff --git a/python/google/protobuf/internal/message_factory_test.py b/python/google/protobuf/internal/message_factory_test.py
index 6df52ed2..b97e3f65 100644
--- a/python/google/protobuf/internal/message_factory_test.py
+++ b/python/google/protobuf/internal/message_factory_test.py
@@ -142,10 +142,8 @@ class MessageFactoryTest(unittest.TestCase):
       self.assertEqual('test2', msg1.Extensions[ext2])
       self.assertEqual(None,
                        msg1.Extensions._FindExtensionByNumber(12321))
+      self.assertRaises(TypeError, len, msg1.Extensions)
       if api_implementation.Type() == 'cpp':
-        # TODO(jieluo): Fix len to return the correct value.
-        # self.assertEqual(2, len(msg1.Extensions))
-        self.assertEqual(len(msg1.Extensions), len(msg1.Extensions))
         self.assertRaises(TypeError,
                           msg1.Extensions._FindExtensionByName, 0)
         self.assertRaises(TypeError,
diff --git a/python/google/protobuf/internal/message_test.py b/python/google/protobuf/internal/message_test.py
index 61a56a67..1a865398 100755
--- a/python/google/protobuf/internal/message_test.py
+++ b/python/google/protobuf/internal/message_test.py
@@ -1,4 +1,5 @@
 #! /usr/bin/env python
+# -*- coding: utf-8 -*-
 #
 # Protocol Buffers - Google's data interchange format
 # Copyright 2008 Google Inc.  All rights reserved.
@@ -49,6 +50,7 @@ import copy
 import math
 import operator
 import pickle
+import pydoc
 import six
 import sys
 import warnings
@@ -72,6 +74,7 @@ from google.protobuf import message_factory
 from google.protobuf import text_format
 from google.protobuf.internal import api_implementation
 from google.protobuf.internal import encoder
+from google.protobuf.internal import more_extensions_pb2
 from google.protobuf.internal import packed_field_test_pb2
 from google.protobuf.internal import test_util
 from google.protobuf.internal import testing_refleaks
@@ -415,6 +418,37 @@ class MessageTest(BaseTestCase):
     empty.ParseFromString(populated.SerializeToString())
     self.assertEqual(str(empty), '')
 
+  def testMergeFromRepeatedField(self, message_module):
+    msg = message_module.TestAllTypes()
+    msg.repeated_int32.append(1)
+    msg.repeated_int32.append(3)
+    msg.repeated_nested_message.add(bb=1)
+    msg.repeated_nested_message.add(bb=2)
+    other_msg = message_module.TestAllTypes()
+    other_msg.repeated_nested_message.add(bb=3)
+    other_msg.repeated_nested_message.add(bb=4)
+    other_msg.repeated_int32.append(5)
+    other_msg.repeated_int32.append(7)
+
+    msg.repeated_int32.MergeFrom(other_msg.repeated_int32)
+    self.assertEqual(4, len(msg.repeated_int32))
+
+    msg.repeated_nested_message.MergeFrom(other_msg.repeated_nested_message)
+    self.assertEqual([1, 2, 3, 4],
+                     [m.bb for m in msg.repeated_nested_message])
+
+  def testAddWrongRepeatedNestedField(self, message_module):
+    msg = message_module.TestAllTypes()
+    try:
+      msg.repeated_nested_message.add('wrong')
+    except TypeError:
+      pass
+    try:
+      msg.repeated_nested_message.add(value_field='wrong')
+    except ValueError:
+      pass
+    self.assertEqual(len(msg.repeated_nested_message), 0)
+
   def testRepeatedNestedFieldIteration(self, message_module):
     msg = message_module.TestAllTypes()
     msg.repeated_nested_message.add(bb=1)
@@ -645,6 +679,82 @@ class MessageTest(BaseTestCase):
     m.payload.repeated_int32.extend([])
     self.assertTrue(m.HasField('payload'))
 
+  def testMergeFrom(self, message_module):
+    m1 = message_module.TestAllTypes()
+    m2 = message_module.TestAllTypes()
+    # Cpp extension will lazily create a sub message which is immutable.
+    self.assertEqual(0, m1.optional_nested_message.bb)
+    m2.optional_nested_message.bb = 1
+    # Make sure cmessage pointing to a mutable message after merge instead of
+    # the lazily created message.
+    m1.MergeFrom(m2)
+    self.assertEqual(1, m1.optional_nested_message.bb)
+
+    # Test more nested sub message.
+    msg1 = message_module.NestedTestAllTypes()
+    msg2 = message_module.NestedTestAllTypes()
+    self.assertEqual(0, msg1.child.payload.optional_nested_message.bb)
+    msg2.child.payload.optional_nested_message.bb = 1
+    msg1.MergeFrom(msg2)
+    self.assertEqual(1, msg1.child.payload.optional_nested_message.bb)
+
+    # Test repeated field.
+    self.assertEqual(msg1.payload.repeated_nested_message,
+                     msg1.payload.repeated_nested_message)
+    msg2.payload.repeated_nested_message.add().bb = 1
+    msg1.MergeFrom(msg2)
+    self.assertEqual(1, len(msg1.payload.repeated_nested_message))
+    self.assertEqual(1, msg1.payload.repeated_nested_message[0].bb)
+
+  def testMergeFromString(self, message_module):
+    m1 = message_module.TestAllTypes()
+    m2 = message_module.TestAllTypes()
+    # Cpp extension will lazily create a sub message which is immutable.
+    self.assertEqual(0, m1.optional_nested_message.bb)
+    m2.optional_nested_message.bb = 1
+    # Make sure cmessage pointing to a mutable message after merge instead of
+    # the lazily created message.
+    m1.MergeFromString(m2.SerializeToString())
+    self.assertEqual(1, m1.optional_nested_message.bb)
+
+  @unittest.skipIf(six.PY2, 'memoryview objects are not supported on py2')
+  def testMergeFromStringUsingMemoryViewWorksInPy3(self, message_module):
+    m2 = message_module.TestAllTypes()
+    m2.optional_string = 'scalar string'
+    m2.repeated_string.append('repeated string')
+    m2.optional_bytes = b'scalar bytes'
+    m2.repeated_bytes.append(b'repeated bytes')
+
+    serialized = m2.SerializeToString()
+    memview = memoryview(serialized)
+    m1 = message_module.TestAllTypes.FromString(memview)
+
+    self.assertEqual(m1.optional_bytes, b'scalar bytes')
+    self.assertEqual(m1.repeated_bytes, [b'repeated bytes'])
+    self.assertEqual(m1.optional_string, 'scalar string')
+    self.assertEqual(m1.repeated_string, ['repeated string'])
+    # Make sure that the memoryview was correctly converted to bytes, and
+    # that a sub-sliced memoryview is not being used.
+    self.assertIsInstance(m1.optional_bytes, bytes)
+    self.assertIsInstance(m1.repeated_bytes[0], bytes)
+    self.assertIsInstance(m1.optional_string, six.text_type)
+    self.assertIsInstance(m1.repeated_string[0], six.text_type)
+
+  @unittest.skipIf(six.PY3, 'memoryview is supported by py3')
+  def testMergeFromStringUsingMemoryViewIsPy2Error(self, message_module):
+    memview = memoryview(b'')
+    with self.assertRaises(TypeError):
+      message_module.TestAllTypes.FromString(memview)
+
+  def testMergeFromEmpty(self, message_module):
+    m1 = message_module.TestAllTypes()
+    # Cpp extension will lazily create a sub message which is immutable.
+    self.assertEqual(0, m1.optional_nested_message.bb)
+    self.assertFalse(m1.HasField('optional_nested_message'))
+    # Make sure the sub message is still immutable after merge from empty.
+    m1.MergeFromString(b'')  # field state should not change
+    self.assertFalse(m1.HasField('optional_nested_message'))
+
   def ensureNestedMessageExists(self, msg, attribute):
     """Make sure that a nested message object exists.
 
@@ -1067,14 +1177,8 @@ class MessageTest(BaseTestCase):
     with self.assertRaises(AttributeError):
       m.repeated_int32 = []
     m.repeated_int32.append(1)
-    if api_implementation.Type() == 'cpp':
-      # For test coverage: cpp has a different path if composite
-      # field is in cache
-      with self.assertRaises(TypeError):
-        m.repeated_int32 = []
-    else:
-      with self.assertRaises(AttributeError):
-        m.repeated_int32 = []
+    with self.assertRaises(AttributeError):
+      m.repeated_int32 = []
 
 
 # Class to test proto2-only features (required, extensions, etc.)
@@ -1169,6 +1273,21 @@ class Proto2Test(BaseTestCase):
     msg = unittest_pb2.TestAllTypes()
     self.assertRaises(AttributeError, getattr, msg, 'Extensions')
 
+  def testMergeFromExtensions(self):
+    msg1 = more_extensions_pb2.TopLevelMessage()
+    msg2 = more_extensions_pb2.TopLevelMessage()
+    # Cpp extension will lazily create a sub message which is immutable.
+    self.assertEqual(0, msg1.submessage.Extensions[
+        more_extensions_pb2.optional_int_extension])
+    self.assertFalse(msg1.HasField('submessage'))
+    msg2.submessage.Extensions[
+        more_extensions_pb2.optional_int_extension] = 123
+    # Make sure cmessage and extensions pointing to a mutable message
+    # after merge instead of the lazily created message.
+    msg1.MergeFrom(msg2)
+    self.assertEqual(123, msg1.submessage.Extensions[
+        more_extensions_pb2.optional_int_extension])
+
   def testGoldenExtensions(self):
     golden_data = test_util.GoldenFileData('golden_message')
     golden_message = unittest_pb2.TestAllExtensions()
@@ -1316,6 +1435,15 @@ class Proto2Test(BaseTestCase):
       unittest_pb2.TestAllTypes(repeated_nested_enum='FOO')
 
 
+  def test_documentation(self):
+    # Also used by the interactive help() function.
+    doc = pydoc.html.document(unittest_pb2.TestAllTypes, 'message')
+    self.assertIn('class TestAllTypes', doc)
+    self.assertIn('SerializePartialToString', doc)
+    self.assertIn('repeated_float', doc)
+    base = unittest_pb2.TestAllTypes.__bases__[0]
+    self.assertRaises(AttributeError, getattr, base, '_extensions_by_name')
+
 
 # Class to test proto3-only features/behavior (updated field presence & enums)
 class Proto3Test(BaseTestCase):
@@ -1539,10 +1667,8 @@ class Proto3Test(BaseTestCase):
     self.assertEqual(True, msg2.map_bool_bool[True])
     self.assertEqual(2, msg2.map_int32_enum[888])
     self.assertEqual(456, msg2.map_int32_enum[123])
-    # TODO(jieluo): Add cpp extension support.
-    if api_implementation.Type() == 'python':
-      self.assertEqual('{-123: -456}',
-                       str(msg2.map_int32_int32))
+    self.assertEqual('{-123: -456}',
+                     str(msg2.map_int32_int32))
 
   def testMapEntryAlwaysSerialized(self):
     msg = map_unittest_pb2.TestMap()
@@ -1603,11 +1729,10 @@ class Proto3Test(BaseTestCase):
     self.assertIn(123, msg2.map_int32_foreign_message)
     self.assertIn(-456, msg2.map_int32_foreign_message)
     self.assertEqual(2, len(msg2.map_int32_foreign_message))
+    msg2.map_int32_foreign_message[123].c = 1
     # TODO(jieluo): Fix text format for message map.
-    # TODO(jieluo): Add cpp extension support.
-    if api_implementation.Type() == 'python':
-      self.assertEqual(15,
-                       len(str(msg2.map_int32_foreign_message)))
+    self.assertIn(str(msg2.map_int32_foreign_message),
+                  ('{-456: , 123: c: 1\n}', '{123: c: 1\n, -456: }'))
 
   def testNestedMessageMapItemDelete(self):
     msg = map_unittest_pb2.TestMap()
@@ -1721,6 +1846,15 @@ class Proto3Test(BaseTestCase):
     self.assertEqual(10, msg2.map_int32_foreign_message[222].c)
     self.assertFalse(msg2.map_int32_foreign_message[222].HasField('d'))
 
+    # Test when cpp extension cache a map.
+    m1 = map_unittest_pb2.TestMap()
+    m2 = map_unittest_pb2.TestMap()
+    self.assertEqual(m1.map_int32_foreign_message,
+                     m1.map_int32_foreign_message)
+    m2.map_int32_foreign_message[123].c = 10
+    m1.MergeFrom(m2)
+    self.assertEqual(10, m2.map_int32_foreign_message[123].c)
+
   def testMergeFromBadType(self):
     msg = map_unittest_pb2.TestMap()
     with self.assertRaisesRegexp(
@@ -1972,7 +2106,7 @@ class Proto3Test(BaseTestCase):
   def testMapValidAfterFieldCleared(self):
     # Map needs to work even if field is cleared.
     # For the C++ implementation this tests the correctness of
-    # ScalarMapContainer::Release()
+    # MapContainer::Release()
     msg = map_unittest_pb2.TestMap()
     int32_map = msg.map_int32_int32
 
@@ -1988,7 +2122,7 @@ class Proto3Test(BaseTestCase):
   def testMessageMapValidAfterFieldCleared(self):
     # Map needs to work even if field is cleared.
     # For the C++ implementation this tests the correctness of
-    # ScalarMapContainer::Release()
+    # MapContainer::Release()
     msg = map_unittest_pb2.TestMap()
     int32_foreign_message = msg.map_int32_foreign_message
 
@@ -1998,6 +2132,24 @@ class Proto3Test(BaseTestCase):
     self.assertEqual(b'', msg.SerializeToString())
     self.assertTrue(2 in int32_foreign_message.keys())
 
+  def testMessageMapItemValidAfterTopMessageCleared(self):
+    # Message map item needs to work even if it is cleared.
+    # For the C++ implementation this tests the correctness of
+    # MapContainer::Release()
+    msg = map_unittest_pb2.TestMap()
+    msg.map_int32_all_types[2].optional_string = 'bar'
+
+    if api_implementation.Type() == 'cpp':
+      # Need to keep the map reference because of b/27942626.
+      # TODO(jieluo): Remove it.
+      unused_map = msg.map_int32_all_types  # pylint: disable=unused-variable
+    msg_value = msg.map_int32_all_types[2]
+    msg.Clear()
+
+    # Reset to trigger sync between repeated field and map in c++.
+    msg.map_int32_all_types[3].optional_string = 'foo'
+    self.assertEqual(msg_value.optional_string, 'bar')
+
   def testMapIterInvalidatedByClearField(self):
     # Map iterator is invalidated when field is cleared.
     # But this case does need to not crash the interpreter.
@@ -2058,6 +2210,80 @@ class Proto3Test(BaseTestCase):
     msg.map_string_foreign_message['foo'].c = 5
     self.assertEqual(0, len(msg.FindInitializationErrors()))
 
+  def testStrictUtf8Check(self):
+    # Test u'\ud801' is rejected at parser in both python2 and python3.
+    serialized = (b'r\x03\xed\xa0\x81')
+    msg = unittest_proto3_arena_pb2.TestAllTypes()
+    with self.assertRaises(Exception) as context:
+      msg.MergeFromString(serialized)
+    if api_implementation.Type() == 'python':
+      self.assertIn('optional_string', str(context.exception))
+    else:
+      self.assertIn('Error parsing message', str(context.exception))
+
+    # Test optional_string=u'😍' is accepted.
+    serialized = unittest_proto3_arena_pb2.TestAllTypes(
+        optional_string=u'😍').SerializeToString()
+    msg2 = unittest_proto3_arena_pb2.TestAllTypes()
+    msg2.MergeFromString(serialized)
+    self.assertEqual(msg2.optional_string, u'😍')
+
+    msg = unittest_proto3_arena_pb2.TestAllTypes(
+        optional_string=u'\ud001')
+    self.assertEqual(msg.optional_string, u'\ud001')
+
+  @unittest.skipIf(six.PY2, 'Surrogates are acceptable in python2')
+  def testSurrogatesInPython3(self):
+    # Surrogates like U+D83D is an invalid unicode character, it is
+    # supported by Python2 only because in some builds, unicode strings
+    # use 2-bytes code units. Since Python 3.3, we don't have this problem.
+    #
+    # Surrogates are utf16 code units, in a unicode string they are invalid
+    # characters even when they appear in pairs like u'\ud801\udc01'. Protobuf
+    # Python3 reject such cases at setters and parsers. Python2 accpect it
+    # to keep same features with the language itself. 'Unpaired pairs'
+    # like u'\ud801' are rejected at parsers when strict utf8 check is enabled
+    # in proto3 to keep same behavior with c extension.
+
+    # Surrogates are rejected at setters in Python3.
+    with self.assertRaises(ValueError):
+      unittest_proto3_arena_pb2.TestAllTypes(
+          optional_string=u'\ud801\udc01')
+    with self.assertRaises(ValueError):
+      unittest_proto3_arena_pb2.TestAllTypes(
+          optional_string=b'\xed\xa0\x81')
+    with self.assertRaises(ValueError):
+      unittest_proto3_arena_pb2.TestAllTypes(
+          optional_string=u'\ud801')
+    with self.assertRaises(ValueError):
+      unittest_proto3_arena_pb2.TestAllTypes(
+          optional_string=u'\ud801\ud801')
+
+  @unittest.skipIf(six.PY3, 'Surrogates are rejected at setters in Python3')
+  def testSurrogatesInPython2(self):
+    # Test optional_string=u'\ud801\udc01'.
+    # surrogate pair is acceptable in python2.
+    msg = unittest_proto3_arena_pb2.TestAllTypes(
+        optional_string=u'\ud801\udc01')
+    # TODO(jieluo): Change pure python to have same behavior with c extension.
+    # Some build in python2 consider u'\ud801\udc01' and u'\U00010401' are
+    # equal, some are not equal.
+    if api_implementation.Type() == 'python':
+      self.assertEqual(msg.optional_string, u'\ud801\udc01')
+    else:
+      self.assertEqual(msg.optional_string, u'\U00010401')
+    serialized = msg.SerializeToString()
+    msg2 = unittest_proto3_arena_pb2.TestAllTypes()
+    msg2.MergeFromString(serialized)
+    self.assertEqual(msg2.optional_string, u'\U00010401')
+
+    # Python2 does not reject surrogates at setters.
+    msg = unittest_proto3_arena_pb2.TestAllTypes(
+        optional_string=b'\xed\xa0\x81')
+    unittest_proto3_arena_pb2.TestAllTypes(
+        optional_string=u'\ud801')
+    unittest_proto3_arena_pb2.TestAllTypes(
+        optional_string=u'\ud801\ud801')
 
 
 class ValidTypeNamesTest(BaseTestCase):
diff --git a/python/google/protobuf/internal/no_package.proto b/python/google/protobuf/internal/no_package.proto
index 3546dcc3..49eda959 100644
--- a/python/google/protobuf/internal/no_package.proto
+++ b/python/google/protobuf/internal/no_package.proto
@@ -1,3 +1,33 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
 syntax = "proto2";
 
 enum NoPackageEnum {
diff --git a/python/google/protobuf/internal/python_message.py b/python/google/protobuf/internal/python_message.py
index 975e3b4d..ab5d160f 100755
--- a/python/google/protobuf/internal/python_message.py
+++ b/python/google/protobuf/internal/python_message.py
@@ -56,6 +56,7 @@ import sys
 import weakref
 
 import six
+from six.moves import range
 
 # We use "as" to avoid name collisions with variables.
 from google.protobuf.internal import api_implementation
@@ -124,6 +125,21 @@ class GeneratedProtocolMessageType(type):
       Newly-allocated class.
     """
     descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
+
+    # If a concrete class already exists for this descriptor, don't try to
+    # create another.  Doing so will break any messages that already exist with
+    # the existing class.
+    #
+    # The C++ implementation appears to have its own internal `PyMessageFactory`
+    # to achieve similar results.
+    #
+    # This most commonly happens in `text_format.py` when using descriptors from
+    # a custom pool; it calls symbol_database.Global().getPrototype() on a
+    # descriptor which already has an existing concrete class.
+    new_class = getattr(descriptor, '_concrete_class', None)
+    if new_class:
+      return new_class
+
     if descriptor.full_name in well_known_types.WKTBASES:
       bases += (well_known_types.WKTBASES[descriptor.full_name],)
     _AddClassAttributesForNestedExtensions(descriptor, dictionary)
@@ -151,6 +167,16 @@ class GeneratedProtocolMessageType(type):
         type.
     """
     descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
+
+    # If this is an _existing_ class looked up via `_concrete_class` in the
+    # __new__ method above, then we don't need to re-initialize anything.
+    existing_class = getattr(descriptor, '_concrete_class', None)
+    if existing_class:
+      assert existing_class is cls, (
+          'Duplicate `GeneratedProtocolMessageType` created for descriptor %r'
+          % (descriptor.full_name))
+      return
+
     cls._decoders_by_tag = {}
     if (descriptor.has_options and
         descriptor.GetOptions().message_set_wire_format):
@@ -245,6 +271,7 @@ def _AddSlots(message_descriptor, dictionary):
                              '_cached_byte_size_dirty',
                              '_fields',
                              '_unknown_fields',
+                             '_unknown_field_set',
                              '_is_present_in_parent',
                              '_listener',
                              '_listener_for_children',
@@ -271,6 +298,13 @@ def _IsMessageMapField(field):
   return value_type.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE
 
 
+def _IsStrictUtf8Check(field):
+  if field.containing_type.syntax != 'proto3':
+    return False
+  enforce_utf8 = True
+  return enforce_utf8
+
+
 def _AttachFieldHelpers(cls, field_descriptor):
   is_repeated = (field_descriptor.label == _FieldDescriptor.LABEL_REPEATED)
   is_packable = (is_repeated and
@@ -322,10 +356,16 @@ def _AttachFieldHelpers(cls, field_descriptor):
       field_decoder = decoder.MapDecoder(
           field_descriptor, _GetInitializeDefaultForMap(field_descriptor),
           is_message_map)
+    elif decode_type == _FieldDescriptor.TYPE_STRING:
+      is_strict_utf8_check = _IsStrictUtf8Check(field_descriptor)
+      field_decoder = decoder.StringDecoder(
+          field_descriptor.number, is_repeated, is_packed,
+          field_descriptor, field_descriptor._default_constructor,
+          is_strict_utf8_check)
     else:
       field_decoder = type_checkers.TYPE_TO_DECODER[decode_type](
-              field_descriptor.number, is_repeated, is_packed,
-              field_descriptor, field_descriptor._default_constructor)
+          field_descriptor.number, is_repeated, is_packed,
+          field_descriptor, field_descriptor._default_constructor)
 
     cls._decoders_by_tag[tag_bytes] = (field_decoder, oneof_descriptor)
 
@@ -422,6 +462,9 @@ def _DefaultValueConstructorForField(field):
     # _concrete_class may not yet be initialized.
     message_type = field.message_type
     def MakeSubMessageDefault(message):
+      assert getattr(message_type, '_concrete_class', None), (
+          'Uninitialized concrete class found for field %r (message type %r)'
+          % (field.full_name, message_type.full_name))
       result = message_type._concrete_class()
       result._SetListener(
           _OneofListener(message, field)
@@ -477,6 +520,9 @@ def _AddInitMethod(message_descriptor, cls):
     # _unknown_fields is () when empty for efficiency, and will be turned into
     # a list if fields are added.
     self._unknown_fields = ()
+    # _unknown_field_set is None when empty for efficiency, and will be
+    # turned into UnknownFieldSet struct if fields are added.
+    self._unknown_field_set = None      # pylint: disable=protected-access
     self._is_present_in_parent = False
     self._listener = message_listener_mod.NullMessageListener()
     self._listener_for_children = _Listener(self)
@@ -584,6 +630,14 @@ def _AddPropertiesForField(field, cls):
     _AddPropertiesForNonRepeatedScalarField(field, cls)
 
 
+class _FieldProperty(property):
+  __slots__ = ('DESCRIPTOR',)
+
+  def __init__(self, descriptor, getter, setter, doc):
+    property.__init__(self, getter, setter, doc=doc)
+    self.DESCRIPTOR = descriptor
+
+
 def _AddPropertiesForRepeatedField(field, cls):
   """Adds a public property for a "repeated" protocol message field.  Clients
   can use this property to get the value of the field, which will be either a
@@ -625,7 +679,7 @@ def _AddPropertiesForRepeatedField(field, cls):
                          '"%s" in protocol message object.' % proto_field_name)
 
   doc = 'Magic attribute generated for "%s" proto field.' % proto_field_name
-  setattr(cls, property_name, property(getter, setter, doc=doc))
+  setattr(cls, property_name, _FieldProperty(field, getter, setter, doc=doc))
 
 
 def _AddPropertiesForNonRepeatedScalarField(field, cls):
@@ -681,7 +735,7 @@ def _AddPropertiesForNonRepeatedScalarField(field, cls):
 
   # Add a property to encapsulate the getter/setter.
   doc = 'Magic attribute generated for "%s" proto field.' % proto_field_name
-  setattr(cls, property_name, property(getter, setter, doc=doc))
+  setattr(cls, property_name, _FieldProperty(field, getter, setter, doc=doc))
 
 
 def _AddPropertiesForNonRepeatedCompositeField(field, cls):
@@ -725,7 +779,7 @@ def _AddPropertiesForNonRepeatedCompositeField(field, cls):
 
   # Add a property to encapsulate the getter.
   doc = 'Magic attribute generated for "%s" proto field.' % proto_field_name
-  setattr(cls, property_name, property(getter, setter, doc=doc))
+  setattr(cls, property_name, _FieldProperty(field, getter, setter, doc=doc))
 
 
 def _AddPropertiesForExtensions(descriptor, cls):
@@ -949,13 +1003,8 @@ def _AddEqualsMethod(message_descriptor, cls):
     if not self.ListFields() == other.ListFields():
       return False
 
-    # Sort unknown fields because their order shouldn't affect equality test.
-    unknown_fields = list(self._unknown_fields)
-    unknown_fields.sort()
-    other_unknown_fields = list(other._unknown_fields)
-    other_unknown_fields.sort()
-
-    return unknown_fields == other_unknown_fields
+    # pylint: disable=protected-access
+    return self._unknown_field_set == other._unknown_field_set
 
   cls.__eq__ = __eq__
 
@@ -1078,6 +1127,13 @@ def _AddSerializePartialToStringMethod(message_descriptor, cls):
 def _AddMergeFromStringMethod(message_descriptor, cls):
   """Helper for _AddMessageMethods()."""
   def MergeFromString(self, serialized):
+    if isinstance(serialized, memoryview) and six.PY2:
+      raise TypeError(
+          'memoryview not supported in Python 2 with the pure Python proto '
+          'implementation: this is to maintain compatibility with the C++ '
+          'implementation')
+
+    serialized = memoryview(serialized)
     length = len(serialized)
     try:
       if self._InternalParse(serialized, 0, length) != length:
@@ -1095,26 +1151,54 @@ def _AddMergeFromStringMethod(message_descriptor, cls):
   local_ReadTag = decoder.ReadTag
   local_SkipField = decoder.SkipField
   decoders_by_tag = cls._decoders_by_tag
-  is_proto3 = message_descriptor.syntax == "proto3"
 
   def InternalParse(self, buffer, pos, end):
+    """Create a message from serialized bytes.
+
+    Args:
+      self: Message, instance of the proto message object.
+      buffer: memoryview of the serialized data.
+      pos: int, position to start in the serialized data.
+      end: int, end position of the serialized data.
+
+    Returns:
+      Message object.
+    """
+    # Guard against internal misuse, since this function is called internally
+    # quite extensively, and its easy to accidentally pass bytes.
+    assert isinstance(buffer, memoryview)
     self._Modified()
     field_dict = self._fields
-    unknown_field_list = self._unknown_fields
+    # pylint: disable=protected-access
+    unknown_field_set = self._unknown_field_set
     while pos != end:
       (tag_bytes, new_pos) = local_ReadTag(buffer, pos)
       field_decoder, field_desc = decoders_by_tag.get(tag_bytes, (None, None))
       if field_decoder is None:
-        value_start_pos = new_pos
-        new_pos = local_SkipField(buffer, new_pos, end, tag_bytes)
+        if not self._unknown_fields:   # pylint: disable=protected-access
+          self._unknown_fields = []    # pylint: disable=protected-access
+        if unknown_field_set is None:
+          # pylint: disable=protected-access
+          self._unknown_field_set = containers.UnknownFieldSet()
+          # pylint: disable=protected-access
+          unknown_field_set = self._unknown_field_set
+        # pylint: disable=protected-access
+        (tag, _) = decoder._DecodeVarint(tag_bytes, 0)
+        field_number, wire_type = wire_format.UnpackTag(tag)
+        # TODO(jieluo): remove old_pos.
+        old_pos = new_pos
+        (data, new_pos) = decoder._DecodeUnknownField(
+            buffer, new_pos, wire_type)  # pylint: disable=protected-access
         if new_pos == -1:
           return pos
-        if (not is_proto3 or
-            api_implementation.GetPythonProto3PreserveUnknownsDefault()):
-          if not unknown_field_list:
-            unknown_field_list = self._unknown_fields = []
-          unknown_field_list.append(
-              (tag_bytes, buffer[value_start_pos:new_pos]))
+        # pylint: disable=protected-access
+        unknown_field_set._add(field_number, wire_type, data)
+        # TODO(jieluo): remove _unknown_fields.
+        new_pos = local_SkipField(buffer, old_pos, end, tag_bytes)
+        if new_pos == -1:
+          return pos
+        self._unknown_fields.append(
+            (tag_bytes, buffer[old_pos:new_pos].tobytes()))
         pos = new_pos
       else:
         pos = field_decoder(buffer, new_pos, end, self, field_dict)
@@ -1259,6 +1343,10 @@ def _AddMergeFromMethod(cls):
       if not self._unknown_fields:
         self._unknown_fields = []
       self._unknown_fields.extend(msg._unknown_fields)
+      # pylint: disable=protected-access
+      if self._unknown_field_set is None:
+        self._unknown_field_set = containers.UnknownFieldSet()
+      self._unknown_field_set._extend(msg._unknown_field_set)
 
   cls.MergeFrom = MergeFrom
 
@@ -1291,12 +1379,25 @@ def _Clear(self):
   # Clear fields.
   self._fields = {}
   self._unknown_fields = ()
+  # pylint: disable=protected-access
+  if self._unknown_field_set is not None:
+    self._unknown_field_set._clear()
+    self._unknown_field_set = None
+
   self._oneofs = {}
   self._Modified()
 
 
+def _UnknownFields(self):
+  if self._unknown_field_set is None:  # pylint: disable=protected-access
+    # pylint: disable=protected-access
+    self._unknown_field_set = containers.UnknownFieldSet()
+  return self._unknown_field_set    # pylint: disable=protected-access
+
+
 def _DiscardUnknownFields(self):
   self._unknown_fields = []
+  self._unknown_field_set = None      # pylint: disable=protected-access
   for field, value in self.ListFields():
     if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
       if field.label == _FieldDescriptor.LABEL_REPEATED:
@@ -1335,6 +1436,7 @@ def _AddMessageMethods(message_descriptor, cls):
   _AddReduceMethod(cls)
   # Adds methods which do not depend on cls.
   cls.Clear = _Clear
+  cls.UnknownFields = _UnknownFields
   cls.DiscardUnknownFields = _DiscardUnknownFields
   cls._SetListener = _SetListener
 
@@ -1471,6 +1573,10 @@ class _ExtensionDict(object):
     if extension_handle.label == _FieldDescriptor.LABEL_REPEATED:
       result = extension_handle._default_constructor(self._extended_message)
     elif extension_handle.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+      assert getattr(extension_handle.message_type, '_concrete_class', None), (
+          'Uninitialized concrete class found for field %r (message type %r)'
+          % (extension_handle.full_name,
+             extension_handle.message_type.full_name))
       result = extension_handle.message_type._concrete_class()
       try:
         result._SetListener(self._extended_message._listener_for_children)
diff --git a/python/google/protobuf/internal/reflection_test.py b/python/google/protobuf/internal/reflection_test.py
index 0306ff46..31ceda24 100755
--- a/python/google/protobuf/internal/reflection_test.py
+++ b/python/google/protobuf/internal/reflection_test.py
@@ -64,6 +64,10 @@ from google.protobuf.internal import testing_refleaks
 from google.protobuf.internal import decoder
 
 
+if six.PY3:
+  long = int  # pylint: disable=redefined-builtin,invalid-name
+
+
 BaseTestCase = testing_refleaks.BaseTestCase
 
 
@@ -647,10 +651,7 @@ class ReflectionTest(BaseTestCase):
     TestGetAndDeserialize('optional_int32', 1, int)
     TestGetAndDeserialize('optional_int32', 1 << 30, int)
     TestGetAndDeserialize('optional_uint32', 1 << 30, int)
-    try:
-      integer_64 = long
-    except NameError:  # Python3
-      integer_64 = int
+    integer_64 = long
     if struct.calcsize('L') == 4:
       # Python only has signed ints, so 32-bit python can't fit an uint32
       # in an int.
@@ -1103,6 +1104,7 @@ class ReflectionTest(BaseTestCase):
     self.assertEqual(23, myproto_instance.foo_field)
     self.assertTrue(myproto_instance.HasField('foo_field'))
 
+  @testing_refleaks.SkipReferenceLeakChecker('MakeDescriptor is not repeatable')
   def testDescriptorProtoSupport(self):
     # Hand written descriptors/reflection are only supported by the pure-Python
     # implementation of the API.
@@ -1141,7 +1143,8 @@ class ReflectionTest(BaseTestCase):
     self.assertTrue('price' in desc.fields_by_name)
     self.assertTrue('owners' in desc.fields_by_name)
 
-    class CarMessage(six.with_metaclass(reflection.GeneratedProtocolMessageType, message.Message)):
+    class CarMessage(six.with_metaclass(reflection.GeneratedProtocolMessageType,
+                                        message.Message)):
       DESCRIPTOR = desc
 
     prius = CarMessage()
@@ -2435,7 +2438,7 @@ class SerializationTest(BaseTestCase):
 
     first_proto = unittest_pb2.TestAllTypes()
     test_util.SetAllFields(first_proto)
-    serialized = first_proto.SerializeToString()
+    serialized = memoryview(first_proto.SerializeToString())
 
     for truncation_point in range(len(serialized) + 1):
       try:
@@ -2857,6 +2860,38 @@ class SerializationTest(BaseTestCase):
     self.assertEqual(unittest_pb2.REPEATED_NESTED_ENUM_EXTENSION_FIELD_NUMBER,
       51)
 
+  def testFieldProperties(self):
+    cls = unittest_pb2.TestAllTypes
+    self.assertIs(cls.optional_int32.DESCRIPTOR,
+                  cls.DESCRIPTOR.fields_by_name['optional_int32'])
+    self.assertEqual(cls.OPTIONAL_INT32_FIELD_NUMBER,
+                     cls.optional_int32.DESCRIPTOR.number)
+    self.assertIs(cls.optional_nested_message.DESCRIPTOR,
+                  cls.DESCRIPTOR.fields_by_name['optional_nested_message'])
+    self.assertEqual(cls.OPTIONAL_NESTED_MESSAGE_FIELD_NUMBER,
+                     cls.optional_nested_message.DESCRIPTOR.number)
+    self.assertIs(cls.repeated_int32.DESCRIPTOR,
+                  cls.DESCRIPTOR.fields_by_name['repeated_int32'])
+    self.assertEqual(cls.REPEATED_INT32_FIELD_NUMBER,
+                     cls.repeated_int32.DESCRIPTOR.number)
+
+  def testFieldDataDescriptor(self):
+    msg = unittest_pb2.TestAllTypes()
+    msg.optional_int32 = 42
+    self.assertEqual(unittest_pb2.TestAllTypes.optional_int32.__get__(msg), 42)
+    unittest_pb2.TestAllTypes.optional_int32.__set__(msg, 25)
+    self.assertEqual(msg.optional_int32, 25)
+    with self.assertRaises(AttributeError):
+      del msg.optional_int32
+    try:
+      unittest_pb2.ForeignMessage.c.__get__(msg)
+    except TypeError:
+      pass  # The cpp implementation cannot mix fields from other messages.
+            # This test exercises a specific check that avoids a crash.
+    else:
+      pass  # The python implementation allows fields from other messages.
+            # This is useless, but works.
+
   def testInitKwargs(self):
     proto = unittest_pb2.TestAllTypes(
         optional_int32=1,
@@ -2963,6 +2998,7 @@ class ClassAPITest(BaseTestCase):
   @unittest.skipIf(
       api_implementation.Type() == 'cpp' and api_implementation.Version() == 2,
       'C++ implementation requires a call to MakeDescriptor()')
+  @testing_refleaks.SkipReferenceLeakChecker('MakeClass is not repeatable')
   def testMakeClassWithNestedDescriptor(self):
     leaf_desc = descriptor.Descriptor('leaf', 'package.parent.child.leaf', '',
                                       containing_type=None, fields=[],
@@ -2980,10 +3016,7 @@ class ClassAPITest(BaseTestCase):
                                         containing_type=None, fields=[],
                                         nested_types=[child_desc, sibling_desc],
                                         enum_types=[], extensions=[])
-    message_class = reflection.MakeClass(parent_desc)
-    self.assertIn('child', message_class.__dict__)
-    self.assertIn('sibling', message_class.__dict__)
-    self.assertIn('leaf', message_class.child.__dict__)
+    reflection.MakeClass(parent_desc)
 
   def _GetSerializedFileDescriptor(self, name):
     """Get a serialized representation of a test FileDescriptorProto.
diff --git a/python/google/protobuf/internal/text_format_test.py b/python/google/protobuf/internal/text_format_test.py
index 237a2d50..c68f42d2 100755
--- a/python/google/protobuf/internal/text_format_test.py
+++ b/python/google/protobuf/internal/text_format_test.py
@@ -33,20 +33,19 @@
 
 """Test for google.protobuf.text_format."""
 
-__author__ = 'kenton@google.com (Kenton Varda)'
-
-
+import io
 import math
 import re
-import six
 import string
+import textwrap
 
+import six
+
+# pylint: disable=g-import-not-at-top
 try:
-  import unittest2 as unittest  # PY26, pylint: disable=g-import-not-at-top
+  import unittest2 as unittest  # PY26
 except ImportError:
-  import unittest  # pylint: disable=g-import-not-at-top
-
-from google.protobuf.internal import _parameterized
+  import unittest
 
 from google.protobuf import any_pb2
 from google.protobuf import any_test_pb2
@@ -54,12 +53,13 @@ from google.protobuf import map_unittest_pb2
 from google.protobuf import unittest_mset_pb2
 from google.protobuf import unittest_pb2
 from google.protobuf import unittest_proto3_arena_pb2
-from google.protobuf.internal import api_implementation
 from google.protobuf.internal import any_test_pb2 as test_extend_any
 from google.protobuf.internal import message_set_extensions_pb2
 from google.protobuf.internal import test_util
 from google.protobuf import descriptor_pool
 from google.protobuf import text_format
+from google.protobuf.internal import _parameterized
+# pylint: enable=g-import-not-at-top
 
 
 # Low-level nuts-n-bolts tests.
@@ -100,8 +100,8 @@ class TextFormatBase(unittest.TestCase):
     return text
 
 
-@_parameterized.parameters((unittest_pb2), (unittest_proto3_arena_pb2))
-class TextFormatTest(TextFormatBase):
+@_parameterized.parameters(unittest_pb2, unittest_proto3_arena_pb2)
+class TextFormatMessageToStringTests(TextFormatBase):
 
   def testPrintExotic(self, message_module):
     message = message_module.TestAllTypes()
@@ -154,6 +154,40 @@ class TextFormatTest(TextFormatBase):
         'repeated_int32: 1 repeated_int32: 1 repeated_int32: 3 '
         'repeated_string: "Google" repeated_string: "Zurich"')
 
+  def VerifyPrintShortFormatRepeatedFields(self, message_module, as_one_line):
+    message = message_module.TestAllTypes()
+    message.repeated_int32.append(1)
+    message.repeated_string.append('Google')
+    message.repeated_string.append('Hello,World')
+    message.repeated_foreign_enum.append(unittest_pb2.FOREIGN_FOO)
+    message.repeated_foreign_enum.append(unittest_pb2.FOREIGN_BAR)
+    message.repeated_foreign_enum.append(unittest_pb2.FOREIGN_BAZ)
+    message.optional_nested_message.bb = 3
+    for i in (21, 32):
+      msg = message.repeated_nested_message.add()
+      msg.bb = i
+    expected_ascii = (
+        'optional_nested_message {\n  bb: 3\n}\n'
+        'repeated_int32: [1]\n'
+        'repeated_string: "Google"\n'
+        'repeated_string: "Hello,World"\n'
+        'repeated_nested_message {\n  bb: 21\n}\n'
+        'repeated_nested_message {\n  bb: 32\n}\n'
+        'repeated_foreign_enum: [FOREIGN_FOO, FOREIGN_BAR, FOREIGN_BAZ]\n')
+    if as_one_line:
+      expected_ascii = expected_ascii.replace('\n ', '').replace('\n', '')
+    actual_ascii = text_format.MessageToString(
+        message, use_short_repeated_primitives=True,
+        as_one_line=as_one_line)
+    self.CompareToGoldenText(actual_ascii, expected_ascii)
+    parsed_message = message_module.TestAllTypes()
+    text_format.Parse(actual_ascii, parsed_message)
+    self.assertEqual(parsed_message, message)
+
+  def tesPrintShortFormatRepeatedFields(self, message_module, as_one_line):
+    self.VerifyPrintShortFormatRepeatedFields(message_module, False)
+    self.VerifyPrintShortFormatRepeatedFields(message_module, True)
+
   def testPrintNestedNewLineInStringAsOneLine(self, message_module):
     message = message_module.TestAllTypes()
     message.optional_string = 'a\nnew\nline'
@@ -213,13 +247,18 @@ class TextFormatTest(TextFormatBase):
 
   def testPrintRawUtf8String(self, message_module):
     message = message_module.TestAllTypes()
-    message.repeated_string.append(u'\u00fc\ua71f')
+    message.repeated_string.append(u'\u00fc\t\ua71f')
     text = text_format.MessageToString(message, as_utf8=True)
-    self.CompareToGoldenText(text, 'repeated_string: "\303\274\352\234\237"\n')
+    golden_unicode = u'repeated_string: "\u00fc\\t\ua71f"\n'
+    golden_text = golden_unicode if six.PY3 else golden_unicode.encode('utf-8')
+    # MessageToString always returns a native str.
+    self.CompareToGoldenText(text, golden_text)
     parsed_message = message_module.TestAllTypes()
     text_format.Parse(text, parsed_message)
-    self.assertEqual(message, parsed_message,
-                     '\n%s != %s' % (message, parsed_message))
+    self.assertEqual(
+        message, parsed_message, '\n%s != %s  (%s != %s)' %
+        (message, parsed_message, message.repeated_string[0],
+         parsed_message.repeated_string[0]))
 
   def testPrintFloatFormat(self, message_module):
     # Check that float_format argument is passed to sub-message formatting.
@@ -259,6 +298,36 @@ class TextFormatTest(TextFormatBase):
     message.c = 123
     self.assertEqual('c: 123\n', str(message))
 
+  def testMessageToStringUnicode(self, message_module):
+    golden_unicode = u'Á short desçription and a 🍌.'
+    golden_bytes = golden_unicode.encode('utf-8')
+    message = message_module.TestAllTypes()
+    message.optional_string = golden_unicode
+    message.optional_bytes = golden_bytes
+    text = text_format.MessageToString(message, as_utf8=True)
+    golden_message = textwrap.dedent(
+        'optional_string: "Á short desçription and a 🍌."\n'
+        'optional_bytes: '
+        r'"\303\201 short des\303\247ription and a \360\237\215\214."'
+        '\n')
+    self.CompareToGoldenText(text, golden_message)
+
+  def testMessageToStringASCII(self, message_module):
+    golden_unicode = u'Á short desçription and a 🍌.'
+    golden_bytes = golden_unicode.encode('utf-8')
+    message = message_module.TestAllTypes()
+    message.optional_string = golden_unicode
+    message.optional_bytes = golden_bytes
+    text = text_format.MessageToString(message, as_utf8=False)  # ASCII
+    golden_message = (
+        'optional_string: '
+        r'"\303\201 short des\303\247ription and a \360\237\215\214."'
+        '\n'
+        'optional_bytes: '
+        r'"\303\201 short des\303\247ription and a \360\237\215\214."'
+        '\n')
+    self.CompareToGoldenText(text, golden_message)
+
   def testPrintField(self, message_module):
     message = message_module.TestAllTypes()
     field = message.DESCRIPTOR.fields_by_name['optional_float']
@@ -289,6 +358,45 @@ class TextFormatTest(TextFormatBase):
     self.assertEqual('0.0', out.getvalue())
     out.close()
 
+
+@_parameterized.parameters(unittest_pb2, unittest_proto3_arena_pb2)
+class TextFormatMessageToTextBytesTests(TextFormatBase):
+
+  def testMessageToBytes(self, message_module):
+    message = message_module.ForeignMessage()
+    message.c = 123
+    self.assertEqual(b'c: 123\n', text_format.MessageToBytes(message))
+
+  def testRawUtf8RoundTrip(self, message_module):
+    message = message_module.TestAllTypes()
+    message.repeated_string.append(u'\u00fc\t\ua71f')
+    utf8_text = text_format.MessageToBytes(message, as_utf8=True)
+    golden_bytes = b'repeated_string: "\xc3\xbc\\t\xea\x9c\x9f"\n'
+    self.CompareToGoldenText(utf8_text, golden_bytes)
+    parsed_message = message_module.TestAllTypes()
+    text_format.Parse(utf8_text, parsed_message)
+    self.assertEqual(
+        message, parsed_message, '\n%s != %s  (%s != %s)' %
+        (message, parsed_message, message.repeated_string[0],
+         parsed_message.repeated_string[0]))
+
+  def testEscapedUtf8ASCIIRoundTrip(self, message_module):
+    message = message_module.TestAllTypes()
+    message.repeated_string.append(u'\u00fc\t\ua71f')
+    ascii_text = text_format.MessageToBytes(message)  # as_utf8=False default
+    golden_bytes = b'repeated_string: "\\303\\274\\t\\352\\234\\237"\n'
+    self.CompareToGoldenText(ascii_text, golden_bytes)
+    parsed_message = message_module.TestAllTypes()
+    text_format.Parse(ascii_text, parsed_message)
+    self.assertEqual(
+        message, parsed_message, '\n%s != %s  (%s != %s)' %
+        (message, parsed_message, message.repeated_string[0],
+         parsed_message.repeated_string[0]))
+
+
+@_parameterized.parameters(unittest_pb2, unittest_proto3_arena_pb2)
+class TextFormatParserTests(TextFormatBase):
+
   def testParseAllFields(self, message_module):
     message = message_module.TestAllTypes()
     test_util.SetAllFields(message)
@@ -318,14 +426,14 @@ class TextFormatTest(TextFormatBase):
     if message_module is unittest_pb2:
       test_util.ExpectAllFieldsSet(self, message)
 
-    if six.PY2:
-      msg2 = message_module.TestAllTypes()
-      text = (u'optional_string: "café"')
-      text_format.Merge(text, msg2)
-      self.assertEqual(msg2.optional_string, u'café')
-      msg2.Clear()
-      text_format.Parse(text, msg2)
-      self.assertEqual(msg2.optional_string, u'café')
+    msg2 = message_module.TestAllTypes()
+    text = (u'optional_string: "café"')
+    text_format.Merge(text, msg2)
+    self.assertEqual(msg2.optional_string, u'café')
+    msg2.Clear()
+    self.assertEqual(msg2.optional_string, u'')
+    text_format.Parse(text, msg2)
+    self.assertEqual(msg2.optional_string, u'café')
 
   def testParseExotic(self, message_module):
     message = message_module.TestAllTypes()
@@ -425,7 +533,8 @@ class TextFormatTest(TextFormatBase):
     message = message_module.TestAllTypes()
     text = 'optional_nested_enum: BARR'
     six.assertRaisesRegex(self, text_format.ParseError,
-                          (r'1:23 : Enum type "\w+.TestAllTypes.NestedEnum" '
+                          (r'1:23 : \'optional_nested_enum: BARR\': '
+                           r'Enum type "\w+.TestAllTypes.NestedEnum" '
                            r'has no value named BARR.'), text_format.Parse,
                           text, message)
 
@@ -433,7 +542,8 @@ class TextFormatTest(TextFormatBase):
     message = message_module.TestAllTypes()
     text = 'optional_int32: bork'
     six.assertRaisesRegex(self, text_format.ParseError,
-                          ('1:17 : Couldn\'t parse integer: bork'),
+                          ('1:17 : \'optional_int32: bork\': '
+                           'Couldn\'t parse integer: bork'),
                           text_format.Parse, text, message)
 
   def testParseStringFieldUnescape(self, message_module):
@@ -457,6 +567,96 @@ class TextFormatTest(TextFormatBase):
                      message.repeated_string[4])
     self.assertEqual(SLASH + 'x20', message.repeated_string[5])
 
+  def testParseOneof(self, message_module):
+    m = message_module.TestAllTypes()
+    m.oneof_uint32 = 11
+    m2 = message_module.TestAllTypes()
+    text_format.Parse(text_format.MessageToString(m), m2)
+    self.assertEqual('oneof_uint32', m2.WhichOneof('oneof_field'))
+
+  def testParseMultipleOneof(self, message_module):
+    m_string = '\n'.join(['oneof_uint32: 11', 'oneof_string: "foo"'])
+    m2 = message_module.TestAllTypes()
+    with six.assertRaisesRegex(self, text_format.ParseError,
+                               ' is specified along with field '):
+      text_format.Parse(m_string, m2)
+
+  # This example contains non-ASCII codepoint unicode data as literals
+  # which should come through as utf-8 for bytes, and as the unicode
+  # itself for string fields.  It also demonstrates escaped binary data.
+  # The ur"" string prefix is unfortunately missing from Python 3
+  # so we resort to double escaping our \s so that they come through.
+  _UNICODE_SAMPLE = u"""
+      optional_bytes: 'Á short desçription'
+      optional_string: 'Á short desçription'
+      repeated_bytes: '\\303\\201 short des\\303\\247ription'
+      repeated_bytes: '\\x12\\x34\\x56\\x78\\x90\\xab\\xcd\\xef'
+      repeated_string: '\\xd0\\x9f\\xd1\\x80\\xd0\\xb8\\xd0\\xb2\\xd0\\xb5\\xd1\\x82'
+      """
+  _BYTES_SAMPLE = _UNICODE_SAMPLE.encode('utf-8')
+  _GOLDEN_UNICODE = u'Á short desçription'
+  _GOLDEN_BYTES = _GOLDEN_UNICODE.encode('utf-8')
+  _GOLDEN_BYTES_1 = b'\x12\x34\x56\x78\x90\xab\xcd\xef'
+  _GOLDEN_STR_0 = u'Привет'
+
+  def testParseUnicode(self, message_module):
+    m = message_module.TestAllTypes()
+    text_format.Parse(self._UNICODE_SAMPLE, m)
+    self.assertEqual(m.optional_bytes, self._GOLDEN_BYTES)
+    self.assertEqual(m.optional_string, self._GOLDEN_UNICODE)
+    self.assertEqual(m.repeated_bytes[0], self._GOLDEN_BYTES)
+    # repeated_bytes[1] contained simple \ escaped non-UTF-8 raw binary data.
+    self.assertEqual(m.repeated_bytes[1], self._GOLDEN_BYTES_1)
+    # repeated_string[0] contained \ escaped data representing the UTF-8
+    # representation of _GOLDEN_STR_0 - it needs to decode as such.
+    self.assertEqual(m.repeated_string[0], self._GOLDEN_STR_0)
+
+  def testParseBytes(self, message_module):
+    m = message_module.TestAllTypes()
+    text_format.Parse(self._BYTES_SAMPLE, m)
+    self.assertEqual(m.optional_bytes, self._GOLDEN_BYTES)
+    self.assertEqual(m.optional_string, self._GOLDEN_UNICODE)
+    self.assertEqual(m.repeated_bytes[0], self._GOLDEN_BYTES)
+    # repeated_bytes[1] contained simple \ escaped non-UTF-8 raw binary data.
+    self.assertEqual(m.repeated_bytes[1], self._GOLDEN_BYTES_1)
+    # repeated_string[0] contained \ escaped data representing the UTF-8
+    # representation of _GOLDEN_STR_0 - it needs to decode as such.
+    self.assertEqual(m.repeated_string[0], self._GOLDEN_STR_0)
+
+  def testFromBytesFile(self, message_module):
+    m = message_module.TestAllTypes()
+    f = io.BytesIO(self._BYTES_SAMPLE)
+    text_format.ParseLines(f, m)
+    self.assertEqual(m.optional_bytes, self._GOLDEN_BYTES)
+    self.assertEqual(m.optional_string, self._GOLDEN_UNICODE)
+    self.assertEqual(m.repeated_bytes[0], self._GOLDEN_BYTES)
+
+  def testFromUnicodeFile(self, message_module):
+    m = message_module.TestAllTypes()
+    f = io.StringIO(self._UNICODE_SAMPLE)
+    text_format.ParseLines(f, m)
+    self.assertEqual(m.optional_bytes, self._GOLDEN_BYTES)
+    self.assertEqual(m.optional_string, self._GOLDEN_UNICODE)
+    self.assertEqual(m.repeated_bytes[0], self._GOLDEN_BYTES)
+
+  def testFromBytesLines(self, message_module):
+    m = message_module.TestAllTypes()
+    text_format.ParseLines(self._BYTES_SAMPLE.split(b'\n'), m)
+    self.assertEqual(m.optional_bytes, self._GOLDEN_BYTES)
+    self.assertEqual(m.optional_string, self._GOLDEN_UNICODE)
+    self.assertEqual(m.repeated_bytes[0], self._GOLDEN_BYTES)
+
+  def testFromUnicodeLines(self, message_module):
+    m = message_module.TestAllTypes()
+    text_format.ParseLines(self._UNICODE_SAMPLE.split(u'\n'), m)
+    self.assertEqual(m.optional_bytes, self._GOLDEN_BYTES)
+    self.assertEqual(m.optional_string, self._GOLDEN_UNICODE)
+    self.assertEqual(m.repeated_bytes[0], self._GOLDEN_BYTES)
+
+
+@_parameterized.parameters(unittest_pb2, unittest_proto3_arena_pb2)
+class TextFormatMergeTests(TextFormatBase):
+
   def testMergeDuplicateScalars(self, message_module):
     message = message_module.TestAllTypes()
     text = ('optional_int32: 42 ' 'optional_int32: 67')
@@ -472,26 +672,12 @@ class TextFormatTest(TextFormatBase):
     self.assertTrue(r is message)
     self.assertEqual(2, message.optional_nested_message.bb)
 
-  def testParseOneof(self, message_module):
-    m = message_module.TestAllTypes()
-    m.oneof_uint32 = 11
-    m2 = message_module.TestAllTypes()
-    text_format.Parse(text_format.MessageToString(m), m2)
-    self.assertEqual('oneof_uint32', m2.WhichOneof('oneof_field'))
-
   def testMergeMultipleOneof(self, message_module):
     m_string = '\n'.join(['oneof_uint32: 11', 'oneof_string: "foo"'])
     m2 = message_module.TestAllTypes()
     text_format.Merge(m_string, m2)
     self.assertEqual('oneof_string', m2.WhichOneof('oneof_field'))
 
-  def testParseMultipleOneof(self, message_module):
-    m_string = '\n'.join(['oneof_uint32: 11', 'oneof_string: "foo"'])
-    m2 = message_module.TestAllTypes()
-    with self.assertRaisesRegexp(text_format.ParseError,
-                                 ' is specified along with field '):
-      text_format.Parse(m_string, m2)
-
 
 # These are tests that aren't fundamentally specific to proto2, but are at
 # the moment because of differences between the proto2 and proto3 test schemas.
@@ -938,7 +1124,7 @@ class Proto2Tests(TextFormatBase):
                  '}\n')
     six.assertRaisesRegex(self,
                           text_format.ParseError,
-                          '5:1 : Expected ">".',
+                          '5:1 : \'}\': Expected ">".',
                           text_format.Parse,
                           malformed,
                           message,
@@ -981,7 +1167,8 @@ class Proto2Tests(TextFormatBase):
     with self.assertRaises(text_format.ParseError) as e:
       text_format.Parse(text, message)
     self.assertEqual(str(e.exception),
-                     '1:27 : Expected identifier or number, got "bb".')
+                     '1:27 : \'optional_nested_message { "bb": 1 }\': '
+                     'Expected identifier or number, got "bb".')
 
   def testParseBadExtension(self):
     message = unittest_pb2.TestAllExtensions()
@@ -998,7 +1185,8 @@ class Proto2Tests(TextFormatBase):
     message = unittest_pb2.TestAllTypes()
     text = 'optional_nested_enum: 100'
     six.assertRaisesRegex(self, text_format.ParseError,
-                          (r'1:23 : Enum type "\w+.TestAllTypes.NestedEnum" '
+                          (r'1:23 : \'optional_nested_enum: 100\': '
+                           r'Enum type "\w+.TestAllTypes.NestedEnum" '
                            r'has no value with number 100.'), text_format.Parse,
                           text, message)
 
@@ -1448,6 +1636,26 @@ class TokenizerTest(unittest.TestCase):
     self.assertEqual(0, text_format._ConsumeUint64(tokenizer))
     self.assertTrue(tokenizer.AtEnd())
 
+  def testConsumeOctalIntegers(self):
+    """Test support for C style octal integers."""
+    text = '00 -00 04 0755 -010 007 -0033 08 -09 01'
+    tokenizer = text_format.Tokenizer(text.splitlines())
+    self.assertEqual(0, tokenizer.ConsumeInteger())
+    self.assertEqual(0, tokenizer.ConsumeInteger())
+    self.assertEqual(4, tokenizer.ConsumeInteger())
+    self.assertEqual(0o755, tokenizer.ConsumeInteger())
+    self.assertEqual(-0o10, tokenizer.ConsumeInteger())
+    self.assertEqual(7, tokenizer.ConsumeInteger())
+    self.assertEqual(-0o033, tokenizer.ConsumeInteger())
+    with self.assertRaises(text_format.ParseError):
+      tokenizer.ConsumeInteger()  # 08
+    tokenizer.NextToken()
+    with self.assertRaises(text_format.ParseError):
+      tokenizer.ConsumeInteger()  # -09
+    tokenizer.NextToken()
+    self.assertEqual(1, tokenizer.ConsumeInteger())
+    self.assertTrue(tokenizer.AtEnd())
+
   def testConsumeByteString(self):
     text = '"string1\''
     tokenizer = text_format.Tokenizer(text.splitlines())
@@ -1556,6 +1764,12 @@ class TokenizerTest(unittest.TestCase):
                      tokenizer.ConsumeCommentOrTrailingComment())
     self.assertTrue(tokenizer.AtEnd())
 
+  def testHugeString(self):
+    # With pathologic backtracking, fails with Forge OOM.
+    text = '"' + 'a' * (10 * 1024 * 1024) + '"'
+    tokenizer = text_format.Tokenizer(text.splitlines(), skip_comments=False)
+    tokenizer.ConsumeString()
+
 
 # Tests for pretty printer functionality.
 @_parameterized.parameters((unittest_pb2), (unittest_proto3_arena_pb2))
diff --git a/python/google/protobuf/internal/type_checkers.py b/python/google/protobuf/internal/type_checkers.py
index 4a76cd4e..0807e7f7 100755
--- a/python/google/protobuf/internal/type_checkers.py
+++ b/python/google/protobuf/internal/type_checkers.py
@@ -185,6 +185,14 @@ class UnicodeValueChecker(object):
                          'encoding. Non-UTF-8 strings must be converted to '
                          'unicode objects before being added.' %
                          (proposed_value))
+    else:
+      try:
+        proposed_value.encode('utf8')
+      except UnicodeEncodeError:
+        raise ValueError('%.1024r isn\'t a valid unicode string and '
+                         'can\'t be encoded in UTF-8.'%
+                         (proposed_value))
+
     return proposed_value
 
   def DefaultValue(self):
diff --git a/python/google/protobuf/internal/unknown_fields_test.py b/python/google/protobuf/internal/unknown_fields_test.py
index 8b7de2e7..fceadf71 100755
--- a/python/google/protobuf/internal/unknown_fields_test.py
+++ b/python/google/protobuf/internal/unknown_fields_test.py
@@ -49,20 +49,12 @@ from google.protobuf.internal import missing_enum_values_pb2
 from google.protobuf.internal import test_util
 from google.protobuf.internal import testing_refleaks
 from google.protobuf.internal import type_checkers
+from google.protobuf import descriptor
 
 
 BaseTestCase = testing_refleaks.BaseTestCase
 
 
-# CheckUnknownField() cannot be used by the C++ implementation because
-# some protect members are called. It is not a behavior difference
-# for python and C++ implementation.
-def SkipCheckUnknownFieldIfCppImplementation(func):
-  return unittest.skipIf(
-      api_implementation.Type() == 'cpp' and api_implementation.Version() == 2,
-      'Addtional test for pure python involved protect members')(func)
-
-
 class UnknownFieldsTest(BaseTestCase):
 
   def setUp(self):
@@ -80,23 +72,11 @@ class UnknownFieldsTest(BaseTestCase):
     # stdout.
     self.assertTrue(data == self.all_fields_data)
 
-  def expectSerializeProto3(self, preserve):
+  def testSerializeProto3(self):
+    # Verify proto3 unknown fields behavior.
     message = unittest_proto3_arena_pb2.TestEmptyMessage()
     message.ParseFromString(self.all_fields_data)
-    if preserve:
-      self.assertEqual(self.all_fields_data, message.SerializeToString())
-    else:
-      self.assertEqual(0, len(message.SerializeToString()))
-
-  def testSerializeProto3(self):
-    # Verify that proto3 unknown fields behavior.
-    default_preserve = (api_implementation
-                        .GetPythonProto3PreserveUnknownsDefault())
-    self.expectSerializeProto3(default_preserve)
-    api_implementation.SetPythonProto3PreserveUnknownsDefault(
-        not default_preserve)
-    self.expectSerializeProto3(not default_preserve)
-    api_implementation.SetPythonProto3PreserveUnknownsDefault(default_preserve)
+    self.assertEqual(self.all_fields_data, message.SerializeToString())
 
   def testByteSize(self):
     self.assertEqual(self.all_fields.ByteSize(), self.empty_message.ByteSize())
@@ -169,13 +149,15 @@ class UnknownFieldsAccessorsTest(BaseTestCase):
     self.empty_message = unittest_pb2.TestEmptyMessage()
     self.empty_message.ParseFromString(self.all_fields_data)
 
-  # CheckUnknownField() is an additional Pure Python check which checks
+  # InternalCheckUnknownField() is an additional Pure Python check which checks
   # a detail of unknown fields. It cannot be used by the C++
   # implementation because some protect members are called.
   # The test is added for historical reasons. It is not necessary as
   # serialized string is checked.
-
-  def CheckUnknownField(self, name, expected_value):
+  # TODO(jieluo): Remove message._unknown_fields.
+  def InternalCheckUnknownField(self, name, expected_value):
+    if api_implementation.Type() == 'cpp':
+      return
     field_descriptor = self.descriptor.fields_by_name[name]
     wire_type = type_checkers.FIELD_TYPE_TO_WIRE_TYPE[field_descriptor.type]
     field_tag = encoder.TagBytes(field_descriptor.number, wire_type)
@@ -183,36 +165,80 @@ class UnknownFieldsAccessorsTest(BaseTestCase):
     for tag_bytes, value in self.empty_message._unknown_fields:
       if tag_bytes == field_tag:
         decoder = unittest_pb2.TestAllTypes._decoders_by_tag[tag_bytes][0]
-        decoder(value, 0, len(value), self.all_fields, result_dict)
+        decoder(memoryview(value), 0, len(value), self.all_fields, result_dict)
     self.assertEqual(expected_value, result_dict[field_descriptor])
 
-  @SkipCheckUnknownFieldIfCppImplementation
+  def CheckUnknownField(self, name, unknown_fields, expected_value):
+    field_descriptor = self.descriptor.fields_by_name[name]
+    expected_type = type_checkers.FIELD_TYPE_TO_WIRE_TYPE[
+        field_descriptor.type]
+    for unknown_field in unknown_fields:
+      if unknown_field.field_number == field_descriptor.number:
+        self.assertEqual(expected_type, unknown_field.wire_type)
+        if expected_type == 3:
+          # Check group
+          self.assertEqual(expected_value[0],
+                           unknown_field.data[0].field_number)
+          self.assertEqual(expected_value[1], unknown_field.data[0].wire_type)
+          self.assertEqual(expected_value[2], unknown_field.data[0].data)
+          continue
+        if field_descriptor.label == descriptor.FieldDescriptor.LABEL_REPEATED:
+          self.assertIn(unknown_field.data, expected_value)
+        else:
+          self.assertEqual(expected_value, unknown_field.data)
+
   def testCheckUnknownFieldValue(self):
+    unknown_fields = self.empty_message.UnknownFields()
     # Test enum.
     self.CheckUnknownField('optional_nested_enum',
+                           unknown_fields,
                            self.all_fields.optional_nested_enum)
+    self.InternalCheckUnknownField('optional_nested_enum',
+                                   self.all_fields.optional_nested_enum)
+
     # Test repeated enum.
     self.CheckUnknownField('repeated_nested_enum',
+                           unknown_fields,
                            self.all_fields.repeated_nested_enum)
+    self.InternalCheckUnknownField('repeated_nested_enum',
+                                   self.all_fields.repeated_nested_enum)
 
     # Test varint.
     self.CheckUnknownField('optional_int32',
+                           unknown_fields,
                            self.all_fields.optional_int32)
+    self.InternalCheckUnknownField('optional_int32',
+                                   self.all_fields.optional_int32)
+
     # Test fixed32.
     self.CheckUnknownField('optional_fixed32',
+                           unknown_fields,
                            self.all_fields.optional_fixed32)
+    self.InternalCheckUnknownField('optional_fixed32',
+                                   self.all_fields.optional_fixed32)
 
     # Test fixed64.
     self.CheckUnknownField('optional_fixed64',
+                           unknown_fields,
                            self.all_fields.optional_fixed64)
+    self.InternalCheckUnknownField('optional_fixed64',
+                                   self.all_fields.optional_fixed64)
 
     # Test lengthd elimited.
     self.CheckUnknownField('optional_string',
-                           self.all_fields.optional_string)
+                           unknown_fields,
+                           self.all_fields.optional_string.encode('utf-8'))
+    self.InternalCheckUnknownField('optional_string',
+                                   self.all_fields.optional_string)
 
     # Test group.
     self.CheckUnknownField('optionalgroup',
-                           self.all_fields.optionalgroup)
+                           unknown_fields,
+                           (17, 0, 117))
+    self.InternalCheckUnknownField('optionalgroup',
+                                   self.all_fields.optionalgroup)
+
+    self.assertEqual(97, len(unknown_fields))
 
   def testCopyFrom(self):
     message = unittest_pb2.TestEmptyMessage()
@@ -230,9 +256,18 @@ class UnknownFieldsAccessorsTest(BaseTestCase):
     message.optional_int64 = 3
     message.optional_uint32 = 4
     destination = unittest_pb2.TestEmptyMessage()
+    unknown_fields = destination.UnknownFields()
+    self.assertEqual(0, len(unknown_fields))
     destination.ParseFromString(message.SerializeToString())
-
+    # ParseFromString clears the message thus unknown fields is invalid.
+    with self.assertRaises(ValueError) as context:
+      len(unknown_fields)
+    self.assertIn('UnknownFields does not exist.',
+                  str(context.exception))
+    unknown_fields = destination.UnknownFields()
+    self.assertEqual(2, len(unknown_fields))
     destination.MergeFrom(source)
+    self.assertEqual(4, len(unknown_fields))
     # Check that the fields where correctly merged, even stored in the unknown
     # fields set.
     message.ParseFromString(destination.SerializeToString())
@@ -241,9 +276,58 @@ class UnknownFieldsAccessorsTest(BaseTestCase):
     self.assertEqual(message.optional_int64, 3)
 
   def testClear(self):
+    unknown_fields = self.empty_message.UnknownFields()
     self.empty_message.Clear()
     # All cleared, even unknown fields.
     self.assertEqual(self.empty_message.SerializeToString(), b'')
+    with self.assertRaises(ValueError) as context:
+      len(unknown_fields)
+    self.assertIn('UnknownFields does not exist.',
+                  str(context.exception))
+
+  def testSubUnknownFields(self):
+    message = unittest_pb2.TestAllTypes()
+    message.optionalgroup.a = 123
+    destination = unittest_pb2.TestEmptyMessage()
+    destination.ParseFromString(message.SerializeToString())
+    sub_unknown_fields = destination.UnknownFields()[0].data
+    self.assertEqual(1, len(sub_unknown_fields))
+    self.assertEqual(sub_unknown_fields[0].data, 123)
+    destination.Clear()
+    with self.assertRaises(ValueError) as context:
+      len(sub_unknown_fields)
+    self.assertIn('UnknownFields does not exist.',
+                  str(context.exception))
+    with self.assertRaises(ValueError) as context:
+      # pylint: disable=pointless-statement
+      sub_unknown_fields[0]
+    self.assertIn('UnknownFields does not exist.',
+                  str(context.exception))
+    message.Clear()
+    message.optional_uint32 = 456
+    nested_message = unittest_pb2.NestedTestAllTypes()
+    nested_message.payload.optional_nested_message.ParseFromString(
+        message.SerializeToString())
+    unknown_fields = (
+        nested_message.payload.optional_nested_message.UnknownFields())
+    self.assertEqual(unknown_fields[0].data, 456)
+    nested_message.ClearField('payload')
+    self.assertEqual(unknown_fields[0].data, 456)
+    unknown_fields = (
+        nested_message.payload.optional_nested_message.UnknownFields())
+    self.assertEqual(0, len(unknown_fields))
+
+  def testUnknownField(self):
+    message = unittest_pb2.TestAllTypes()
+    message.optional_int32 = 123
+    destination = unittest_pb2.TestEmptyMessage()
+    destination.ParseFromString(message.SerializeToString())
+    unknown_field = destination.UnknownFields()[0]
+    destination.Clear()
+    with self.assertRaises(ValueError) as context:
+      unknown_field.data    # pylint: disable=pointless-statement
+    self.assertIn('The parent message might be cleared.',
+                  str(context.exception))
 
   def testUnknownExtensions(self):
     message = unittest_pb2.TestEmptyMessageWithExtensions()
@@ -280,15 +364,13 @@ class UnknownEnumValuesTest(BaseTestCase):
 
   def CheckUnknownField(self, name, expected_value):
     field_descriptor = self.descriptor.fields_by_name[name]
-    wire_type = type_checkers.FIELD_TYPE_TO_WIRE_TYPE[field_descriptor.type]
-    field_tag = encoder.TagBytes(field_descriptor.number, wire_type)
-    result_dict = {}
-    for tag_bytes, value in self.missing_message._unknown_fields:
-      if tag_bytes == field_tag:
-        decoder = missing_enum_values_pb2.TestEnumValues._decoders_by_tag[
-            tag_bytes][0]
-        decoder(value, 0, len(value), self.message, result_dict)
-    self.assertEqual(expected_value, result_dict[field_descriptor])
+    unknown_fields = self.missing_message.UnknownFields()
+    for field in unknown_fields:
+      if field.field_number == field_descriptor.number:
+        if field_descriptor.label == descriptor.FieldDescriptor.LABEL_REPEATED:
+          self.assertIn(field.data, expected_value)
+        else:
+          self.assertEqual(expected_value, field.data)
 
   def testUnknownParseMismatchEnumValue(self):
     just_string = missing_enum_values_pb2.JustString()
@@ -317,7 +399,6 @@ class UnknownEnumValuesTest(BaseTestCase):
   def testUnknownPackedEnumValue(self):
     self.assertEqual([], self.missing_message.packed_nested_enum)
 
-  @SkipCheckUnknownFieldIfCppImplementation
   def testCheckUnknownFieldValueForEnum(self):
     self.CheckUnknownField('optional_nested_enum',
                            self.message.optional_nested_enum)
diff --git a/python/google/protobuf/json_format.py b/python/google/protobuf/json_format.py
index 58c94a47..ce1db7d7 100644
--- a/python/google/protobuf/json_format.py
+++ b/python/google/protobuf/json_format.py
@@ -482,7 +482,7 @@ class _Parser(object):
               ('Message type "{0}" has no field named "{1}".\n'
                ' Available Fields(except extensions): {2}').format(
                    message_descriptor.full_name, name,
-                   message_descriptor.fields))
+                   [f.json_name for f in message_descriptor.fields]))
         if name in names:
           raise ParseError('Message type "{0}" should not have multiple '
                            '"{1}" fields.'.format(
diff --git a/python/google/protobuf/message.py b/python/google/protobuf/message.py
index eeb0d576..eca2e0a9 100755
--- a/python/google/protobuf/message.py
+++ b/python/google/protobuf/message.py
@@ -268,6 +268,10 @@ class Message(object):
   def ClearExtension(self, extension_handle):
     raise NotImplementedError
 
+  def UnknownFields(self):
+    """Returns the UnknownFieldSet."""
+    raise NotImplementedError
+
   def DiscardUnknownFields(self):
     raise NotImplementedError
 
diff --git a/python/google/protobuf/message_factory.py b/python/google/protobuf/message_factory.py
index e4fb065e..f3ab0a55 100644
--- a/python/google/protobuf/message_factory.py
+++ b/python/google/protobuf/message_factory.py
@@ -39,9 +39,18 @@ my_proto_instance = message_classes['some.proto.package.MessageName']()
 
 __author__ = 'matthewtoia@google.com (Matt Toia)'
 
+from google.protobuf.internal import api_implementation
 from google.protobuf import descriptor_pool
 from google.protobuf import message
-from google.protobuf import reflection
+
+if api_implementation.Type() == 'cpp':
+  from google.protobuf.pyext import cpp_message as message_impl
+else:
+  from google.protobuf.internal import python_message as message_impl
+
+
+# The type of all Message classes.
+_GENERATED_PROTOCOL_MESSAGE_TYPE = message_impl.GeneratedProtocolMessageType
 
 
 class MessageFactory(object):
@@ -70,11 +79,11 @@ class MessageFactory(object):
       descriptor_name = descriptor.name
       if str is bytes:  # PY2
         descriptor_name = descriptor.name.encode('ascii', 'ignore')
-      result_class = reflection.GeneratedProtocolMessageType(
+      result_class = _GENERATED_PROTOCOL_MESSAGE_TYPE(
           descriptor_name,
           (message.Message,),
           {'DESCRIPTOR': descriptor, '__module__': None})
-          # If module not set, it wrongly points to the reflection.py module.
+      # If module not set, it wrongly points to message_factory module.
       self._classes[descriptor] = result_class
       for field in descriptor.fields:
         if field.message_type:
diff --git a/python/google/protobuf/proto_api.h b/python/google/protobuf/proto_api.h
index 5c076d23..47edf0ea 100644
--- a/python/google/protobuf/proto_api.h
+++ b/python/google/protobuf/proto_api.h
@@ -42,16 +42,15 @@
 // Then use the methods of the returned class:
 //    py_proto_api->GetMessagePointer(...);
 
-#ifndef PYTHON_GOOGLE_PROTOBUF_PROTO_API_H__
-#define PYTHON_GOOGLE_PROTOBUF_PROTO_API_H__
+#ifndef GOOGLE_PROTOBUF_PYTHON_PROTO_API_H__
+#define GOOGLE_PROTOBUF_PYTHON_PROTO_API_H__
 
 #include <Python.h>
 
+#include <google/protobuf/message.h>
+
 namespace google {
 namespace protobuf {
-
-class Message;
-
 namespace python {
 
 // Note on the implementation:
@@ -89,4 +88,4 @@ inline const char* PyProtoAPICapsuleName() {
 }  // namespace protobuf
 }  // namespace google
 
-#endif  // PYTHON_GOOGLE_PROTOBUF_PROTO_API_H__
+#endif  // GOOGLE_PROTOBUF_PYTHON_PROTO_API_H__
diff --git a/python/google/protobuf/pyext/descriptor.cc b/python/google/protobuf/pyext/descriptor.cc
index 19a1c38a..3cb16b74 100644
--- a/python/google/protobuf/pyext/descriptor.cc
+++ b/python/google/protobuf/pyext/descriptor.cc
@@ -32,8 +32,8 @@
 
 #include <Python.h>
 #include <frameobject.h>
-#include <google/protobuf/stubs/hash.h>
 #include <string>
+#include <unordered_map>
 
 #include <google/protobuf/io/coded_stream.h>
 #include <google/protobuf/descriptor.pb.h>
@@ -44,6 +44,7 @@
 #include <google/protobuf/pyext/message.h>
 #include <google/protobuf/pyext/message_factory.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
+#include <google/protobuf/stubs/hash.h>
 
 #if PY_MAJOR_VERSION >= 3
   #define PyString_FromStringAndSize PyUnicode_FromStringAndSize
@@ -54,10 +55,12 @@
   #if PY_VERSION_HEX < 0x03030000
     #error "Python 3.0 - 3.2 are not supported."
   #endif
-  #define PyString_AsStringAndSize(ob, charpp, sizep) \
-    (PyUnicode_Check(ob)? \
-       ((*(charpp) = const_cast<char*>(PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL? -1: 0): \
-       PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
+#define PyString_AsStringAndSize(ob, charpp, sizep)                           \
+  (PyUnicode_Check(ob) ? ((*(charpp) = const_cast<char*>(                     \
+                               PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL \
+                              ? -1                                            \
+                              : 0)                                            \
+                       : PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
 #endif
 
 namespace google {
@@ -70,7 +73,7 @@ namespace python {
 // released.
 // This is enough to support the "is" operator on live objects.
 // All descriptors are stored here.
-hash_map<const void*, PyObject*> interned_descriptors;
+std::unordered_map<const void*, PyObject*>* interned_descriptors;
 
 PyObject* PyString_FromCppString(const string& str) {
   return PyString_FromStringAndSize(str.c_str(), str.size());
@@ -119,8 +122,10 @@ bool _CalledFromGeneratedFile(int stacklevel) {
     PyErr_Clear();
     return false;
   }
-  if ((filename_size < 3) || (strcmp(&filename[filename_size - 3], ".py") != 0)) {
-    // Cython's stack does not have .py file name and is not at global module scope.
+  if ((filename_size < 3) ||
+      (strcmp(&filename[filename_size - 3], ".py") != 0)) {
+    // Cython's stack does not have .py file name and is not at global module
+    // scope.
     return true;
   }
   if (filename_size < 7) {
@@ -131,7 +136,7 @@ bool _CalledFromGeneratedFile(int stacklevel) {
     // Filename is not ending with _pb2.
     return false;
   }
-  
+
   if (frame->f_globals != frame->f_locals) {
     // Not at global module scope
     return false;
@@ -197,7 +202,7 @@ static PyObject* GetOrBuildOptions(const DescriptorClass *descriptor) {
   // First search in the cache.
   PyDescriptorPool* caching_pool = GetDescriptorPool_FromPool(
       GetFileDescriptor(descriptor)->pool());
-  hash_map<const void*, PyObject*>* descriptor_options =
+  std::unordered_map<const void*, PyObject*>* descriptor_options =
       caching_pool->descriptor_options;
   if (descriptor_options->find(descriptor) != descriptor_options->end()) {
     PyObject *value = (*descriptor_options)[descriptor];
@@ -232,7 +237,7 @@ static PyObject* GetOrBuildOptions(const DescriptorClass *descriptor) {
   if (value == NULL) {
     return NULL;
   }
-  if (!PyObject_TypeCheck(value.get(), &CMessage_Type)) {
+  if (!PyObject_TypeCheck(value.get(), CMessage_Type)) {
       PyErr_Format(PyExc_TypeError, "Invalid class for %s: %s",
                    message_type->full_name().c_str(),
                    Py_TYPE(value.get())->tp_name);
@@ -275,7 +280,7 @@ static PyObject* CopyToPythonProto(const DescriptorClass *descriptor,
   const Descriptor* self_descriptor =
       DescriptorProtoClass::default_instance().GetDescriptor();
   CMessage* message = reinterpret_cast<CMessage*>(target);
-  if (!PyObject_TypeCheck(target, &CMessage_Type) ||
+  if (!PyObject_TypeCheck(target, CMessage_Type) ||
       message->message->GetDescriptor() != self_descriptor) {
     PyErr_Format(PyExc_TypeError, "Not a %s message",
                  self_descriptor->full_name().c_str());
@@ -332,9 +337,9 @@ PyObject* NewInternedDescriptor(PyTypeObject* type,
   }
 
   // See if the object is in the map of interned descriptors
-  hash_map<const void*, PyObject*>::iterator it =
-      interned_descriptors.find(descriptor);
-  if (it != interned_descriptors.end()) {
+  std::unordered_map<const void*, PyObject*>::iterator it =
+      interned_descriptors->find(descriptor);
+  if (it != interned_descriptors->end()) {
     GOOGLE_DCHECK(Py_TYPE(it->second) == type);
     Py_INCREF(it->second);
     return it->second;
@@ -348,7 +353,7 @@ PyObject* NewInternedDescriptor(PyTypeObject* type,
   py_descriptor->descriptor = descriptor;
 
   // and cache it.
-  interned_descriptors.insert(
+  interned_descriptors->insert(
       std::make_pair(descriptor, reinterpret_cast<PyObject*>(py_descriptor)));
 
   // Ensures that the DescriptorPool stays alive.
@@ -370,7 +375,7 @@ PyObject* NewInternedDescriptor(PyTypeObject* type,
 
 static void Dealloc(PyBaseDescriptor* self) {
   // Remove from interned dictionary
-  interned_descriptors.erase(self->descriptor);
+  interned_descriptors->erase(self->descriptor);
   Py_CLEAR(self->pool);
   Py_TYPE(self)->tp_free(reinterpret_cast<PyObject*>(self));
 }
@@ -758,6 +763,11 @@ static PyObject* HasDefaultValue(PyBaseDescriptor *self, void *closure) {
 static PyObject* GetDefaultValue(PyBaseDescriptor *self, void *closure) {
   PyObject *result;
 
+  if (_GetDescriptor(self)->is_repeated()) {
+    return PyList_New(0);
+  }
+
+
   switch (_GetDescriptor(self)->cpp_type()) {
     case FieldDescriptor::CPPTYPE_INT32: {
       int32 value = _GetDescriptor(self)->default_value_int32();
@@ -805,6 +815,10 @@ static PyObject* GetDefaultValue(PyBaseDescriptor *self, void *closure) {
       result = PyInt_FromLong(value->number());
       break;
     }
+    case FieldDescriptor::CPPTYPE_MESSAGE: {
+      Py_RETURN_NONE;
+      break;
+    }
     default:
       PyErr_Format(PyExc_NotImplementedError, "default value for %s",
                    _GetDescriptor(self)->full_name().c_str());
@@ -1919,6 +1933,9 @@ bool InitDescriptor() {
   if (!InitDescriptorMappingTypes())
     return false;
 
+  // Initialize globals defined in this file.
+  interned_descriptors = new std::unordered_map<const void*, PyObject*>;
+
   return true;
 }
 
diff --git a/python/google/protobuf/pyext/descriptor.h b/python/google/protobuf/pyext/descriptor.h
index f081df84..c4dde9e7 100644
--- a/python/google/protobuf/pyext/descriptor.h
+++ b/python/google/protobuf/pyext/descriptor.h
@@ -100,6 +100,6 @@ bool InitDescriptor();
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_DESCRIPTOR_H__
diff --git a/python/google/protobuf/pyext/descriptor_containers.cc b/python/google/protobuf/pyext/descriptor_containers.cc
index 0153664f..d5b5dc68 100644
--- a/python/google/protobuf/pyext/descriptor_containers.cc
+++ b/python/google/protobuf/pyext/descriptor_containers.cc
@@ -33,7 +33,7 @@
 //
 // They avoid the allocation of a full dictionary or a full list: they simply
 // store a pointer to the parent descriptor, use the C++ Descriptor methods (see
-// google/protobuf/descriptor.h) to retrieve other descriptors, and create
+// net/proto2/public/descriptor.h) to retrieve other descriptors, and create
 // Python objects on the fly.
 //
 // The containers fully conform to abc.Mapping and abc.Sequence, and behave just
@@ -64,10 +64,12 @@
   #if PY_VERSION_HEX < 0x03030000
     #error "Python 3.0 - 3.2 are not supported."
   #endif
-  #define PyString_AsStringAndSize(ob, charpp, sizep) \
-    (PyUnicode_Check(ob)? \
-       ((*(charpp) = const_cast<char*>(PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL? -1: 0): \
-       PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
+#define PyString_AsStringAndSize(ob, charpp, sizep)                           \
+  (PyUnicode_Check(ob) ? ((*(charpp) = const_cast<char*>(                     \
+                               PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL \
+                              ? -1                                            \
+                              : 0)                                            \
+                       : PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
 #endif
 
 namespace google {
diff --git a/python/google/protobuf/pyext/descriptor_containers.h b/python/google/protobuf/pyext/descriptor_containers.h
index 83de07b6..4e05c58e 100644
--- a/python/google/protobuf/pyext/descriptor_containers.h
+++ b/python/google/protobuf/pyext/descriptor_containers.h
@@ -104,6 +104,6 @@ PyObject* NewServiceMethodsByName(const ServiceDescriptor* descriptor);
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_DESCRIPTOR_CONTAINERS_H__
diff --git a/python/google/protobuf/pyext/descriptor_database.cc b/python/google/protobuf/pyext/descriptor_database.cc
index daa40cc7..0514b35c 100644
--- a/python/google/protobuf/pyext/descriptor_database.cc
+++ b/python/google/protobuf/pyext/descriptor_database.cc
@@ -70,7 +70,7 @@ static bool GetFileDescriptorProto(PyObject* py_descriptor,
   const Descriptor* filedescriptor_descriptor =
       FileDescriptorProto::default_instance().GetDescriptor();
   CMessage* message = reinterpret_cast<CMessage*>(py_descriptor);
-  if (PyObject_TypeCheck(py_descriptor, &CMessage_Type) &&
+  if (PyObject_TypeCheck(py_descriptor, CMessage_Type) &&
       message->message->GetDescriptor() == filedescriptor_descriptor) {
     // Fast path: Just use the pointer.
     FileDescriptorProto* file_proto =
@@ -143,6 +143,43 @@ bool PyDescriptorDatabase::FindFileContainingExtension(
   return GetFileDescriptorProto(py_descriptor.get(), output);
 }
 
+// Finds the tag numbers used by all known extensions of
+// containing_type, and appends them to output in an undefined
+// order.
+// Python DescriptorDatabases are not required to implement this method.
+bool PyDescriptorDatabase::FindAllExtensionNumbers(
+    const string& containing_type, std::vector<int>* output) {
+  ScopedPyObjectPtr py_method(
+      PyObject_GetAttrString(py_database_, "FindAllExtensionNumbers"));
+  if (py_method == NULL) {
+    // This method is not implemented, returns without error.
+    PyErr_Clear();
+    return false;
+  }
+  ScopedPyObjectPtr py_list(
+      PyObject_CallFunction(py_method.get(), "s#", containing_type.c_str(),
+                            containing_type.size()));
+  if (py_list == NULL) {
+    PyErr_Print();
+    return false;
+  }
+  Py_ssize_t size = PyList_Size(py_list.get());
+  int64 item_value;
+  for (Py_ssize_t i = 0 ; i < size; ++i) {
+    ScopedPyObjectPtr item(PySequence_GetItem(py_list.get(), i));
+    item_value = PyLong_AsLong(item.get());
+    if (item_value < 0) {
+      GOOGLE_LOG(ERROR)
+          << "FindAllExtensionNumbers method did not return "
+          << "valid extension numbers.";
+      PyErr_Print();
+      return false;
+    }
+    output->push_back(item_value);
+  }
+  return true;
+}
+
 }  // namespace python
 }  // namespace protobuf
 }  // namespace google
diff --git a/python/google/protobuf/pyext/descriptor_database.h b/python/google/protobuf/pyext/descriptor_database.h
index fc71c4bc..daf25e0b 100644
--- a/python/google/protobuf/pyext/descriptor_database.h
+++ b/python/google/protobuf/pyext/descriptor_database.h
@@ -63,6 +63,13 @@ class PyDescriptorDatabase : public DescriptorDatabase {
                                    int field_number,
                                    FileDescriptorProto* output);
 
+  // Finds the tag numbers used by all known extensions of
+  // containing_type, and appends them to output in an undefined
+  // order.
+  // Python objects are not required to implement this method.
+  bool FindAllExtensionNumbers(const string& containing_type,
+                               std::vector<int>* output);
+
  private:
   // The python object that implements the database. The reference is owned.
   PyObject* py_database_;
@@ -70,6 +77,6 @@ class PyDescriptorDatabase : public DescriptorDatabase {
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_DESCRIPTOR_DATABASE_H__
diff --git a/python/google/protobuf/pyext/descriptor_pool.cc b/python/google/protobuf/pyext/descriptor_pool.cc
index 962accc6..d0038b10 100644
--- a/python/google/protobuf/pyext/descriptor_pool.cc
+++ b/python/google/protobuf/pyext/descriptor_pool.cc
@@ -30,6 +30,8 @@
 
 // Implements the DescriptorPool, which collects all descriptors.
 
+#include <unordered_map>
+
 #include <Python.h>
 
 #include <google/protobuf/descriptor.pb.h>
@@ -46,10 +48,12 @@
   #if PY_VERSION_HEX < 0x03030000
     #error "Python 3.0 - 3.2 are not supported."
   #endif
-  #define PyString_AsStringAndSize(ob, charpp, sizep) \
-    (PyUnicode_Check(ob)? \
-       ((*(charpp) = const_cast<char*>(PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL? -1: 0): \
-       PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
+#define PyString_AsStringAndSize(ob, charpp, sizep)                           \
+  (PyUnicode_Check(ob) ? ((*(charpp) = const_cast<char*>(                     \
+                               PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL \
+                              ? -1                                            \
+                              : 0)                                            \
+                       : PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
 #endif
 
 namespace google {
@@ -58,7 +62,8 @@ namespace python {
 
 // A map to cache Python Pools per C++ pointer.
 // Pointers are not owned here, and belong to the PyDescriptorPool.
-static hash_map<const DescriptorPool*, PyDescriptorPool*> descriptor_pool_map;
+static std::unordered_map<const DescriptorPool*, PyDescriptorPool*>*
+    descriptor_pool_map;
 
 namespace cdescriptor_pool {
 
@@ -74,8 +79,7 @@ static PyDescriptorPool* _CreateDescriptorPool() {
   cpool->underlay = NULL;
   cpool->database = NULL;
 
-  cpool->descriptor_options =
-      new hash_map<const void*, PyObject *>();
+  cpool->descriptor_options = new std::unordered_map<const void*, PyObject*>();
 
   cpool->py_message_factory = message_factory::NewMessageFactory(
       &PyMessageFactory_Type, cpool);
@@ -101,7 +105,7 @@ static PyDescriptorPool* PyDescriptorPool_NewWithUnderlay(
   cpool->pool = new DescriptorPool(underlay);
   cpool->underlay = underlay;
 
-  if (!descriptor_pool_map.insert(
+  if (!descriptor_pool_map->insert(
       std::make_pair(cpool->pool, cpool)).second) {
     // Should never happen -- would indicate an internal error / bug.
     PyErr_SetString(PyExc_ValueError, "DescriptorPool already registered");
@@ -124,7 +128,7 @@ static PyDescriptorPool* PyDescriptorPool_NewWithDatabase(
     cpool->pool = new DescriptorPool();
   }
 
-  if (!descriptor_pool_map.insert(std::make_pair(cpool->pool, cpool)).second) {
+  if (!descriptor_pool_map->insert(std::make_pair(cpool->pool, cpool)).second) {
     // Should never happen -- would indicate an internal error / bug.
     PyErr_SetString(PyExc_ValueError, "DescriptorPool already registered");
     return NULL;
@@ -151,9 +155,9 @@ static PyObject* New(PyTypeObject* type,
 
 static void Dealloc(PyObject* pself) {
   PyDescriptorPool* self = reinterpret_cast<PyDescriptorPool*>(pself);
-  descriptor_pool_map.erase(self->pool);
+  descriptor_pool_map->erase(self->pool);
   Py_CLEAR(self->py_message_factory);
-  for (hash_map<const void*, PyObject*>::iterator it =
+  for (std::unordered_map<const void*, PyObject*>::iterator it =
            self->descriptor_options->begin();
        it != self->descriptor_options->end(); ++it) {
     Py_DECREF(it->second);
@@ -180,6 +184,7 @@ static PyObject* FindMessageByName(PyObject* self, PyObject* arg) {
     return NULL;
   }
 
+
   return PyMessageDescriptor_FromDescriptor(message_descriptor);
 }
 
@@ -218,6 +223,7 @@ PyObject* FindFieldByName(PyDescriptorPool* self, PyObject* arg) {
     return NULL;
   }
 
+
   return PyFieldDescriptor_FromDescriptor(field_descriptor);
 }
 
@@ -239,6 +245,7 @@ PyObject* FindExtensionByName(PyDescriptorPool* self, PyObject* arg) {
     return NULL;
   }
 
+
   return PyFieldDescriptor_FromDescriptor(field_descriptor);
 }
 
@@ -260,6 +267,7 @@ PyObject* FindEnumTypeByName(PyDescriptorPool* self, PyObject* arg) {
     return NULL;
   }
 
+
   return PyEnumDescriptor_FromDescriptor(enum_descriptor);
 }
 
@@ -281,6 +289,7 @@ PyObject* FindOneofByName(PyDescriptorPool* self, PyObject* arg) {
     return NULL;
   }
 
+
   return PyOneofDescriptor_FromDescriptor(oneof_descriptor);
 }
 
@@ -303,6 +312,7 @@ static PyObject* FindServiceByName(PyObject* self, PyObject* arg) {
     return NULL;
   }
 
+
   return PyServiceDescriptor_FromDescriptor(service_descriptor);
 }
 
@@ -321,6 +331,7 @@ static PyObject* FindMethodByName(PyObject* self, PyObject* arg) {
     return NULL;
   }
 
+
   return PyMethodDescriptor_FromDescriptor(method_descriptor);
 }
 
@@ -339,6 +350,7 @@ static PyObject* FindFileContainingSymbol(PyObject* self, PyObject* arg) {
     return NULL;
   }
 
+
   return PyFileDescriptor_FromDescriptor(file_descriptor);
 }
 
@@ -362,6 +374,7 @@ static PyObject* FindExtensionByNumber(PyObject* self, PyObject* args) {
     return NULL;
   }
 
+
   return PyFieldDescriptor_FromDescriptor(extension_descriptor);
 }
 
@@ -668,13 +681,17 @@ bool InitDescriptorPool() {
   // The Pool of messages declared in Python libraries.
   // generated_pool() contains all messages already linked in C++ libraries, and
   // is used as underlay.
+  descriptor_pool_map =
+      new std::unordered_map<const DescriptorPool*, PyDescriptorPool*>;
   python_generated_pool = cdescriptor_pool::PyDescriptorPool_NewWithUnderlay(
       DescriptorPool::generated_pool());
   if (python_generated_pool == NULL) {
+    delete descriptor_pool_map;
     return false;
   }
+
   // Register this pool to be found for C++-generated descriptors.
-  descriptor_pool_map.insert(
+  descriptor_pool_map->insert(
       std::make_pair(DescriptorPool::generated_pool(),
                      python_generated_pool));
 
@@ -695,9 +712,9 @@ PyDescriptorPool* GetDescriptorPool_FromPool(const DescriptorPool* pool) {
       pool == DescriptorPool::generated_pool()) {
     return python_generated_pool;
   }
-  hash_map<const DescriptorPool*, PyDescriptorPool*>::iterator it =
-      descriptor_pool_map.find(pool);
-  if (it == descriptor_pool_map.end()) {
+  std::unordered_map<const DescriptorPool*, PyDescriptorPool*>::iterator it =
+      descriptor_pool_map->find(pool);
+  if (it == descriptor_pool_map->end()) {
     PyErr_SetString(PyExc_KeyError, "Unknown descriptor pool");
     return NULL;
   }
diff --git a/python/google/protobuf/pyext/descriptor_pool.h b/python/google/protobuf/pyext/descriptor_pool.h
index 53ee53dc..8289daea 100644
--- a/python/google/protobuf/pyext/descriptor_pool.h
+++ b/python/google/protobuf/pyext/descriptor_pool.h
@@ -33,7 +33,7 @@
 
 #include <Python.h>
 
-#include <google/protobuf/stubs/hash.h>
+#include <unordered_map>
 #include <google/protobuf/descriptor.h>
 
 namespace google {
@@ -77,7 +77,7 @@ typedef struct PyDescriptorPool {
   // Cache the options for any kind of descriptor.
   // Descriptor pointers are owned by the DescriptorPool above.
   // Python objects are owned by the map.
-  hash_map<const void*, PyObject*>* descriptor_options;
+  std::unordered_map<const void*, PyObject*>* descriptor_options;
 } PyDescriptorPool;
 
 
@@ -140,6 +140,6 @@ bool InitDescriptorPool();
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_DESCRIPTOR_POOL_H__
diff --git a/python/google/protobuf/pyext/extension_dict.cc b/python/google/protobuf/pyext/extension_dict.cc
index 174c5470..b73368eb 100644
--- a/python/google/protobuf/pyext/extension_dict.cc
+++ b/python/google/protobuf/pyext/extension_dict.cc
@@ -51,10 +51,12 @@
   #if PY_VERSION_HEX < 0x03030000
     #error "Python 3.0 - 3.2 are not supported."
   #endif
-  #define PyString_AsStringAndSize(ob, charpp, sizep) \
-    (PyUnicode_Check(ob)? \
-       ((*(charpp) = const_cast<char*>(PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL? -1: 0): \
-       PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
+#define PyString_AsStringAndSize(ob, charpp, sizep)                           \
+  (PyUnicode_Check(ob) ? ((*(charpp) = const_cast<char*>(                     \
+                               PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL \
+                              ? -1                                            \
+                              : 0)                                            \
+                       : PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
 #endif
 
 namespace google {
@@ -63,40 +65,25 @@ namespace python {
 
 namespace extension_dict {
 
-PyObject* len(ExtensionDict* self) {
-#if PY_MAJOR_VERSION >= 3
-  return PyLong_FromLong(PyDict_Size(self->values));
-#else
-  return PyInt_FromLong(PyDict_Size(self->values));
-#endif
-}
-
 PyObject* subscript(ExtensionDict* self, PyObject* key) {
   const FieldDescriptor* descriptor = cmessage::GetExtensionDescriptor(key);
   if (descriptor == NULL) {
     return NULL;
   }
-  if (!CheckFieldBelongsToMessage(descriptor, self->message)) {
+  if (!CheckFieldBelongsToMessage(descriptor, self->parent->message)) {
     return NULL;
   }
 
   if (descriptor->label() != FieldDescriptor::LABEL_REPEATED &&
       descriptor->cpp_type() != FieldDescriptor::CPPTYPE_MESSAGE) {
-    return cmessage::InternalGetScalar(self->message, descriptor);
+    return cmessage::InternalGetScalar(self->parent->message, descriptor);
   }
 
-  PyObject* value = PyDict_GetItem(self->values, key);
-  if (value != NULL) {
-    Py_INCREF(value);
-    return value;
-  }
-
-  if (self->parent == NULL) {
-    // We are in "detached" state. Don't allow further modifications.
-    // TODO(amauryfa): Support adding non-scalars to a detached extension dict.
-    // This probably requires to store the type of the main message.
-    PyErr_SetObject(PyExc_KeyError, key);
-    return NULL;
+  CMessage::CompositeFieldsMap::iterator iterator =
+      self->parent->composite_fields->find(descriptor);
+  if (iterator != self->parent->composite_fields->end()) {
+    Py_INCREF(iterator->second);
+    return iterator->second;
   }
 
   if (descriptor->label() != FieldDescriptor::LABEL_REPEATED &&
@@ -107,7 +94,8 @@ PyObject* subscript(ExtensionDict* self, PyObject* key) {
     if (sub_message == NULL) {
       return NULL;
     }
-    PyDict_SetItem(self->values, key, sub_message);
+    Py_INCREF(sub_message);
+    (*self->parent->composite_fields)[descriptor] = sub_message;
     return sub_message;
   }
 
@@ -136,7 +124,8 @@ PyObject* subscript(ExtensionDict* self, PyObject* key) {
       if (py_container == NULL) {
         return NULL;
       }
-      PyDict_SetItem(self->values, key, py_container);
+      Py_INCREF(py_container);
+      (*self->parent->composite_fields)[descriptor] = py_container;
       return py_container;
     } else {
       PyObject* py_container = repeated_scalar_container::NewContainer(
@@ -144,7 +133,8 @@ PyObject* subscript(ExtensionDict* self, PyObject* key) {
       if (py_container == NULL) {
         return NULL;
       }
-      PyDict_SetItem(self->values, key, py_container);
+      Py_INCREF(py_container);
+      (*self->parent->composite_fields)[descriptor] = py_container;
       return py_container;
     }
   }
@@ -157,7 +147,7 @@ int ass_subscript(ExtensionDict* self, PyObject* key, PyObject* value) {
   if (descriptor == NULL) {
     return -1;
   }
-  if (!CheckFieldBelongsToMessage(descriptor, self->message)) {
+  if (!CheckFieldBelongsToMessage(descriptor, self->parent->message)) {
     return -1;
   }
 
@@ -167,14 +157,10 @@ int ass_subscript(ExtensionDict* self, PyObject* key, PyObject* value) {
                     "type");
     return -1;
   }
-  if (self->parent) {
-    cmessage::AssureWritable(self->parent);
-    if (cmessage::InternalSetScalar(self->parent, descriptor, value) < 0) {
-      return -1;
-    }
+  cmessage::AssureWritable(self->parent);
+  if (cmessage::InternalSetScalar(self->parent, descriptor, value) < 0) {
+    return -1;
   }
-  // TODO(tibell): We shouldn't write scalars to the cache.
-  PyDict_SetItem(self->values, key, value);
   return 0;
 }
 
@@ -232,22 +218,36 @@ ExtensionDict* NewExtensionDict(CMessage *parent) {
     return NULL;
   }
 
-  self->parent = parent;  // Store a borrowed reference.
-  self->message = parent->message;
-  self->owner = parent->owner;
-  self->values = PyDict_New();
+  Py_INCREF(parent);
+  self->parent = parent;
   return self;
 }
 
 void dealloc(ExtensionDict* self) {
-  Py_CLEAR(self->values);
-  self->owner.reset();
+  Py_CLEAR(self->parent);
   Py_TYPE(self)->tp_free(reinterpret_cast<PyObject*>(self));
 }
 
+static PyObject* RichCompare(ExtensionDict* self, PyObject* other, int opid) {
+  // Only equality comparisons are implemented.
+  if (opid != Py_EQ && opid != Py_NE) {
+    Py_INCREF(Py_NotImplemented);
+    return Py_NotImplemented;
+  }
+  bool equals = false;
+  if (PyObject_TypeCheck(other, &ExtensionDict_Type)) {
+    equals = self->parent == reinterpret_cast<ExtensionDict*>(other)->parent;;
+  }
+  if (equals ^ (opid == Py_EQ)) {
+    Py_RETURN_FALSE;
+  } else {
+    Py_RETURN_TRUE;
+  }
+}
+
 static PyMappingMethods MpMethods = {
-  (lenfunc)len,               /* mp_length */
-  (binaryfunc)subscript,      /* mp_subscript */
+  (lenfunc)NULL,               /* mp_length */
+  (binaryfunc)subscript,       /* mp_subscript */
   (objobjargproc)ass_subscript,/* mp_ass_subscript */
 };
 
@@ -286,7 +286,7 @@ PyTypeObject ExtensionDict_Type = {
   "An extension dict",                 //  tp_doc
   0,                                   //  tp_traverse
   0,                                   //  tp_clear
-  0,                                   //  tp_richcompare
+  (richcmpfunc)extension_dict::RichCompare,  //  tp_richcompare
   0,                                   //  tp_weaklistoffset
   0,                                   //  tp_iter
   0,                                   //  tp_iternext
diff --git a/python/google/protobuf/pyext/extension_dict.h b/python/google/protobuf/pyext/extension_dict.h
index 0de2c4ee..d800d479 100644
--- a/python/google/protobuf/pyext/extension_dict.h
+++ b/python/google/protobuf/pyext/extension_dict.h
@@ -37,6 +37,7 @@
 #include <Python.h>
 
 #include <memory>
+#include <hash_map>
 
 #include <google/protobuf/pyext/message.h>
 
@@ -51,23 +52,8 @@ namespace python {
 typedef struct ExtensionDict {
   PyObject_HEAD;
 
-  // This is the top-level C++ Message object that owns the whole
-  // proto tree.  Every Python container class holds a
-  // reference to it in order to keep it alive as long as there's a
-  // Python object that references any part of the tree.
-  CMessage::OwnerRef owner;
-
-  // Weak reference to parent message. Used to make sure
-  // the parent is writable when an extension field is modified.
+  // Strong, owned reference to the parent message. Never NULL.
   CMessage* parent;
-
-  // Pointer to the C++ Message that this ExtensionDict extends.
-  // Not owned by us.
-  Message* message;
-
-  // A dict of child messages, indexed by Extension descriptors.
-  // Similar to CMessage::composite_fields.
-  PyObject* values;
 } ExtensionDict;
 
 extern PyTypeObject ExtensionDict_Type;
@@ -80,6 +66,6 @@ ExtensionDict* NewExtensionDict(CMessage *parent);
 }  // namespace extension_dict
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_EXTENSION_DICT_H__
diff --git a/python/google/protobuf/pyext/map_container.cc b/python/google/protobuf/pyext/map_container.cc
index 6d7ee285..3eec49c7 100644
--- a/python/google/protobuf/pyext/map_container.cc
+++ b/python/google/protobuf/pyext/map_container.cc
@@ -68,12 +68,14 @@ class MapReflectionFriend {
   static PyObject* MessageMapGetItem(PyObject* _self, PyObject* key);
   static int ScalarMapSetItem(PyObject* _self, PyObject* key, PyObject* v);
   static int MessageMapSetItem(PyObject* _self, PyObject* key, PyObject* v);
+  static PyObject* ScalarMapToStr(PyObject* _self);
+  static PyObject* MessageMapToStr(PyObject* _self);
 };
 
 struct MapIterator {
   PyObject_HEAD;
 
-  std::unique_ptr<::google::protobuf::MapIterator> iter;
+  std::unique_ptr<::proto2::MapIterator> iter;
 
   // A pointer back to the container, so we can notice changes to the version.
   // We own a ref on this.
@@ -199,26 +201,26 @@ static PyObject* MapKeyToPython(const FieldDescriptor* field_descriptor,
 // This is only used for ScalarMap, so we don't need to handle the
 // CPPTYPE_MESSAGE case.
 PyObject* MapValueRefToPython(const FieldDescriptor* field_descriptor,
-                              MapValueRef* value) {
+                              const MapValueRef& value) {
   switch (field_descriptor->cpp_type()) {
     case FieldDescriptor::CPPTYPE_INT32:
-      return PyInt_FromLong(value->GetInt32Value());
+      return PyInt_FromLong(value.GetInt32Value());
     case FieldDescriptor::CPPTYPE_INT64:
-      return PyLong_FromLongLong(value->GetInt64Value());
+      return PyLong_FromLongLong(value.GetInt64Value());
     case FieldDescriptor::CPPTYPE_UINT32:
-      return PyInt_FromSize_t(value->GetUInt32Value());
+      return PyInt_FromSize_t(value.GetUInt32Value());
     case FieldDescriptor::CPPTYPE_UINT64:
-      return PyLong_FromUnsignedLongLong(value->GetUInt64Value());
+      return PyLong_FromUnsignedLongLong(value.GetUInt64Value());
     case FieldDescriptor::CPPTYPE_FLOAT:
-      return PyFloat_FromDouble(value->GetFloatValue());
+      return PyFloat_FromDouble(value.GetFloatValue());
     case FieldDescriptor::CPPTYPE_DOUBLE:
-      return PyFloat_FromDouble(value->GetDoubleValue());
+      return PyFloat_FromDouble(value.GetDoubleValue());
     case FieldDescriptor::CPPTYPE_BOOL:
-      return PyBool_FromLong(value->GetBoolValue());
+      return PyBool_FromLong(value.GetBoolValue());
     case FieldDescriptor::CPPTYPE_STRING:
-      return ToStringObject(field_descriptor, value->GetStringValue());
+      return ToStringObject(field_descriptor, value.GetStringValue());
     case FieldDescriptor::CPPTYPE_ENUM:
-      return PyInt_FromLong(value->GetEnumValue());
+      return PyInt_FromLong(value.GetEnumValue());
     default:
       PyErr_Format(
           PyExc_SystemError, "Couldn't convert type %d to value",
@@ -312,7 +314,7 @@ static MapContainer* GetMap(PyObject* obj) {
 
 Py_ssize_t MapReflectionFriend::Length(PyObject* _self) {
   MapContainer* self = GetMap(_self);
-  const google::protobuf::Message* message = self->message;
+  const proto2::Message* message = self->message;
   return message->GetReflection()->MapSize(*message,
                                            self->parent_field_descriptor);
 }
@@ -421,7 +423,7 @@ int MapContainer::Release() {
 // ScalarMap ///////////////////////////////////////////////////////////////////
 
 PyObject *NewScalarMapContainer(
-    CMessage* parent, const google::protobuf::FieldDescriptor* parent_field_descriptor) {
+    CMessage* parent, const proto2::FieldDescriptor* parent_field_descriptor) {
   if (!CheckFieldBelongsToMessage(parent_field_descriptor, parent->message)) {
     return NULL;
   }
@@ -472,7 +474,7 @@ PyObject* MapReflectionFriend::ScalarMapGetItem(PyObject* _self,
     self->version++;
   }
 
-  return MapValueRefToPython(self->value_field_descriptor, &value);
+  return MapValueRefToPython(self->value_field_descriptor, value);
 }
 
 int MapReflectionFriend::ScalarMapSetItem(PyObject* _self, PyObject* key,
@@ -535,10 +537,47 @@ static PyObject* ScalarMapGet(PyObject* self, PyObject* args) {
   }
 }
 
+PyObject* MapReflectionFriend::ScalarMapToStr(PyObject* _self) {
+  ScopedPyObjectPtr dict(PyDict_New());
+  if (dict == NULL) {
+    return NULL;
+  }
+  ScopedPyObjectPtr key;
+  ScopedPyObjectPtr value;
+
+  MapContainer* self = GetMap(_self);
+  Message* message = self->GetMutableMessage();
+  const Reflection* reflection = message->GetReflection();
+  for (proto2::MapIterator it = reflection->MapBegin(
+           message, self->parent_field_descriptor);
+       it != reflection->MapEnd(message, self->parent_field_descriptor);
+       ++it) {
+    key.reset(MapKeyToPython(self->key_field_descriptor,
+                             it.GetKey()));
+    if (key == NULL) {
+      return NULL;
+    }
+    value.reset(MapValueRefToPython(self->value_field_descriptor,
+                                    it.GetValueRef()));
+    if (value == NULL) {
+      return NULL;
+    }
+    if (PyDict_SetItem(dict.get(), key.get(), value.get()) < 0) {
+      return NULL;
+    }
+  }
+  return PyObject_Repr(dict.get());
+}
+
 static void ScalarMapDealloc(PyObject* _self) {
   MapContainer* self = GetMap(_self);
   self->owner.reset();
-  Py_TYPE(_self)->tp_free(_self);
+  PyTypeObject *type = Py_TYPE(_self);
+  type->tp_free(_self);
+  if (type->tp_flags & Py_TPFLAGS_HEAPTYPE) {
+    // With Python3, the Map class is not static, and must be managed.
+    Py_DECREF(type);
+  }
 }
 
 static PyMethodDef ScalarMapMethods[] = {
@@ -570,6 +609,7 @@ PyTypeObject *ScalarMapContainer_Type;
       {Py_mp_ass_subscript, (void *)MapReflectionFriend::ScalarMapSetItem},
       {Py_tp_methods, (void *)ScalarMapMethods},
       {Py_tp_iter, (void *)MapReflectionFriend::GetIterator},
+      {Py_tp_repr, (void *)MapReflectionFriend::ScalarMapToStr},
       {0, 0},
   };
 
@@ -597,7 +637,7 @@ PyTypeObject *ScalarMapContainer_Type;
     0,                                   //  tp_getattr
     0,                                   //  tp_setattr
     0,                                   //  tp_compare
-    0,                                   //  tp_repr
+    MapReflectionFriend::ScalarMapToStr,  //  tp_repr
     0,                                   //  tp_as_number
     0,                                   //  tp_as_sequence
     &ScalarMapMappingMethods,            //  tp_as_mapping
@@ -634,7 +674,8 @@ static MessageMapContainer* GetMessageMap(PyObject* obj) {
   return reinterpret_cast<MessageMapContainer*>(obj);
 }
 
-static PyObject* GetCMessage(MessageMapContainer* self, Message* message) {
+static PyObject* GetCMessage(MessageMapContainer* self, Message* message,
+                             bool insert_message_dict) {
   // Get or create the CMessage object corresponding to this message.
   ScopedPyObjectPtr key(PyLong_FromVoidPtr(message));
   PyObject* ret = PyDict_GetItem(self->message_dict, key.get());
@@ -649,10 +690,11 @@ static PyObject* GetCMessage(MessageMapContainer* self, Message* message) {
     cmsg->owner = self->owner;
     cmsg->message = message;
     cmsg->parent = self->parent;
-
-    if (PyDict_SetItem(self->message_dict, key.get(), ret) < 0) {
-      Py_DECREF(ret);
-      return NULL;
+    if (insert_message_dict) {
+      if (PyDict_SetItem(self->message_dict, key.get(), ret) < 0) {
+        Py_DECREF(ret);
+        return NULL;
+      }
     }
   } else {
     Py_INCREF(ret);
@@ -662,7 +704,7 @@ static PyObject* GetCMessage(MessageMapContainer* self, Message* message) {
 }
 
 PyObject* NewMessageMapContainer(
-    CMessage* parent, const google::protobuf::FieldDescriptor* parent_field_descriptor,
+    CMessage* parent, const proto2::FieldDescriptor* parent_field_descriptor,
     CMessageClass* message_class) {
   if (!CheckFieldBelongsToMessage(parent_field_descriptor, parent->message)) {
     return NULL;
@@ -781,7 +823,41 @@ PyObject* MapReflectionFriend::MessageMapGetItem(PyObject* _self,
     self->version++;
   }
 
-  return GetCMessage(self, value.MutableMessageValue());
+  return GetCMessage(self, value.MutableMessageValue(), true);
+}
+
+PyObject* MapReflectionFriend::MessageMapToStr(PyObject* _self) {
+  ScopedPyObjectPtr dict(PyDict_New());
+  if (dict == NULL) {
+    return NULL;
+  }
+  ScopedPyObjectPtr key;
+  ScopedPyObjectPtr value;
+
+  MessageMapContainer* self = GetMessageMap(_self);
+  Message* message = self->GetMutableMessage();
+  const Reflection* reflection = message->GetReflection();
+  for (proto2::MapIterator it = reflection->MapBegin(
+           message, self->parent_field_descriptor);
+       it != reflection->MapEnd(message, self->parent_field_descriptor);
+       ++it) {
+    key.reset(MapKeyToPython(self->key_field_descriptor,
+                             it.GetKey()));
+    if (key == NULL) {
+      return NULL;
+    }
+    // Do not insert the cmessage to self->message_dict because
+    // the returned CMessage will not escape this function.
+    value.reset(GetCMessage(
+        self, it.MutableValueRef()->MutableMessageValue(), false));
+    if (value == NULL) {
+      return NULL;
+    }
+    if (PyDict_SetItem(dict.get(), key.get(), value.get()) < 0) {
+      return NULL;
+    }
+  }
+  return PyObject_Repr(dict.get());
 }
 
 PyObject* MessageMapGet(PyObject* self, PyObject* args) {
@@ -813,7 +889,12 @@ static void MessageMapDealloc(PyObject* _self) {
   self->owner.reset();
   Py_DECREF(self->message_dict);
   Py_DECREF(self->message_class);
-  Py_TYPE(_self)->tp_free(_self);
+  PyTypeObject *type = Py_TYPE(_self);
+  type->tp_free(_self);
+  if (type->tp_flags & Py_TPFLAGS_HEAPTYPE) {
+    // With Python3, the Map class is not static, and must be managed.
+    Py_DECREF(type);
+  }
 }
 
 static PyMethodDef MessageMapMethods[] = {
@@ -847,6 +928,7 @@ PyTypeObject *MessageMapContainer_Type;
       {Py_mp_ass_subscript, (void *)MapReflectionFriend::MessageMapSetItem},
       {Py_tp_methods, (void *)MessageMapMethods},
       {Py_tp_iter, (void *)MapReflectionFriend::GetIterator},
+      {Py_tp_repr, (void *)MapReflectionFriend::MessageMapToStr},
       {0, 0}
   };
 
@@ -874,7 +956,7 @@ PyTypeObject *MessageMapContainer_Type;
     0,                                   //  tp_getattr
     0,                                   //  tp_setattr
     0,                                   //  tp_compare
-    0,                                   //  tp_repr
+    MapReflectionFriend::MessageMapToStr,  //  tp_repr
     0,                                   //  tp_as_number
     0,                                   //  tp_as_sequence
     &MessageMapMappingMethods,           //  tp_as_mapping
@@ -929,7 +1011,7 @@ PyObject* MapReflectionFriend::GetIterator(PyObject *_self) {
     Message* message = self->GetMutableMessage();
     const Reflection* reflection = message->GetReflection();
 
-    iter->iter.reset(new ::google::protobuf::MapIterator(
+    iter->iter.reset(new ::proto2::MapIterator(
         reflection->MapBegin(message, self->parent_field_descriptor)));
   }
 
@@ -1027,17 +1109,15 @@ bool InitMapContainers() {
     return false;
   }
 
-  if (!PyObject_TypeCheck(mutable_mapping.get(), &PyType_Type)) {
-    return false;
-  }
-
   Py_INCREF(mutable_mapping.get());
 #if PY_MAJOR_VERSION >= 3
-  PyObject* bases = PyTuple_New(1);
-  PyTuple_SET_ITEM(bases, 0, mutable_mapping.get());
+  ScopedPyObjectPtr bases(PyTuple_Pack(1, mutable_mapping.get()));
+  if (bases == NULL) {
+    return false;
+  }
 
   ScalarMapContainer_Type = reinterpret_cast<PyTypeObject*>(
-      PyType_FromSpecWithBases(&ScalarMapContainer_Type_spec, bases));
+      PyType_FromSpecWithBases(&ScalarMapContainer_Type_spec, bases.get()));
 #else
   _ScalarMapContainer_Type.tp_base =
       reinterpret_cast<PyTypeObject*>(mutable_mapping.get());
@@ -1055,7 +1135,7 @@ bool InitMapContainers() {
 
 #if PY_MAJOR_VERSION >= 3
   MessageMapContainer_Type = reinterpret_cast<PyTypeObject*>(
-      PyType_FromSpecWithBases(&MessageMapContainer_Type_spec, bases));
+      PyType_FromSpecWithBases(&MessageMapContainer_Type_spec, bases.get()));
 #else
   Py_INCREF(mutable_mapping.get());
   _MessageMapContainer_Type.tp_base =
diff --git a/python/google/protobuf/pyext/map_container.h b/python/google/protobuf/pyext/map_container.h
index 111fafbf..7e77b027 100644
--- a/python/google/protobuf/pyext/map_container.h
+++ b/python/google/protobuf/pyext/map_container.h
@@ -120,6 +120,6 @@ extern PyObject* NewMessageMapContainer(
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_MAP_CONTAINER_H__
diff --git a/python/google/protobuf/pyext/message.cc b/python/google/protobuf/pyext/message.cc
index b2984509..5d0e37fa 100644
--- a/python/google/protobuf/pyext/message.cc
+++ b/python/google/protobuf/pyext/message.cc
@@ -45,12 +45,11 @@
 #ifndef Py_TYPE
 #define Py_TYPE(ob) (((PyObject*)(ob))->ob_type)
 #endif
-#include <google/protobuf/descriptor.pb.h>
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/stubs/logging.h>
 #include <google/protobuf/io/coded_stream.h>
 #include <google/protobuf/io/zero_copy_stream_impl_lite.h>
-#include <google/protobuf/util/message_differencer.h>
+#include <google/protobuf/descriptor.pb.h>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/message.h>
 #include <google/protobuf/text_format.h>
@@ -58,12 +57,16 @@
 #include <google/protobuf/pyext/descriptor.h>
 #include <google/protobuf/pyext/descriptor_pool.h>
 #include <google/protobuf/pyext/extension_dict.h>
-#include <google/protobuf/pyext/repeated_composite_container.h>
-#include <google/protobuf/pyext/repeated_scalar_container.h>
+#include <google/protobuf/pyext/field.h>
 #include <google/protobuf/pyext/map_container.h>
 #include <google/protobuf/pyext/message_factory.h>
+#include <google/protobuf/pyext/repeated_composite_container.h>
+#include <google/protobuf/pyext/repeated_scalar_container.h>
+#include <google/protobuf/pyext/unknown_fields.h>
 #include <google/protobuf/pyext/safe_numerics.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
+#include <google/protobuf/util/message_differencer.h>
+#include <google/protobuf/stubs/strutil.h>
 
 #if PY_MAJOR_VERSION >= 3
   #define PyInt_AsLong PyLong_AsLong
@@ -72,16 +75,19 @@
   #define PyString_Check PyUnicode_Check
   #define PyString_FromString PyUnicode_FromString
   #define PyString_FromStringAndSize PyUnicode_FromStringAndSize
+  #define PyString_FromFormat PyUnicode_FromFormat
   #if PY_VERSION_HEX < 0x03030000
     #error "Python 3.0 - 3.2 are not supported."
   #else
   #define PyString_AsString(ob) \
     (PyUnicode_Check(ob)? PyUnicode_AsUTF8(ob): PyBytes_AsString(ob))
-  #define PyString_AsStringAndSize(ob, charpp, sizep) \
-    (PyUnicode_Check(ob)? \
-       ((*(charpp) = const_cast<char*>(PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL? -1: 0): \
-       PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
-  #endif
+#define PyString_AsStringAndSize(ob, charpp, sizep)                           \
+  (PyUnicode_Check(ob) ? ((*(charpp) = const_cast<char*>(                     \
+                               PyUnicode_AsUTF8AndSize(ob, (sizep)))) == NULL \
+                              ? -1                                            \
+                              : 0)                                            \
+                       : PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
+#endif
 #endif
 
 namespace google {
@@ -99,44 +105,27 @@ namespace message_meta {
 static int InsertEmptyWeakref(PyTypeObject* base);
 
 namespace {
-// Copied oveer from internal 'google/protobuf/stubs/strutil.h'.
-inline void UpperString(string * s) {
+// Copied over from internal 'google/protobuf/stubs/strutil.h'.
+inline void LowerString(string * s) {
   string::iterator end = s->end();
   for (string::iterator i = s->begin(); i != end; ++i) {
-    // toupper() changes based on locale.  We don't want this!
-    if ('a' <= *i && *i <= 'z') *i += 'A' - 'a';
+    // tolower() changes based on locale.  We don't want this!
+    if ('A' <= *i && *i <= 'Z') *i += 'a' - 'A';
   }
 }
 }
 
-// Add the number of a field descriptor to the containing message class.
-// Equivalent to:
-//   _cls.<field>_FIELD_NUMBER = <number>
-static bool AddFieldNumberToClass(
-    PyObject* cls, const FieldDescriptor* field_descriptor) {
-  string constant_name = field_descriptor->name() + "_FIELD_NUMBER";
-  UpperString(&constant_name);
-  ScopedPyObjectPtr attr_name(PyString_FromStringAndSize(
-      constant_name.c_str(), constant_name.size()));
-  if (attr_name == NULL) {
-    return false;
-  }
-  ScopedPyObjectPtr number(PyInt_FromLong(field_descriptor->number()));
-  if (number == NULL) {
-    return false;
-  }
-  if (PyObject_SetAttr(cls, attr_name.get(), number.get()) == -1) {
-    return false;
-  }
-  return true;
-}
-
-
 // Finalize the creation of the Message class.
 static int AddDescriptors(PyObject* cls, const Descriptor* descriptor) {
   // For each field set: cls.<field>_FIELD_NUMBER = <number>
   for (int i = 0; i < descriptor->field_count(); ++i) {
-    if (!AddFieldNumberToClass(cls, descriptor->field(i))) {
+    const FieldDescriptor* field_descriptor = descriptor->field(i);
+    ScopedPyObjectPtr property(NewFieldProperty(field_descriptor));
+    if (property == NULL) {
+      return -1;
+    }
+    if (PyObject_SetAttrString(cls, field_descriptor->name().c_str(),
+                               property.get()) < 0) {
       return -1;
     }
   }
@@ -182,7 +171,7 @@ static int AddDescriptors(PyObject* cls, const Descriptor* descriptor) {
   // <message descriptor>.extensions_by_name[name]
   // which was defined previously.
   for (int i = 0; i < descriptor->extension_count(); ++i) {
-    const google::protobuf::FieldDescriptor* field = descriptor->extension(i);
+    const proto2::FieldDescriptor* field = descriptor->extension(i);
     ScopedPyObjectPtr extension_field(PyFieldDescriptor_FromDescriptor(field));
     if (extension_field == NULL) {
       return -1;
@@ -193,11 +182,6 @@ static int AddDescriptors(PyObject* cls, const Descriptor* descriptor) {
             cls, field->name().c_str(), extension_field.get()) == -1) {
       return -1;
     }
-
-    // For each extension set cls.<extension name>_FIELD_NUMBER = <number>.
-    if (!AddFieldNumberToClass(cls, field)) {
-      return -1;
-    }
   }
 
   return 0;
@@ -265,10 +249,10 @@ static PyObject* New(PyTypeObject* type,
   PyObject* well_known_class = PyDict_GetItemString(
       WKT_classes, message_descriptor->full_name().c_str());
   if (well_known_class == NULL) {
-    new_args.reset(Py_BuildValue("s(OO)O", name, &CMessage_Type,
+    new_args.reset(Py_BuildValue("s(OO)O", name, CMessage_Type,
                                  PythonMessage_class, dict));
   } else {
-    new_args.reset(Py_BuildValue("s(OOO)O", name, &CMessage_Type,
+    new_args.reset(Py_BuildValue("s(OOO)O", name, CMessage_Type,
                                  PythonMessage_class, well_known_class, dict));
   }
 
@@ -285,7 +269,7 @@ static PyObject* New(PyTypeObject* type,
   // Insert the empty weakref into the base classes.
   if (InsertEmptyWeakref(
           reinterpret_cast<PyTypeObject*>(PythonMessage_class)) < 0 ||
-      InsertEmptyWeakref(&CMessage_Type) < 0) {
+      InsertEmptyWeakref(CMessage_Type) < 0) {
     return NULL;
   }
 
@@ -353,6 +337,13 @@ static int InsertEmptyWeakref(PyTypeObject *base_type) {
 // The _extensions_by_name dictionary is built on every access.
 // TODO(amauryfa): Migrate all users to pool.FindAllExtensions()
 static PyObject* GetExtensionsByName(CMessageClass *self, void *closure) {
+  if (self->message_descriptor == NULL) {
+    // This is the base Message object, simply raise AttributeError.
+    PyErr_SetString(PyExc_AttributeError,
+                    "Base Message class has no DESCRIPTOR");
+    return NULL;
+  }
+
   const PyDescriptorPool* pool = self->py_message_factory->pool;
 
   std::vector<const FieldDescriptor*> extensions;
@@ -376,6 +367,13 @@ static PyObject* GetExtensionsByName(CMessageClass *self, void *closure) {
 // The _extensions_by_number dictionary is built on every access.
 // TODO(amauryfa): Migrate all users to pool.FindExtensionByNumber()
 static PyObject* GetExtensionsByNumber(CMessageClass *self, void *closure) {
+  if (self->message_descriptor == NULL) {
+    // This is the base Message object, simply raise AttributeError.
+    PyErr_SetString(PyExc_AttributeError,
+                    "Base Message class has no DESCRIPTOR");
+    return NULL;
+  }
+
   const PyDescriptorPool* pool = self->py_message_factory->pool;
 
   std::vector<const FieldDescriptor*> extensions;
@@ -405,9 +403,51 @@ static PyGetSetDef Getters[] = {
   {NULL}
 };
 
+// Compute some class attributes on the fly:
+// - All the _FIELD_NUMBER attributes, for all fields and nested extensions.
+// Returns a new reference, or NULL with an exception set.
+static PyObject* GetClassAttribute(CMessageClass *self, PyObject* name) {
+  char* attr;
+  Py_ssize_t attr_size;
+  static const char kSuffix[] = "_FIELD_NUMBER";
+  if (PyString_AsStringAndSize(name, &attr, &attr_size) >= 0 &&
+      strings::EndsWith(StringPiece(attr, attr_size), kSuffix)) {
+    string field_name(attr, attr_size - sizeof(kSuffix) + 1);
+    LowerString(&field_name);
+
+    // Try to find a field with the given name, without the suffix.
+    const FieldDescriptor* field =
+        self->message_descriptor->FindFieldByLowercaseName(field_name);
+    if (!field) {
+      // Search nested extensions as well.
+      field =
+          self->message_descriptor->FindExtensionByLowercaseName(field_name);
+    }
+    if (field) {
+      return PyInt_FromLong(field->number());
+    }
+  }
+  PyErr_SetObject(PyExc_AttributeError, name);
+  return NULL;
+}
+
+static PyObject* GetAttr(CMessageClass* self, PyObject* name) {
+  PyObject* result = CMessageClass_Type->tp_base->tp_getattro(
+      reinterpret_cast<PyObject*>(self), name);
+  if (result != NULL) {
+    return result;
+  }
+  if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
+    return NULL;
+  }
+
+  PyErr_Clear();
+  return GetClassAttribute(self, name);
+}
+
 }  // namespace message_meta
 
-PyTypeObject CMessageClass_Type = {
+static PyTypeObject _CMessageClass_Type = {
   PyVarObject_HEAD_INIT(&PyType_Type, 0)
   FULL_MODULE_NAME ".MessageMeta",     // tp_name
   sizeof(CMessageClass),               // tp_basicsize
@@ -424,7 +464,7 @@ PyTypeObject CMessageClass_Type = {
   0,                                   // tp_hash
   0,                                   // tp_call
   0,                                   // tp_str
-  0,                                   // tp_getattro
+  (getattrofunc)message_meta::GetAttr,  // tp_getattro
   0,                                   // tp_setattro
   0,                                   // tp_as_buffer
   Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  // tp_flags
@@ -447,9 +487,10 @@ PyTypeObject CMessageClass_Type = {
   0,                                   // tp_alloc
   message_meta::New,                   // tp_new
 };
+PyTypeObject* CMessageClass_Type = &_CMessageClass_Type;
 
 static CMessageClass* CheckMessageClass(PyTypeObject* cls) {
-  if (!PyObject_TypeCheck(cls, &CMessageClass_Type)) {
+  if (!PyObject_TypeCheck(cls, CMessageClass_Type)) {
     PyErr_Format(PyExc_TypeError, "Class %s is not a Message", cls->tp_name);
     return NULL;
   }
@@ -487,10 +528,20 @@ struct ChildVisitor {
   }
 
   // Returns 0 on success, -1 on failure.
+  int VisitMapContainer(MapContainer* container) {
+    return 0;
+  }
+
+  // Returns 0 on success, -1 on failure.
   int VisitCMessage(CMessage* cmessage,
                     const FieldDescriptor* field_descriptor) {
     return 0;
   }
+
+  // Returns 0 on success, -1 on failure.
+  int VisitUnknownFieldSet(PyUnknownFields* unknown_field_set) {
+    return 0;
+  }
 };
 
 // Apply a function to a composite field.  Does nothing if child is of
@@ -538,34 +589,19 @@ int ForEachCompositeField(CMessage* self, Visitor visitor) {
 
   // Visit normal fields.
   if (self->composite_fields) {
-    // Never use self->message in this function, it may be already freed.
-    const Descriptor* message_descriptor =
-        GetMessageDescriptor(Py_TYPE(self));
-    while (PyDict_Next(self->composite_fields, &pos, &key, &field)) {
-      Py_ssize_t key_str_size;
-      char *key_str_data;
-      if (PyString_AsStringAndSize(key, &key_str_data, &key_str_size) != 0)
-        return -1;
-      const string key_str(key_str_data, key_str_size);
-      const FieldDescriptor* descriptor =
-        message_descriptor->FindFieldByName(key_str);
-      if (descriptor != NULL) {
-        if (VisitCompositeField(descriptor, field, visitor) == -1)
-          return -1;
-      }
+    for (CMessage::CompositeFieldsMap::iterator it =
+             self->composite_fields->begin();
+         it != self->composite_fields->end(); it++) {
+      const FieldDescriptor* descriptor = it->first;
+      PyObject* field = it->second;
+      if (VisitCompositeField(descriptor, field, visitor) == -1) return -1;
     }
   }
 
-  // Visit extension fields.
-  if (self->extensions != NULL) {
-    pos = 0;
-    while (PyDict_Next(self->extensions->values, &pos, &key, &field)) {
-      const FieldDescriptor* descriptor = cmessage::GetExtensionDescriptor(key);
-      if (descriptor == NULL)
-        return -1;
-      if (VisitCompositeField(descriptor, field, visitor) == -1)
-        return -1;
-    }
+  if (self->unknown_field_set) {
+    PyUnknownFields* unknown_field_set =
+      reinterpret_cast<PyUnknownFields*>(self->unknown_field_set);
+    visitor.VisitUnknownFieldSet(unknown_field_set);
   }
 
   return 0;
@@ -577,8 +613,12 @@ PyObject* EncodeError_class;
 PyObject* DecodeError_class;
 PyObject* PickleError_class;
 
-/* Is 64bit */
+// Format an error message for unexpected types.
+// Always return with an exception set.
 void FormatTypeError(PyObject* arg, char* expected_types) {
+  // This function is often called with an exception set.
+  // Clear it to call PyObject_Repr() in good conditions.
+  PyErr_Clear();
   PyObject* repr = PyObject_Repr(arg);
   if (repr) {
     PyErr_Format(PyExc_TypeError,
@@ -859,7 +899,7 @@ bool CheckFieldBelongsToMessage(const FieldDescriptor* field_descriptor,
 namespace cmessage {
 
 PyMessageFactory* GetFactoryForMessage(CMessage* message) {
-  GOOGLE_DCHECK(PyObject_TypeCheck(message, &CMessage_Type));
+  GOOGLE_DCHECK(PyObject_TypeCheck(message, CMessage_Type));
   return reinterpret_cast<CMessageClass*>(Py_TYPE(message))->py_message_factory;
 }
 
@@ -883,22 +923,20 @@ static int MaybeReleaseOverlappingOneofField(
     // Non-message fields don't need to be released.
     return 0;
   }
-  const char* field_name = existing_field->name().c_str();
-  PyObject* child_message = cmessage->composite_fields ?
-      PyDict_GetItemString(cmessage->composite_fields, field_name) : NULL;
-  if (child_message == NULL) {
-    // No python reference to this field so no need to release.
-    return 0;
-  }
-
-  if (InternalReleaseFieldByDescriptor(
-          cmessage, existing_field, child_message) < 0) {
-    return -1;
+  if (cmessage->composite_fields) {
+    CMessage::CompositeFieldsMap::iterator iterator =
+        cmessage->composite_fields->find(existing_field);
+    if (iterator != cmessage->composite_fields->end()) {
+      if (InternalReleaseFieldByDescriptor(cmessage, existing_field,
+                                           iterator->second) < 0) {
+        return -1;
+      }
+      Py_DECREF(iterator->second);
+      cmessage->composite_fields->erase(iterator);
+    }
   }
-  return PyDict_DelItemString(cmessage->composite_fields, field_name);
-#else
-  return 0;
 #endif
+  return 0;
 }
 
 // ---------------------------------------------------------------------
@@ -937,10 +975,49 @@ struct FixupMessageReference : public ChildVisitor {
     return 0;
   }
 
+  int VisitUnknownFieldSet(PyUnknownFields* unknown_field_set) {
+    const Reflection* reflection = message_->GetReflection();
+    unknown_field_set->fields = &reflection->GetUnknownFields(*message_);
+    return 0;
+  }
+
  private:
   Message* message_;
 };
 
+// After a Merge, visit every sub-message that was read-only, and
+// eventually update their pointer if the Merge operation modified them.
+struct FixupMessageAfterMerge : public FixupMessageReference {
+  explicit FixupMessageAfterMerge(CMessage* parent) :
+      FixupMessageReference(parent->message),
+      parent_cmessage(parent), message(parent->message) {}
+
+  int VisitCMessage(CMessage* cmessage,
+                    const FieldDescriptor* field_descriptor) {
+    if (cmessage->read_only == false) {
+      return 0;
+    }
+    if (message->GetReflection()->HasField(*message, field_descriptor)) {
+      Message* mutable_message = GetMutableMessage(
+          parent_cmessage, field_descriptor);
+      if (mutable_message == NULL) {
+        return -1;
+      }
+      cmessage->message = mutable_message;
+      cmessage->read_only = false;
+      if (ForEachCompositeField(
+              cmessage, FixupMessageAfterMerge(cmessage)) == -1) {
+        return -1;
+      }
+    }
+    return 0;
+  }
+
+ private:
+  CMessage* parent_cmessage;
+  Message* message;
+};
+
 int AssureWritable(CMessage* self) {
   if (self == NULL || !self->read_only) {
     return 0;
@@ -974,10 +1051,8 @@ int AssureWritable(CMessage* self) {
   // When a CMessage is made writable its Message pointer is updated
   // to point to a new mutable Message.  When that happens we need to
   // update any references to the old, read-only CMessage.  There are
-  // four places such references occur: RepeatedScalarContainer,
-  // RepeatedCompositeContainer, MapContainer, and ExtensionDict.
-  if (self->extensions != NULL)
-    self->extensions->message = self->message;
+  // three places such references occur: RepeatedScalarContainer,
+  // RepeatedCompositeContainer, and MapContainer.
   if (ForEachCompositeField(self, FixupMessageReference(self->message)) == -1)
     return -1;
 
@@ -986,27 +1061,6 @@ int AssureWritable(CMessage* self) {
 
 // --- Globals:
 
-// Retrieve a C++ FieldDescriptor for a message attribute.
-// The C++ message must be valid.
-// TODO(amauryfa): This function should stay internal, because exception
-// handling is not consistent.
-static const FieldDescriptor* GetFieldDescriptor(
-    CMessage* self, PyObject* name) {
-  const Descriptor *message_descriptor = self->message->GetDescriptor();
-  char* field_name;
-  Py_ssize_t size;
-  if (PyString_AsStringAndSize(name, &field_name, &size) < 0) {
-    return NULL;
-  }
-  const FieldDescriptor *field_descriptor =
-      message_descriptor->FindFieldByName(string(field_name, size));
-  if (field_descriptor == NULL) {
-    // Note: No exception is set!
-    return NULL;
-  }
-  return field_descriptor;
-}
-
 // Retrieve a C++ FieldDescriptor for an extension handle.
 const FieldDescriptor* GetExtensionDescriptor(PyObject* extension) {
   ScopedPyObjectPtr cdescriptor;
@@ -1038,7 +1092,7 @@ static PyObject* GetIntegerEnumValue(const FieldDescriptor& descriptor,
     const EnumValueDescriptor* enum_value_descriptor =
         enum_descriptor->FindValueByName(string(enum_label, size));
     if (enum_value_descriptor == NULL) {
-      PyErr_SetString(PyExc_ValueError, "unknown enum label");
+      PyErr_Format(PyExc_ValueError, "unknown enum label \"%s\"", enum_label);
       return NULL;
     }
     return PyInt_FromLong(enum_value_descriptor->number());
@@ -1164,19 +1218,24 @@ int InitAttributes(CMessage* self, PyObject* args, PyObject* kwargs) {
       PyErr_SetString(PyExc_ValueError, "Field name must be a string");
       return -1;
     }
-    const FieldDescriptor* descriptor = GetFieldDescriptor(self, name);
-    if (descriptor == NULL) {
+    ScopedPyObjectPtr property(
+        PyObject_GetAttr(reinterpret_cast<PyObject*>(Py_TYPE(self)), name));
+    if (property == NULL ||
+        !PyObject_TypeCheck(property.get(), CFieldProperty_Type)) {
       PyErr_Format(PyExc_ValueError, "Protocol message %s has no \"%s\" field.",
                    self->message->GetDescriptor()->name().c_str(),
                    PyString_AsString(name));
       return -1;
     }
+    const FieldDescriptor* descriptor =
+        reinterpret_cast<PyMessageFieldProperty*>(property.get())
+            ->field_descriptor;
     if (value == Py_None) {
       // field=None is the same as no field at all.
       continue;
     }
     if (descriptor->is_map()) {
-      ScopedPyObjectPtr map(GetAttr(reinterpret_cast<PyObject*>(self), name));
+      ScopedPyObjectPtr map(GetFieldValue(self, descriptor));
       const FieldDescriptor* value_descriptor =
           descriptor->message_type()->FindFieldByName("value");
       if (value_descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
@@ -1204,8 +1263,7 @@ int InitAttributes(CMessage* self, PyObject* args, PyObject* kwargs) {
         }
       }
     } else if (descriptor->label() == FieldDescriptor::LABEL_REPEATED) {
-      ScopedPyObjectPtr container(
-          GetAttr(reinterpret_cast<PyObject*>(self), name));
+      ScopedPyObjectPtr container(GetFieldValue(self, descriptor));
       if (container == NULL) {
         return -1;
       }
@@ -1272,8 +1330,7 @@ int InitAttributes(CMessage* self, PyObject* args, PyObject* kwargs) {
         }
       }
     } else if (descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-      ScopedPyObjectPtr message(
-          GetAttr(reinterpret_cast<PyObject*>(self), name));
+      ScopedPyObjectPtr message(GetFieldValue(self, descriptor));
       if (message == NULL) {
         return -1;
       }
@@ -1297,9 +1354,9 @@ int InitAttributes(CMessage* self, PyObject* args, PyObject* kwargs) {
         if (new_val == NULL) {
           return -1;
         }
+        value = new_val.get();
       }
-      if (SetAttr(reinterpret_cast<PyObject*>(self), name,
-                  (new_val.get() == NULL) ? value : new_val.get()) < 0) {
+      if (SetFieldValue(self, descriptor, value) < 0) {
         return -1;
       }
     }
@@ -1322,10 +1379,11 @@ CMessage* NewEmptyMessage(CMessageClass* type) {
   self->parent = NULL;
   self->parent_field_descriptor = NULL;
   self->read_only = false;
-  self->extensions = NULL;
 
   self->composite_fields = NULL;
 
+  self->unknown_field_set = NULL;
+
   return self;
 }
 
@@ -1408,12 +1466,20 @@ static void Dealloc(CMessage* self) {
   }
   // Null out all weak references from children to this message.
   GOOGLE_CHECK_EQ(0, ForEachCompositeField(self, ClearWeakReferences()));
-  if (self->extensions) {
-    self->extensions->parent = NULL;
-  }
 
-  Py_CLEAR(self->extensions);
-  Py_CLEAR(self->composite_fields);
+  if (self->composite_fields) {
+    for (CMessage::CompositeFieldsMap::iterator it =
+             self->composite_fields->begin();
+         it != self->composite_fields->end(); it++) {
+      Py_DECREF(it->second);
+    }
+    delete self->composite_fields;
+  }
+  if (self->unknown_field_set) {
+    unknown_fields::Clear(
+        reinterpret_cast<PyUnknownFields*>(self->unknown_field_set));
+    Py_CLEAR(self->unknown_field_set);
+  }
   self->owner.~ThreadUnsafeSharedPtr<Message>();
   Py_TYPE(self)->tp_free(reinterpret_cast<PyObject*>(self));
 }
@@ -1564,13 +1630,16 @@ PyObject* ClearExtension(CMessage* self, PyObject* extension) {
   if (descriptor == NULL) {
     return NULL;
   }
-  if (self->extensions != NULL) {
-    PyObject* value = PyDict_GetItem(self->extensions->values, extension);
-    if (value != NULL) {
-      if (InternalReleaseFieldByDescriptor(self, descriptor, value) < 0) {
+  if (self->composite_fields != NULL) {
+    CMessage::CompositeFieldsMap::iterator iterator =
+        self->composite_fields->find(descriptor);
+    if (iterator != self->composite_fields->end()) {
+      if (InternalReleaseFieldByDescriptor(self, descriptor,
+                                           iterator->second) < 0) {
         return NULL;
       }
-      PyDict_DelItem(self->extensions->values, extension);
+      Py_DECREF(iterator->second);
+      self->composite_fields->erase(iterator);
     }
   }
   return ClearFieldByDescriptor(self, descriptor);
@@ -1770,14 +1839,16 @@ PyObject* ClearField(CMessage* self, PyObject* arg) {
     arg = arg_in_oneof.get();
   }
 
-  // Release the field if it exists in the dict of composite fields.
   if (self->composite_fields) {
-    PyObject* value = PyDict_GetItem(self->composite_fields, arg);
-    if (value != NULL) {
-      if (InternalReleaseFieldByDescriptor(self, field_descriptor, value) < 0) {
+    CMessage::CompositeFieldsMap::iterator iterator =
+        self->composite_fields->find(field_descriptor);
+    if (iterator != self->composite_fields->end()) {
+      if (InternalReleaseFieldByDescriptor(self, field_descriptor,
+                                           iterator->second) < 0) {
         return NULL;
       }
-      PyDict_DelItem(self->composite_fields, arg);
+      Py_DECREF(iterator->second);
+      self->composite_fields->erase(iterator);
     }
   }
   return ClearFieldByDescriptor(self, field_descriptor);
@@ -1787,9 +1858,18 @@ PyObject* Clear(CMessage* self) {
   AssureWritable(self);
   if (ForEachCompositeField(self, ReleaseChild(self)) == -1)
     return NULL;
-  Py_CLEAR(self->extensions);
   if (self->composite_fields) {
-    PyDict_Clear(self->composite_fields);
+    for (CMessage::CompositeFieldsMap::iterator it =
+             self->composite_fields->begin();
+         it != self->composite_fields->end(); it++) {
+      Py_DECREF(it->second);
+    }
+    self->composite_fields->clear();
+  }
+  if (self->unknown_field_set) {
+    unknown_fields::Clear(
+        reinterpret_cast<PyUnknownFields*>(self->unknown_field_set));
+    Py_CLEAR(self->unknown_field_set);
   }
   self->message->Clear();
   Py_RETURN_NONE;
@@ -1946,7 +2026,7 @@ static PyObject* ToStr(CMessage* self) {
 
 PyObject* MergeFrom(CMessage* self, PyObject* arg) {
   CMessage* other_message;
-  if (!PyObject_TypeCheck(arg, &CMessage_Type)) {
+  if (!PyObject_TypeCheck(arg, CMessage_Type)) {
     PyErr_Format(PyExc_TypeError,
                  "Parameter to MergeFrom() must be instance of same class: "
                  "expected %s got %s.",
@@ -1967,18 +2047,19 @@ PyObject* MergeFrom(CMessage* self, PyObject* arg) {
   }
   AssureWritable(self);
 
-  // TODO(tibell): Message::MergeFrom might turn some child Messages
-  // into mutable messages, invalidating the message field in the
-  // corresponding CMessages.  We should run a FixupMessageReferences
-  // pass here.
-
   self->message->MergeFrom(*other_message->message);
+  // Child message might be lazily created before MergeFrom. Make sure they
+  // are mutable at this point if child messages are really created.
+  if (ForEachCompositeField(self, FixupMessageAfterMerge(self)) == -1) {
+    return NULL;
+  }
+
   Py_RETURN_NONE;
 }
 
 static PyObject* CopyFrom(CMessage* self, PyObject* arg) {
   CMessage* other_message;
-  if (!PyObject_TypeCheck(arg, &CMessage_Type)) {
+  if (!PyObject_TypeCheck(arg, CMessage_Type)) {
     PyErr_Format(PyExc_TypeError,
                  "Parameter to CopyFrom() must be instance of same class: "
                  "expected %s got %s.",
@@ -2050,6 +2131,7 @@ static PyObject* MergeFromString(CMessage* self, PyObject* arg) {
   }
 
   AssureWritable(self);
+
   io::CodedInputStream input(
       reinterpret_cast<const uint8*>(data), data_length);
   if (allow_oversize_protos) {
@@ -2058,6 +2140,12 @@ static PyObject* MergeFromString(CMessage* self, PyObject* arg) {
   PyMessageFactory* factory = GetFactoryForMessage(self);
   input.SetExtensionRegistry(factory->pool->pool, factory->message_factory);
   bool success = self->message->MergePartialFromCodedStream(&input);
+  // Child message might be lazily created before MergeFrom. Make sure they
+  // are mutable at this point if child messages are really created.
+  if (ForEachCompositeField(self, FixupMessageAfterMerge(self)) == -1) {
+    return NULL;
+  }
+
   if (success) {
     if (!input.ConsumedEntireMessage()) {
       // TODO(jieluo): Raise error and return NULL instead.
@@ -2088,7 +2176,7 @@ PyObject* RegisterExtension(PyObject* cls, PyObject* extension_handle) {
   if (descriptor == NULL) {
     return NULL;
   }
-  if (!PyObject_TypeCheck(cls, &CMessageClass_Type)) {
+  if (!PyObject_TypeCheck(cls, CMessageClass_Type)) {
     PyErr_Format(PyExc_TypeError, "Expected a message class, got %s",
                  cls->ob_type->tp_name);
     return NULL;
@@ -2192,23 +2280,15 @@ static PyObject* ListFields(CMessage* self) {
       PyTuple_SET_ITEM(t.get(), 1, extension);
     } else {
       // Normal field
-      const string& field_name = fields[i]->name();
-      ScopedPyObjectPtr py_field_name(PyString_FromStringAndSize(
-          field_name.c_str(), field_name.length()));
-      if (py_field_name == NULL) {
-        PyErr_SetString(PyExc_ValueError, "bad string");
-        return NULL;
-      }
       ScopedPyObjectPtr field_descriptor(
           PyFieldDescriptor_FromDescriptor(fields[i]));
       if (field_descriptor == NULL) {
         return NULL;
       }
 
-      PyObject* field_value =
-          GetAttr(reinterpret_cast<PyObject*>(self), py_field_name.get());
+      PyObject* field_value = GetFieldValue(self, fields[i]);
       if (field_value == NULL) {
-        PyErr_SetObject(PyExc_ValueError, py_field_name.get());
+        PyErr_SetString(PyExc_ValueError, fields[i]->name().c_str());
         return NULL;
       }
       PyTuple_SET_ITEM(t.get(), 0, field_descriptor.release());
@@ -2261,10 +2341,10 @@ static PyObject* RichCompare(CMessage* self, PyObject* other, int opid) {
   }
   bool equals = true;
   // If other is not a message, it cannot be equal.
-  if (!PyObject_TypeCheck(other, &CMessage_Type)) {
+  if (!PyObject_TypeCheck(other, CMessage_Type)) {
     equals = false;
   }
-  const google::protobuf::Message* other_message =
+  const proto2::Message* other_message =
       reinterpret_cast<CMessage*>(other)->message;
   // If messages don't have the same descriptors, they are not equal.
   if (equals &&
@@ -2272,11 +2352,12 @@ static PyObject* RichCompare(CMessage* self, PyObject* other, int opid) {
     equals = false;
   }
   // Check the message contents.
-  if (equals && !google::protobuf::util::MessageDifferencer::Equals(
+  if (equals && !proto2::util::MessageDifferencer::Equals(
           *self->message,
           *reinterpret_cast<CMessage*>(other)->message)) {
     equals = false;
   }
+
   if (equals ^ (opid == Py_EQ)) {
     Py_RETURN_FALSE;
   } else {
@@ -2498,7 +2579,7 @@ PyObject* DeepCopy(CMessage* self, PyObject* arg) {
   if (clone == NULL) {
     return NULL;
   }
-  if (!PyObject_TypeCheck(clone, &CMessage_Type)) {
+  if (!PyObject_TypeCheck(clone, CMessage_Type)) {
     Py_DECREF(clone);
     return NULL;
   }
@@ -2592,26 +2673,29 @@ PyObject* _CheckCalledFromGeneratedFile(PyObject* unused,
 }
 
 static PyObject* GetExtensionDict(CMessage* self, void *closure) {
-  if (self->extensions)  {
-    Py_INCREF(self->extensions);
-    return reinterpret_cast<PyObject*>(self->extensions);
-  }
-
   // If there are extension_ranges, the message is "extendable". Allocate a
   // dictionary to store the extension fields.
   const Descriptor* descriptor = GetMessageDescriptor(Py_TYPE(self));
-  if (descriptor->extension_range_count() > 0) {
-    ExtensionDict* extension_dict = extension_dict::NewExtensionDict(self);
-    if (extension_dict == NULL) {
-      return NULL;
-    }
-    self->extensions = extension_dict;
-    Py_INCREF(self->extensions);
-    return reinterpret_cast<PyObject*>(self->extensions);
+  if (!descriptor->extension_range_count()) {
+    PyErr_SetNone(PyExc_AttributeError);
+    return NULL;
+  }
+  if (!self->composite_fields) {
+    self->composite_fields = new CMessage::CompositeFieldsMap();
   }
+  if (!self->composite_fields) {
+    return NULL;
+  }
+  ExtensionDict* extension_dict = extension_dict::NewExtensionDict(self);
+  return reinterpret_cast<PyObject*>(extension_dict);
+}
 
-  PyErr_SetNone(PyExc_AttributeError);
-  return NULL;
+static PyObject* UnknownFieldSet(CMessage* self) {
+  if (self->unknown_field_set == NULL) {
+    self->unknown_field_set = unknown_fields::NewPyUnknownFields(self);
+  }
+  Py_INCREF(self->unknown_field_set);
+  return self->unknown_field_set;
 }
 
 static PyObject* GetExtensionsByName(CMessage *self, void *closure) {
@@ -2682,6 +2766,8 @@ static PyMethodDef Methods[] = {
     "Serializes the message to a string, only for initialized messages." },
   { "SetInParent", (PyCFunction)SetInParent, METH_NOARGS,
     "Sets the has bit of the given field in its parent message." },
+  { "UnknownFields", (PyCFunction)UnknownFieldSet, METH_NOARGS,
+    "Parse unknown field set"},
   { "WhichOneof", (PyCFunction)WhichOneof, METH_O,
     "Returns the name of the field set inside a oneof, "
     "or None if no field is set." },
@@ -2693,30 +2779,53 @@ static PyMethodDef Methods[] = {
   { NULL, NULL}
 };
 
-static bool SetCompositeField(
-    CMessage* self, PyObject* name, PyObject* value) {
+static bool SetCompositeField(CMessage* self, const FieldDescriptor* field,
+                              PyObject* value) {
   if (self->composite_fields == NULL) {
-    self->composite_fields = PyDict_New();
-    if (self->composite_fields == NULL) {
-      return false;
-    }
+    self->composite_fields = new CMessage::CompositeFieldsMap();
   }
-  return PyDict_SetItem(self->composite_fields, name, value) == 0;
+  Py_INCREF(value);
+  Py_XDECREF((*self->composite_fields)[field]);
+  (*self->composite_fields)[field] = value;
+  return true;
 }
 
 PyObject* GetAttr(PyObject* pself, PyObject* name) {
   CMessage* self = reinterpret_cast<CMessage*>(pself);
-  PyObject* value = self->composite_fields ?
-      PyDict_GetItem(self->composite_fields, name) : NULL;
-  if (value != NULL) {
-    Py_INCREF(value);
-    return value;
+  PyObject* result = PyObject_GenericGetAttr(
+      reinterpret_cast<PyObject*>(self), name);
+  if (result != NULL) {
+    return result;
+  }
+  if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
+    return NULL;
   }
 
-  const FieldDescriptor* field_descriptor = GetFieldDescriptor(self, name);
-  if (field_descriptor == NULL) {
-    return CMessage_Type.tp_base->tp_getattro(
-        reinterpret_cast<PyObject*>(self), name);
+  PyErr_Clear();
+  return message_meta::GetClassAttribute(
+      CheckMessageClass(Py_TYPE(self)), name);
+}
+
+PyObject* GetFieldValue(CMessage* self,
+                        const FieldDescriptor* field_descriptor) {
+  if (self->composite_fields) {
+    CMessage::CompositeFieldsMap::iterator it =
+        self->composite_fields->find(field_descriptor);
+    if (it != self->composite_fields->end()) {
+      PyObject* value = it->second;
+      Py_INCREF(value);
+      return value;
+    }
+  }
+
+  const Descriptor* message_descriptor =
+      (reinterpret_cast<CMessageClass*>(Py_TYPE(self)))->message_descriptor;
+  if (self->message->GetDescriptor() != field_descriptor->containing_type()) {
+    PyErr_Format(PyExc_TypeError,
+                 "descriptor to field '%s' doesn't apply to '%s' object",
+                 field_descriptor->full_name().c_str(),
+                 Py_TYPE(self)->tp_name);
+    return NULL;
   }
 
   if (field_descriptor->is_map()) {
@@ -2737,7 +2846,7 @@ PyObject* GetAttr(PyObject* pself, PyObject* name) {
     if (py_container == NULL) {
       return NULL;
     }
-    if (!SetCompositeField(self, name, py_container)) {
+    if (!SetCompositeField(self, field_descriptor, py_container)) {
       Py_DECREF(py_container);
       return NULL;
     }
@@ -2761,7 +2870,7 @@ PyObject* GetAttr(PyObject* pself, PyObject* name) {
     if (py_container == NULL) {
       return NULL;
     }
-    if (!SetCompositeField(self, name, py_container)) {
+    if (!SetCompositeField(self, field_descriptor, py_container)) {
       Py_DECREF(py_container);
       return NULL;
     }
@@ -2773,7 +2882,7 @@ PyObject* GetAttr(PyObject* pself, PyObject* name) {
     if (sub_message == NULL) {
       return NULL;
     }
-    if (!SetCompositeField(self, name, sub_message)) {
+    if (!SetCompositeField(self, field_descriptor, sub_message)) {
       Py_DECREF(sub_message);
       return NULL;
     }
@@ -2783,44 +2892,35 @@ PyObject* GetAttr(PyObject* pself, PyObject* name) {
   return InternalGetScalar(self->message, field_descriptor);
 }
 
-int SetAttr(PyObject* pself, PyObject* name, PyObject* value) {
-  CMessage* self = reinterpret_cast<CMessage*>(pself);
-  if (self->composite_fields && PyDict_Contains(self->composite_fields, name)) {
-    PyErr_SetString(PyExc_TypeError, "Can't set composite field");
+int SetFieldValue(CMessage* self, const FieldDescriptor* field_descriptor,
+                  PyObject* value) {
+  if (self->message->GetDescriptor() != field_descriptor->containing_type()) {
+    PyErr_Format(PyExc_TypeError,
+                 "descriptor to field '%s' doesn't apply to '%s' object",
+                 field_descriptor->full_name().c_str(),
+                 Py_TYPE(self)->tp_name);
     return -1;
-  }
-
-  const FieldDescriptor* field_descriptor = GetFieldDescriptor(self, name);
-  if (field_descriptor != NULL) {
+  } else if (field_descriptor->label() == FieldDescriptor::LABEL_REPEATED) {
+    PyErr_Format(PyExc_AttributeError,
+                 "Assignment not allowed to repeated "
+                 "field \"%s\" in protocol message object.",
+                 field_descriptor->name().c_str());
+    return -1;
+  } else if (field_descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
+    PyErr_Format(PyExc_AttributeError,
+                 "Assignment not allowed to "
+                 "field \"%s\" in protocol message object.",
+                 field_descriptor->name().c_str());
+    return -1;
+  } else {
     AssureWritable(self);
-    if (field_descriptor->label() == FieldDescriptor::LABEL_REPEATED) {
-      PyErr_Format(PyExc_AttributeError, "Assignment not allowed to repeated "
-                   "field \"%s\" in protocol message object.",
-                   field_descriptor->name().c_str());
-      return -1;
-    } else {
-      if (field_descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-        PyErr_Format(PyExc_AttributeError, "Assignment not allowed to "
-                     "field \"%s\" in protocol message object.",
-                     field_descriptor->name().c_str());
-        return -1;
-      } else {
-        return InternalSetScalar(self, field_descriptor, value);
-      }
-    }
+    return InternalSetScalar(self, field_descriptor, value);
   }
-
-  PyErr_Format(PyExc_AttributeError,
-               "Assignment not allowed "
-               "(no field \"%s\" in protocol message object).",
-               PyString_AsString(name));
-  return -1;
 }
-
 }  // namespace cmessage
 
-PyTypeObject CMessage_Type = {
-  PyVarObject_HEAD_INIT(&CMessageClass_Type, 0)
+static CMessageClass _CMessage_Type = { { {
+  PyVarObject_HEAD_INIT(&_CMessageClass_Type, 0)
   FULL_MODULE_NAME ".CMessage",        // tp_name
   sizeof(CMessage),                    // tp_basicsize
   0,                                   //  tp_itemsize
@@ -2837,9 +2937,10 @@ PyTypeObject CMessage_Type = {
   0,                                   //  tp_call
   (reprfunc)cmessage::ToStr,           //  tp_str
   cmessage::GetAttr,                   //  tp_getattro
-  cmessage::SetAttr,                   //  tp_setattro
+  0,                                   //  tp_setattro
   0,                                   //  tp_as_buffer
-  Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  //  tp_flags
+  Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
+      | Py_TPFLAGS_HAVE_VERSION_TAG,   //  tp_flags
   "A ProtocolMessage",                 //  tp_doc
   0,                                   //  tp_traverse
   0,                                   //  tp_clear
@@ -2858,7 +2959,8 @@ PyTypeObject CMessage_Type = {
   (initproc)cmessage::Init,            //  tp_init
   0,                                   //  tp_alloc
   cmessage::New,                       //  tp_new
-};
+} } };
+PyTypeObject* CMessage_Type = &_CMessage_Type.super.ht_type;
 
 // --- Exposing the C proto living inside Python proto to C code:
 
@@ -2884,7 +2986,7 @@ static Message* MutableCProtoInsidePyProtoImpl(PyObject* msg) {
 }
 
 const Message* PyMessage_GetMessagePointer(PyObject* msg) {
-  if (!PyObject_TypeCheck(msg, &CMessage_Type)) {
+  if (!PyObject_TypeCheck(msg, CMessage_Type)) {
     PyErr_SetString(PyExc_TypeError, "Not a Message instance");
     return NULL;
   }
@@ -2893,15 +2995,14 @@ const Message* PyMessage_GetMessagePointer(PyObject* msg) {
 }
 
 Message* PyMessage_GetMutableMessagePointer(PyObject* msg) {
-  if (!PyObject_TypeCheck(msg, &CMessage_Type)) {
+  if (!PyObject_TypeCheck(msg, CMessage_Type)) {
     PyErr_SetString(PyExc_TypeError, "Not a Message instance");
     return NULL;
   }
 
+
   CMessage* cmsg = reinterpret_cast<CMessage*>(msg);
-  if ((cmsg->composite_fields && PyDict_Size(cmsg->composite_fields) != 0) ||
-      (cmsg->extensions != NULL &&
-       PyDict_Size(cmsg->extensions->values) != 0)) {
+  if (cmsg->composite_fields && !cmsg->composite_fields->empty()) {
     // There is currently no way of accurately syncing arbitrary changes to
     // the underlying C++ message back to the CMessage (e.g. removed repeated
     // composite containers). We only allow direct mutation of the underlying
@@ -2945,22 +3046,29 @@ bool InitProto2MessageModule(PyObject *m) {
   // Initialize constants defined in this file.
   InitGlobals();
 
-  CMessageClass_Type.tp_base = &PyType_Type;
-  if (PyType_Ready(&CMessageClass_Type) < 0) {
+  CMessageClass_Type->tp_base = &PyType_Type;
+  if (PyType_Ready(CMessageClass_Type) < 0) {
     return false;
   }
   PyModule_AddObject(m, "MessageMeta",
-                     reinterpret_cast<PyObject*>(&CMessageClass_Type));
+                     reinterpret_cast<PyObject*>(CMessageClass_Type));
 
-  if (PyType_Ready(&CMessage_Type) < 0) {
+  if (PyType_Ready(CMessage_Type) < 0) {
+    return false;
+  }
+  if (PyType_Ready(CFieldProperty_Type) < 0) {
     return false;
   }
 
   // DESCRIPTOR is set on each protocol buffer message class elsewhere, but set
   // it here as well to document that subclasses need to set it.
-  PyDict_SetItem(CMessage_Type.tp_dict, kDESCRIPTOR, Py_None);
+  PyDict_SetItem(CMessage_Type->tp_dict, kDESCRIPTOR, Py_None);
+  // Invalidate any cached data for the CMessage type.
+  // This call is necessary to correctly support Py_TPFLAGS_HAVE_VERSION_TAG,
+  // after we have modified CMessage_Type.tp_dict.
+  PyType_Modified(CMessage_Type);
 
-  PyModule_AddObject(m, "Message", reinterpret_cast<PyObject*>(&CMessage_Type));
+  PyModule_AddObject(m, "Message", reinterpret_cast<PyObject*>(CMessage_Type));
 
   // Initialize Repeated container types.
   {
@@ -3003,6 +3111,22 @@ bool InitProto2MessageModule(PyObject *m) {
     }
   }
 
+  if (PyType_Ready(&PyUnknownFields_Type) < 0) {
+    return false;
+  }
+
+  PyModule_AddObject(m, "UnknownFieldSet",
+                     reinterpret_cast<PyObject*>(
+                         &PyUnknownFields_Type));
+
+  if (PyType_Ready(&PyUnknownFieldRef_Type) < 0) {
+    return false;
+  }
+
+  PyModule_AddObject(m, "UnknownField",
+                     reinterpret_cast<PyObject*>(
+                         &PyUnknownFieldRef_Type));
+
   // Initialize Map container types.
   if (!InitMapContainers()) {
     return false;
diff --git a/python/google/protobuf/pyext/message.h b/python/google/protobuf/pyext/message.h
index d754e62a..e729e448 100644
--- a/python/google/protobuf/pyext/message.h
+++ b/python/google/protobuf/pyext/message.h
@@ -38,6 +38,7 @@
 
 #include <memory>
 #include <string>
+#include <hash_map>
 
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/pyext/thread_unsafe_shared_ptr.h>
@@ -96,26 +97,25 @@ typedef struct CMessage {
   // made writable, at which point this field is set to false.
   bool read_only;
 
-  // A reference to a Python dictionary containing CMessage,
+  // A mapping indexed by field, containing CMessage,
   // RepeatedCompositeContainer, and RepeatedScalarContainer
   // objects. Used as a cache to make sure we don't have to make a
   // Python wrapper for the C++ Message objects on every access, or
   // deal with the synchronization nightmare that could create.
-  PyObject* composite_fields;
+  // Also cache extension fields.
+  // The FieldDescriptor is owned by the message's pool; PyObject references
+  // are owned.
+  typedef __gnu_cxx::hash_map<const FieldDescriptor*, PyObject*>
+      CompositeFieldsMap;
+  CompositeFieldsMap* composite_fields;
 
-  // A reference to the dictionary containing the message's extensions.
-  // Similar to composite_fields, acting as a cache, but also contains the
-  // required extension dict logic.
-  ExtensionDict* extensions;
+  // A reference to PyUnknownFields.
+  PyObject* unknown_field_set;
 
   // Implements the "weakref" protocol for this object.
   PyObject* weakreflist;
 } CMessage;
 
-extern PyTypeObject CMessageClass_Type;
-extern PyTypeObject CMessage_Type;
-
-
 // The (meta) type of all Messages classes.
 // It allows us to cache some C++ pointers in the class object itself, they are
 // faster to extract than from the type's dictionary.
@@ -142,6 +142,8 @@ struct CMessageClass {
   }
 };
 
+extern PyTypeObject* CMessageClass_Type;
+extern PyTypeObject* CMessage_Type;
 
 namespace cmessage {
 
@@ -235,15 +237,13 @@ PyObject* MergeFrom(CMessage* self, PyObject* arg);
 // has been registered with the same field number on this class.
 PyObject* RegisterExtension(PyObject* cls, PyObject* extension_handle);
 
-// Retrieves an attribute named 'name' from 'self', which is interpreted as a
-// CMessage. Returns the attribute value on success, or null on failure.
-//
-// Returns a new reference.
-PyObject* GetAttr(PyObject* self, PyObject* name);
-
-// Set the value of the attribute named 'name', for 'self', which is interpreted
-// as a CMessage, to the value 'value'. Returns -1 on failure.
-int SetAttr(PyObject* self, PyObject* name, PyObject* value);
+// Get a field from a message.
+PyObject* GetFieldValue(CMessage* self,
+                        const FieldDescriptor* field_descriptor);
+// Sets the value of a scalar field in a message.
+// On error, return -1 with an extension set.
+int SetFieldValue(CMessage* self, const FieldDescriptor* field_descriptor,
+                  PyObject* value);
 
 PyObject* FindInitializationErrors(CMessage* self);
 
@@ -357,6 +357,6 @@ extern template bool CheckAndGetInteger<uint64>(PyObject*, uint64*);
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_MESSAGE_H__
diff --git a/python/google/protobuf/pyext/message_factory.cc b/python/google/protobuf/pyext/message_factory.cc
index bacc76a6..efaa2617 100644
--- a/python/google/protobuf/pyext/message_factory.cc
+++ b/python/google/protobuf/pyext/message_factory.cc
@@ -28,6 +28,8 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+#include <unordered_map>
+
 #include <Python.h>
 
 #include <google/protobuf/dynamic_message.h>
@@ -137,7 +139,7 @@ CMessageClass* GetOrCreateMessageClass(PyMessageFactory* self,
   // This is the same implementation as MessageFactory.GetPrototype().
 
   // Do not create a MessageClass that already exists.
-  hash_map<const Descriptor*, CMessageClass*>::iterator it =
+  std::unordered_map<const Descriptor*, CMessageClass*>::iterator it =
       self->classes_by_descriptor->find(descriptor);
   if (it != self->classes_by_descriptor->end()) {
     Py_INCREF(it->second);
@@ -158,7 +160,7 @@ CMessageClass* GetOrCreateMessageClass(PyMessageFactory* self,
     return NULL;
   }
   ScopedPyObjectPtr message_class(PyObject_CallObject(
-      reinterpret_cast<PyObject*>(&CMessageClass_Type), args.get()));
+      reinterpret_cast<PyObject*>(CMessageClass_Type), args.get()));
   if (message_class == NULL) {
     return NULL;
   }
diff --git a/python/google/protobuf/pyext/message_factory.h b/python/google/protobuf/pyext/message_factory.h
index 36092f7e..06444b0a 100644
--- a/python/google/protobuf/pyext/message_factory.h
+++ b/python/google/protobuf/pyext/message_factory.h
@@ -33,7 +33,7 @@
 
 #include <Python.h>
 
-#include <google/protobuf/stubs/hash.h>
+#include <unordered_map>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/pyext/descriptor_pool.h>
 
@@ -66,7 +66,8 @@ struct PyMessageFactory {
   //
   // Descriptor pointers stored here are owned by the DescriptorPool above.
   // Python references to classes are owned by this PyDescriptorPool.
-  typedef hash_map<const Descriptor*, CMessageClass*> ClassesByMessageMap;
+  typedef std::unordered_map<const Descriptor*, CMessageClass*>
+      ClassesByMessageMap;
   ClassesByMessageMap* classes_by_descriptor;
 };
 
@@ -98,6 +99,6 @@ bool InitMessageFactory();
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_MESSAGE_FACTORY_H__
diff --git a/python/google/protobuf/pyext/message_module.cc b/python/google/protobuf/pyext/message_module.cc
index 8c933866..29d56702 100644
--- a/python/google/protobuf/pyext/message_module.cc
+++ b/python/google/protobuf/pyext/message_module.cc
@@ -31,47 +31,24 @@
 #include <Python.h>
 
 #include <google/protobuf/pyext/message.h>
-#include <google/protobuf/proto_api.h>
+#include <google/protobuf/python/proto_api.h>
 
 #include <google/protobuf/message_lite.h>
 
 namespace {
 
 // C++ API.  Clients get at this via proto_api.h
-struct ApiImplementation : google::protobuf::python::PyProto_API {
-  const google::protobuf::Message*
-      GetMessagePointer(PyObject* msg) const override {
-    return google::protobuf::python::PyMessage_GetMessagePointer(msg);
+struct ApiImplementation : proto2::python::PyProto_API {
+  const proto2::Message* GetMessagePointer(PyObject* msg) const override {
+    return proto2::python::PyMessage_GetMessagePointer(msg);
   }
-  google::protobuf::Message*
-      GetMutableMessagePointer(PyObject* msg) const override {
-    return google::protobuf::python::PyMessage_GetMutableMessagePointer(msg);
+  proto2::Message* GetMutableMessagePointer(PyObject* msg) const override {
+    return proto2::python::PyMessage_GetMutableMessagePointer(msg);
   }
 };
 
 }  // namespace
 
-static PyObject* GetPythonProto3PreserveUnknownsDefault(
-    PyObject* /*m*/, PyObject* /*args*/) {
-  if (google::protobuf::internal::GetProto3PreserveUnknownsDefault()) {
-    Py_RETURN_TRUE;
-  } else {
-    Py_RETURN_FALSE;
-  }
-}
-
-static PyObject* SetPythonProto3PreserveUnknownsDefault(
-    PyObject* /*m*/, PyObject* arg) {
-  if (!arg || !PyBool_Check(arg)) {
-    PyErr_SetString(
-        PyExc_TypeError,
-        "Argument to SetPythonProto3PreserveUnknownsDefault must be boolean");
-    return NULL;
-  }
-  google::protobuf::internal::SetProto3PreserveUnknownsDefault(PyObject_IsTrue(arg));
-  Py_RETURN_NONE;
-}
-
 static const char module_docstring[] =
 "python-proto2 is a module that can be used to enhance proto2 Python API\n"
 "performance.\n"
@@ -81,16 +58,9 @@ static const char module_docstring[] =
 
 static PyMethodDef ModuleMethods[] = {
   {"SetAllowOversizeProtos",
-    (PyCFunction)google::protobuf::python::cmessage::SetAllowOversizeProtos,
+    (PyCFunction)proto2::python::cmessage::SetAllowOversizeProtos,
     METH_O, "Enable/disable oversize proto parsing."},
   // DO NOT USE: For migration and testing only.
-  {"GetPythonProto3PreserveUnknownsDefault",
-    (PyCFunction)GetPythonProto3PreserveUnknownsDefault,
-    METH_NOARGS, "Get Proto3 preserve unknowns default."},
-  // DO NOT USE: For migration and testing only.
-  {"SetPythonProto3PreserveUnknownsDefault",
-    (PyCFunction)SetPythonProto3PreserveUnknownsDefault,
-    METH_O, "Enable/disable proto3 unknowns preservation."},
   { NULL, NULL}
 };
 
@@ -113,35 +83,32 @@ static struct PyModuleDef _module = {
 #define INITFUNC_ERRORVAL
 #endif
 
-extern "C" {
-  PyMODINIT_FUNC INITFUNC(void) {
-    PyObject* m;
+PyMODINIT_FUNC INITFUNC() {
+  PyObject* m;
 #if PY_MAJOR_VERSION >= 3
-    m = PyModule_Create(&_module);
+  m = PyModule_Create(&_module);
 #else
-    m = Py_InitModule3("_message", ModuleMethods,
-                       module_docstring);
+  m = Py_InitModule3("_message", ModuleMethods, module_docstring);
 #endif
-    if (m == NULL) {
-      return INITFUNC_ERRORVAL;
-    }
+  if (m == NULL) {
+    return INITFUNC_ERRORVAL;
+  }
 
-    if (!google::protobuf::python::InitProto2MessageModule(m)) {
-      Py_DECREF(m);
-      return INITFUNC_ERRORVAL;
-    }
-    
-    // Adds the C++ API
-    if (PyObject* api =
-            PyCapsule_New(new ApiImplementation(),
-                          google::protobuf::python::PyProtoAPICapsuleName(), NULL)) {
-      PyModule_AddObject(m, "proto_API", api);
-    } else {
-      return INITFUNC_ERRORVAL;
-    }
+  if (!proto2::python::InitProto2MessageModule(m)) {
+    Py_DECREF(m);
+    return INITFUNC_ERRORVAL;
+  }
+
+  // Adds the C++ API
+  if (PyObject* api =
+          PyCapsule_New(new ApiImplementation(),
+                        proto2::python::PyProtoAPICapsuleName(), NULL)) {
+    PyModule_AddObject(m, "proto_API", api);
+  } else {
+    return INITFUNC_ERRORVAL;
+  }
 
 #if PY_MAJOR_VERSION >= 3
-    return m;
+  return m;
 #endif
-  }
 }
diff --git a/python/google/protobuf/pyext/repeated_composite_container.cc b/python/google/protobuf/pyext/repeated_composite_container.cc
index 5874d5de..d6bc3d7b 100644
--- a/python/google/protobuf/pyext/repeated_composite_container.cc
+++ b/python/google/protobuf/pyext/repeated_composite_container.cc
@@ -61,9 +61,9 @@ namespace repeated_composite_container {
 
 // TODO(tibell): We might also want to check:
 //   GOOGLE_CHECK_NOTNULL((self)->owner.get());
-#define GOOGLE_CHECK_ATTACHED(self)             \
-  do {                                   \
-    GOOGLE_CHECK_NOTNULL((self)->message);      \
+#define GOOGLE_CHECK_ATTACHED(self)                           \
+  do {                                                 \
+    GOOGLE_CHECK_NOTNULL((self)->message);                 \
     GOOGLE_CHECK_NOTNULL((self)->parent_field_descriptor); \
   } while (0);
 
@@ -152,6 +152,8 @@ static PyObject* AddToAttached(RepeatedCompositeContainer* self,
   cmsg->message = sub_message;
   cmsg->parent = self->parent;
   if (cmessage::InitAttributes(cmsg, args, kwargs) < 0) {
+    message->GetReflection()->RemoveLast(
+        message, self->parent_field_descriptor);
     Py_DECREF(cmsg);
     return NULL;
   }
@@ -210,7 +212,7 @@ PyObject* Extend(RepeatedCompositeContainer* self, PyObject* value) {
   }
   ScopedPyObjectPtr next;
   while ((next.reset(PyIter_Next(iter.get()))) != NULL) {
-    if (!PyObject_TypeCheck(next.get(), &CMessage_Type)) {
+    if (!PyObject_TypeCheck(next.get(), CMessage_Type)) {
       PyErr_SetString(PyExc_TypeError, "Not a cmessage");
       return NULL;
     }
@@ -487,9 +489,9 @@ static PyObject* Pop(PyObject* pself, PyObject* args) {
 void ReleaseLastTo(CMessage* parent,
                    const FieldDescriptor* field,
                    CMessage* target) {
-  GOOGLE_CHECK_NOTNULL(parent);
-  GOOGLE_CHECK_NOTNULL(field);
-  GOOGLE_CHECK_NOTNULL(target);
+  GOOGLE_CHECK(parent != nullptr);
+  GOOGLE_CHECK(field != nullptr);
+  GOOGLE_CHECK(target != nullptr);
 
   CMessage::OwnerRef released_message(
       parent->message->GetReflection()->ReleaseLast(parent->message, field));
diff --git a/python/google/protobuf/pyext/repeated_composite_container.h b/python/google/protobuf/pyext/repeated_composite_container.h
index e5e946aa..464699aa 100644
--- a/python/google/protobuf/pyext/repeated_composite_container.h
+++ b/python/google/protobuf/pyext/repeated_composite_container.h
@@ -161,6 +161,6 @@ void ReleaseLastTo(CMessage* parent,
 }  // namespace repeated_composite_container
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_REPEATED_COMPOSITE_CONTAINER_H__
diff --git a/python/google/protobuf/pyext/repeated_scalar_container.cc b/python/google/protobuf/pyext/repeated_scalar_container.cc
index de3b6e14..cdb64269 100644
--- a/python/google/protobuf/pyext/repeated_scalar_container.cc
+++ b/python/google/protobuf/pyext/repeated_scalar_container.cc
@@ -663,6 +663,10 @@ static PyObject* ToStr(PyObject* pself) {
   return PyObject_Repr(list.get());
 }
 
+static PyObject* MergeFrom(PyObject* pself, PyObject* arg) {
+  return Extend(reinterpret_cast<RepeatedScalarContainer*>(pself), arg);
+}
+
 // The private constructor of RepeatedScalarContainer objects.
 PyObject *NewContainer(
     CMessage* parent, const FieldDescriptor* parent_field_descriptor) {
@@ -776,6 +780,8 @@ static PyMethodDef Methods[] = {
     "Removes an object from the repeated container." },
   { "sort", (PyCFunction)Sort, METH_VARARGS | METH_KEYWORDS,
     "Sorts the repeated container."},
+  { "MergeFrom", (PyCFunction)MergeFrom, METH_O,
+    "Merges a repeated container into the current container." },
   { NULL, NULL }
 };
 
diff --git a/python/google/protobuf/pyext/repeated_scalar_container.h b/python/google/protobuf/pyext/repeated_scalar_container.h
index 559dec98..4dcecbac 100644
--- a/python/google/protobuf/pyext/repeated_scalar_container.h
+++ b/python/google/protobuf/pyext/repeated_scalar_container.h
@@ -104,6 +104,6 @@ void SetOwner(RepeatedScalarContainer* self,
 }  // namespace repeated_scalar_container
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_REPEATED_SCALAR_CONTAINER_H__
diff --git a/python/google/protobuf/pyext/safe_numerics.h b/python/google/protobuf/pyext/safe_numerics.h
index 639ba2c8..60112cfa 100644
--- a/python/google/protobuf/pyext/safe_numerics.h
+++ b/python/google/protobuf/pyext/safe_numerics.h
@@ -159,6 +159,6 @@ inline Dest checked_numeric_cast(Source source) {
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_SAFE_NUMERICS_H__
diff --git a/python/google/protobuf/pyext/thread_unsafe_shared_ptr.h b/python/google/protobuf/pyext/thread_unsafe_shared_ptr.h
index ad804b5f..79fa9e3d 100644
--- a/python/google/protobuf/pyext/thread_unsafe_shared_ptr.h
+++ b/python/google/protobuf/pyext/thread_unsafe_shared_ptr.h
@@ -99,6 +99,6 @@ class ThreadUnsafeSharedPtr {
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_CPP_THREAD_UNSAFE_SHARED_PTR_H__
diff --git a/python/google/protobuf/python_protobuf.h b/python/google/protobuf/python_protobuf.h
index beb6e460..8db1ffb7 100644
--- a/python/google/protobuf/python_protobuf.h
+++ b/python/google/protobuf/python_protobuf.h
@@ -52,6 +52,6 @@ Message* MutableCProtoInsidePyProto(PyObject* msg);
 
 }  // namespace python
 }  // namespace protobuf
-
 }  // namespace google
+
 #endif  // GOOGLE_PROTOBUF_PYTHON_PYTHON_PROTOBUF_H__
diff --git a/python/google/protobuf/reflection.py b/python/google/protobuf/reflection.py
index f4ce8caf..81e18859 100755
--- a/python/google/protobuf/reflection.py
+++ b/python/google/protobuf/reflection.py
@@ -48,25 +48,23 @@ this file*.
 __author__ = 'robinson@google.com (Will Robinson)'
 
 
-from google.protobuf.internal import api_implementation
-from google.protobuf import message
-
-
-if api_implementation.Type() == 'cpp':
-  from google.protobuf.pyext import cpp_message as message_impl
-else:
-  from google.protobuf.internal import python_message as message_impl
+from google.protobuf import message_factory
+from google.protobuf import symbol_database
 
 # The type of all Message classes.
 # Part of the public interface, but normally only used by message factories.
-GeneratedProtocolMessageType = message_impl.GeneratedProtocolMessageType
+GeneratedProtocolMessageType = message_factory._GENERATED_PROTOCOL_MESSAGE_TYPE
 
 MESSAGE_CLASS_CACHE = {}
 
 
+# Deprecated. Please NEVER use reflection.ParseMessage().
 def ParseMessage(descriptor, byte_str):
   """Generate a new Message instance from this Descriptor and a byte string.
 
+  DEPRECATED: ParseMessage is deprecated because it is using MakeClass().
+  Please use MessageFactory.GetPrototype() instead.
+
   Args:
     descriptor: Protobuf Descriptor object
     byte_str: Serialized protocol buffer byte string
@@ -80,42 +78,18 @@ def ParseMessage(descriptor, byte_str):
   return new_msg
 
 
+# Deprecated. Please NEVER use reflection.MakeClass().
 def MakeClass(descriptor):
   """Construct a class object for a protobuf described by descriptor.
 
-  Composite descriptors are handled by defining the new class as a member of the
-  parent class, recursing as deep as necessary.
-  This is the dynamic equivalent to:
-
-  class Parent(message.Message):
-    __metaclass__ = GeneratedProtocolMessageType
-    DESCRIPTOR = descriptor
-    class Child(message.Message):
-      __metaclass__ = GeneratedProtocolMessageType
-      DESCRIPTOR = descriptor.nested_types[0]
-
-  Sample usage:
-    file_descriptor = descriptor_pb2.FileDescriptorProto()
-    file_descriptor.ParseFromString(proto2_string)
-    msg_descriptor = descriptor.MakeDescriptor(file_descriptor.message_type[0])
-    msg_class = reflection.MakeClass(msg_descriptor)
-    msg = msg_class()
+  DEPRECATED: use MessageFactory.GetPrototype() instead.
 
   Args:
     descriptor: A descriptor.Descriptor object describing the protobuf.
   Returns:
     The Message class object described by the descriptor.
   """
-  if descriptor in MESSAGE_CLASS_CACHE:
-    return MESSAGE_CLASS_CACHE[descriptor]
-
-  attributes = {}
-  for name, nested_type in descriptor.nested_types_by_name.items():
-    attributes[name] = MakeClass(nested_type)
-
-  attributes[GeneratedProtocolMessageType._DESCRIPTOR_KEY] = descriptor
-
-  result = GeneratedProtocolMessageType(
-      str(descriptor.name), (message.Message,), attributes)
-  MESSAGE_CLASS_CACHE[descriptor] = result
-  return result
+  # Original implementation leads to duplicate message classes, which won't play
+  # well with extensions. Message factory info is also missing.
+  # Redirect to message_factory.
+  return symbol_database.Default().GetPrototype(descriptor)
diff --git a/python/google/protobuf/text_encoding.py b/python/google/protobuf/text_encoding.py
index 98995638..39898765 100644
--- a/python/google/protobuf/text_encoding.py
+++ b/python/google/protobuf/text_encoding.py
@@ -33,59 +33,70 @@ import re
 
 import six
 
-# Lookup table for utf8
-_cescape_utf8_to_str = [chr(i) for i in range(0, 256)]
-_cescape_utf8_to_str[9] = r'\t'  # optional escape
-_cescape_utf8_to_str[10] = r'\n'  # optional escape
-_cescape_utf8_to_str[13] = r'\r'  # optional escape
-_cescape_utf8_to_str[39] = r"\'"  # optional escape
-
-_cescape_utf8_to_str[34] = r'\"'  # necessary escape
-_cescape_utf8_to_str[92] = r'\\'  # necessary escape
+_cescape_chr_to_symbol_map = {}
+_cescape_chr_to_symbol_map[9] = r'\t'  # optional escape
+_cescape_chr_to_symbol_map[10] = r'\n'  # optional escape
+_cescape_chr_to_symbol_map[13] = r'\r'  # optional escape
+_cescape_chr_to_symbol_map[34] = r'\"'  # necessary escape
+_cescape_chr_to_symbol_map[39] = r"\'"  # optional escape
+_cescape_chr_to_symbol_map[92] = r'\\'  # necessary escape
+
+# Lookup table for unicode
+_cescape_unicode_to_str = [chr(i) for i in range(0, 256)]
+for byte, string in _cescape_chr_to_symbol_map.items():
+  _cescape_unicode_to_str[byte] = string
 
 # Lookup table for non-utf8, with necessary escapes at (o >= 127 or o < 32)
 _cescape_byte_to_str = ([r'\%03o' % i for i in range(0, 32)] +
                         [chr(i) for i in range(32, 127)] +
                         [r'\%03o' % i for i in range(127, 256)])
-_cescape_byte_to_str[9] = r'\t'  # optional escape
-_cescape_byte_to_str[10] = r'\n'  # optional escape
-_cescape_byte_to_str[13] = r'\r'  # optional escape
-_cescape_byte_to_str[39] = r"\'"  # optional escape
-
-_cescape_byte_to_str[34] = r'\"'  # necessary escape
-_cescape_byte_to_str[92] = r'\\'  # necessary escape
+for byte, string in _cescape_chr_to_symbol_map.items():
+  _cescape_byte_to_str[byte] = string
+del byte, string
 
 
 def CEscape(text, as_utf8):
-  """Escape a bytes string for use in an ascii protocol buffer.
-
-  text.encode('string_escape') does not seem to satisfy our needs as it
-  encodes unprintable characters using two-digit hex escapes whereas our
-  C++ unescaping function allows hex escapes to be any length.  So,
-  "\0011".encode('string_escape') ends up being "\\x011", which will be
-  decoded in C++ as a single-character string with char code 0x11.
+  # type: (...) -> str
+  """Escape a bytes string for use in an text protocol buffer.
 
   Args:
-    text: A byte string to be escaped
-    as_utf8: Specifies if result should be returned in UTF-8 encoding
+    text: A byte string to be escaped.
+    as_utf8: Specifies if result may contain non-ASCII characters.
+        In Python 3 this allows unescaped non-ASCII Unicode characters.
+        In Python 2 the return value will be valid UTF-8 rather than only ASCII.
   Returns:
-    Escaped string
+    Escaped string (str).
   """
-  # PY3 hack: make Ord work for str and bytes:
-  # //platforms/networking/data uses unicode here, hence basestring.
-  Ord = ord if isinstance(text, six.string_types) else lambda x: x
+  # Python's text.encode() 'string_escape' or 'unicode_escape' codecs do not
+  # satisfy our needs; they encodes unprintable characters using two-digit hex
+  # escapes whereas our C++ unescaping function allows hex escapes to be any
+  # length.  So, "\0011".encode('string_escape') ends up being "\\x011", which
+  # will be decoded in C++ as a single-character string with char code 0x11.
+  if six.PY3:
+    text_is_unicode = isinstance(text, str)
+    if as_utf8 and text_is_unicode:
+      # We're already unicode, no processing beyond control char escapes.
+      return text.translate(_cescape_chr_to_symbol_map)
+    ord_ = ord if text_is_unicode else lambda x: x  # bytes iterate as ints.
+  else:
+    ord_ = ord  # PY2
   if as_utf8:
-    return ''.join(_cescape_utf8_to_str[Ord(c)] for c in text)
-  return ''.join(_cescape_byte_to_str[Ord(c)] for c in text)
+    return ''.join(_cescape_unicode_to_str[ord_(c)] for c in text)
+  return ''.join(_cescape_byte_to_str[ord_(c)] for c in text)
 
 
 _CUNESCAPE_HEX = re.compile(r'(\\+)x([0-9a-fA-F])(?![0-9a-fA-F])')
-_cescape_highbit_to_str = ([chr(i) for i in range(0, 127)] +
-                           [r'\%03o' % i for i in range(127, 256)])
 
 
 def CUnescape(text):
-  """Unescape a text string with C-style escape sequences to UTF-8 bytes."""
+  # type: (str) -> bytes
+  """Unescape a text string with C-style escape sequences to UTF-8 bytes.
+
+  Args:
+    text: The data to parse in a str.
+  Returns:
+    A byte string.
+  """
 
   def ReplaceHex(m):
     # Only replace the match if the number of leading back slashes is odd. i.e.
@@ -98,10 +109,9 @@ def CUnescape(text):
   # allow single-digit hex escapes (like '\xf').
   result = _CUNESCAPE_HEX.sub(ReplaceHex, text)
 
-  if str is bytes:  # PY2
+  if six.PY2:
     return result.decode('string_escape')
-  result = ''.join(_cescape_highbit_to_str[ord(c)] for c in result)
-  return (result.encode('ascii')  # Make it bytes to allow decode.
+  return (result.encode('utf-8')  # PY3: Make it bytes to allow decode.
           .decode('unicode_escape')
           # Make it bytes again to return the proper type.
           .encode('raw_unicode_escape'))
diff --git a/python/google/protobuf/text_format.py b/python/google/protobuf/text_format.py
index 2cbd21bc..5dd41830 100755
--- a/python/google/protobuf/text_format.py
+++ b/python/google/protobuf/text_format.py
@@ -55,15 +55,15 @@ from google.protobuf.internal import type_checkers
 from google.protobuf import descriptor
 from google.protobuf import text_encoding
 
-__all__ = ['MessageToString', 'PrintMessage', 'PrintField', 'PrintFieldValue',
-           'Merge']
+__all__ = ['MessageToString', 'Parse', 'PrintMessage', 'PrintField',
+           'PrintFieldValue', 'Merge', 'MessageToBytes']
 
 _INTEGER_CHECKERS = (type_checkers.Uint32ValueChecker(),
                      type_checkers.Int32ValueChecker(),
                      type_checkers.Uint64ValueChecker(),
                      type_checkers.Int64ValueChecker())
-_FLOAT_INFINITY = re.compile('-?inf(?:inity)?f?', re.IGNORECASE)
-_FLOAT_NAN = re.compile('nanf?', re.IGNORECASE)
+_FLOAT_INFINITY = re.compile('-?inf(?:inity)?f?$', re.IGNORECASE)
+_FLOAT_NAN = re.compile('nanf?$', re.IGNORECASE)
 _FLOAT_TYPES = frozenset([descriptor.FieldDescriptor.CPPTYPE_FLOAT,
                           descriptor.FieldDescriptor.CPPTYPE_DOUBLE])
 _QUOTES = frozenset(("'", '"'))
@@ -121,6 +121,7 @@ class TextWriter(object):
 def MessageToString(message,
                     as_utf8=False,
                     as_one_line=False,
+                    use_short_repeated_primitives=False,
                     pointy_brackets=False,
                     use_index_order=False,
                     float_format=None,
@@ -128,6 +129,7 @@ def MessageToString(message,
                     descriptor_pool=None,
                     indent=0,
                     message_formatter=None):
+  # type: (...) -> str
   """Convert protobuf message to text format.
 
   Floating point values can be formatted compactly with 15 digits of
@@ -137,8 +139,11 @@ def MessageToString(message,
 
   Args:
     message: The protocol buffers message.
-    as_utf8: Produce text output in UTF8 format.
+    as_utf8: Return unescaped Unicode for non-ASCII characters.
+        In Python 3 actual Unicode characters may appear as is in strings.
+        In Python 2 the return value will be valid UTF-8 rather than only ASCII.
     as_one_line: Don't introduce newlines between fields.
+    use_short_repeated_primitives: Use short repeated format for primitives.
     pointy_brackets: If True, use angle brackets instead of curly braces for
       nesting.
     use_index_order: If True, fields of a proto message will be printed using
@@ -159,7 +164,8 @@ def MessageToString(message,
     A string of the text formatted protocol buffer message.
   """
   out = TextWriter(as_utf8)
-  printer = _Printer(out, indent, as_utf8, as_one_line, pointy_brackets,
+  printer = _Printer(out, indent, as_utf8, as_one_line,
+                     use_short_repeated_primitives, pointy_brackets,
                      use_index_order, float_format, use_field_number,
                      descriptor_pool, message_formatter)
   printer.PrintMessage(message)
@@ -170,6 +176,16 @@ def MessageToString(message,
   return result
 
 
+def MessageToBytes(message, **kwargs):
+  # type: (...) -> bytes
+  """Convert protobuf message to encoded text format.  See MessageToString."""
+  text = MessageToString(message, **kwargs)
+  if isinstance(text, bytes):
+    return text
+  codec = 'utf-8' if kwargs.get('as_utf8') else 'ascii'
+  return text.encode(codec)
+
+
 def _IsMapEntry(field):
   return (field.type == descriptor.FieldDescriptor.TYPE_MESSAGE and
           field.message_type.has_options and
@@ -181,13 +197,15 @@ def PrintMessage(message,
                  indent=0,
                  as_utf8=False,
                  as_one_line=False,
+                 use_short_repeated_primitives=False,
                  pointy_brackets=False,
                  use_index_order=False,
                  float_format=None,
                  use_field_number=False,
                  descriptor_pool=None,
                  message_formatter=None):
-  printer = _Printer(out, indent, as_utf8, as_one_line, pointy_brackets,
+  printer = _Printer(out, indent, as_utf8, as_one_line,
+                     use_short_repeated_primitives, pointy_brackets,
                      use_index_order, float_format, use_field_number,
                      descriptor_pool, message_formatter)
   printer.PrintMessage(message)
@@ -199,12 +217,14 @@ def PrintField(field,
                indent=0,
                as_utf8=False,
                as_one_line=False,
+               use_short_repeated_primitives=False,
                pointy_brackets=False,
                use_index_order=False,
                float_format=None,
                message_formatter=None):
   """Print a single field name/value pair."""
-  printer = _Printer(out, indent, as_utf8, as_one_line, pointy_brackets,
+  printer = _Printer(out, indent, as_utf8, as_one_line,
+                     use_short_repeated_primitives, pointy_brackets,
                      use_index_order, float_format, message_formatter)
   printer.PrintField(field, value)
 
@@ -215,12 +235,14 @@ def PrintFieldValue(field,
                     indent=0,
                     as_utf8=False,
                     as_one_line=False,
+                    use_short_repeated_primitives=False,
                     pointy_brackets=False,
                     use_index_order=False,
                     float_format=None,
                     message_formatter=None):
   """Print a single field value (not including name)."""
-  printer = _Printer(out, indent, as_utf8, as_one_line, pointy_brackets,
+  printer = _Printer(out, indent, as_utf8, as_one_line,
+                     use_short_repeated_primitives, pointy_brackets,
                      use_index_order, float_format, message_formatter)
   printer.PrintFieldValue(field, value)
 
@@ -258,6 +280,7 @@ class _Printer(object):
                indent=0,
                as_utf8=False,
                as_one_line=False,
+               use_short_repeated_primitives=False,
                pointy_brackets=False,
                use_index_order=False,
                float_format=None,
@@ -274,8 +297,11 @@ class _Printer(object):
     Args:
       out: To record the text format result.
       indent: The indent level for pretty print.
-      as_utf8: Produce text output in UTF8 format.
+      as_utf8: Return unescaped Unicode for non-ASCII characters.
+          In Python 3 actual Unicode characters may appear as is in strings.
+          In Python 2 the return value will be valid UTF-8 rather than ASCII.
       as_one_line: Don't introduce newlines between fields.
+      use_short_repeated_primitives: Use short repeated format for primitives.
       pointy_brackets: If True, use angle brackets instead of curly braces for
         nesting.
       use_index_order: If True, print fields of a proto message using the order
@@ -294,6 +320,7 @@ class _Printer(object):
     self.indent = indent
     self.as_utf8 = as_utf8
     self.as_one_line = as_one_line
+    self.use_short_repeated_primitives = use_short_repeated_primitives
     self.pointy_brackets = pointy_brackets
     self.use_index_order = use_index_order
     self.float_format = float_format
@@ -351,13 +378,18 @@ class _Printer(object):
           entry_submsg = value.GetEntryClass()(key=key, value=value[key])
           self.PrintField(field, entry_submsg)
       elif field.label == descriptor.FieldDescriptor.LABEL_REPEATED:
-        for element in value:
-          self.PrintField(field, element)
+        if (self.use_short_repeated_primitives
+            and field.cpp_type != descriptor.FieldDescriptor.CPPTYPE_MESSAGE
+            and field.cpp_type != descriptor.FieldDescriptor.CPPTYPE_STRING):
+          self._PrintShortRepeatedPrimitivesValue(field, value)
+        else:
+          for element in value:
+            self.PrintField(field, element)
       else:
         self.PrintField(field, value)
 
-  def PrintField(self, field, value):
-    """Print a single field name/value pair."""
+  def _PrintFieldName(self, field):
+    """Print field name."""
     out = self.out
     out.write(' ' * self.indent)
     if self.use_field_number:
@@ -383,11 +415,22 @@ class _Printer(object):
       # don't include it.
       out.write(': ')
 
+  def PrintField(self, field, value):
+    """Print a single field name/value pair."""
+    self._PrintFieldName(field)
     self.PrintFieldValue(field, value)
-    if self.as_one_line:
-      out.write(' ')
-    else:
-      out.write('\n')
+    self.out.write(' ' if self.as_one_line else '\n')
+
+  def _PrintShortRepeatedPrimitivesValue(self, field, value):
+    # Note: this is called only when value has at least one element.
+    self._PrintFieldName(field)
+    self.out.write('[')
+    for i in xrange(len(value) - 1):
+      self.PrintFieldValue(field, value[i])
+      self.out.write(', ')
+    self.PrintFieldValue(field, value[-1])
+    self.out.write(']')
+    self.out.write(' ' if self.as_one_line else '\n')
 
   def _PrintMessageFieldValue(self, value):
     if self.pointy_brackets:
@@ -428,12 +471,12 @@ class _Printer(object):
         out.write(str(value))
     elif field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_STRING:
       out.write('\"')
-      if isinstance(value, six.text_type):
+      if isinstance(value, six.text_type) and (six.PY2 or not self.as_utf8):
         out_value = value.encode('utf-8')
       else:
         out_value = value
       if field.type == descriptor.FieldDescriptor.TYPE_BYTES:
-        # We need to escape non-UTF8 chars in TYPE_BYTES field.
+        # We always need to escape all binary data in TYPE_BYTES fields.
         out_as_utf8 = False
       else:
         out_as_utf8 = self.as_utf8
@@ -487,12 +530,7 @@ def Parse(text,
   Raises:
     ParseError: On text parsing problems.
   """
-  if not isinstance(text, str):
-    if six.PY3:
-      text = text.decode('utf-8')
-    else:
-      text = text.encode('utf-8')
-  return ParseLines(text.split('\n'),
+  return ParseLines(text.split(b'\n' if isinstance(text, bytes) else u'\n'),
                     message,
                     allow_unknown_extension,
                     allow_field_number,
@@ -523,13 +561,8 @@ def Merge(text,
   Raises:
     ParseError: On text parsing problems.
   """
-  if not isinstance(text, str):
-    if six.PY3:
-      text = text.decode('utf-8')
-    else:
-      text = text.encode('utf-8')
   return MergeLines(
-      text.split('\n'),
+      text.split(b'\n' if isinstance(text, bytes) else u'\n'),
       message,
       allow_unknown_extension,
       allow_field_number,
@@ -570,6 +603,9 @@ def MergeLines(lines,
                descriptor_pool=None):
   """Parses a text representation of a protocol message into a message.
 
+  Like ParseLines(), but allows repeated values for a non-repeated field, and
+  uses the last one.
+
   Args:
     lines: An iterable of lines of a message's text representation.
     message: A protocol buffer message to merge into.
@@ -601,22 +637,12 @@ class _Parser(object):
     self.allow_field_number = allow_field_number
     self.descriptor_pool = descriptor_pool
 
-  def ParseFromString(self, text, message):
-    """Parses a text representation of a protocol message into a message."""
-    if not isinstance(text, str):
-      text = text.decode('utf-8')
-    return self.ParseLines(text.split('\n'), message)
-
   def ParseLines(self, lines, message):
     """Parses a text representation of a protocol message into a message."""
     self._allow_multiple_scalars = False
     self._ParseOrMerge(lines, message)
     return message
 
-  def MergeFromString(self, text, message):
-    """Merges a text representation of a protocol message into a message."""
-    return self._MergeLines(text.split('\n'), message)
-
   def MergeLines(self, lines, message):
     """Merges a text representation of a protocol message into a message."""
     self._allow_multiple_scalars = True
@@ -633,7 +659,14 @@ class _Parser(object):
     Raises:
       ParseError: On text parsing problems.
     """
-    tokenizer = Tokenizer(lines)
+    # Tokenize expects native str lines.
+    if six.PY2:
+      str_lines = (line if isinstance(line, str) else line.encode('utf-8')
+                   for line in lines)
+    else:
+      str_lines = (line if isinstance(line, str) else line.decode('utf-8')
+                   for line in lines)
+    tokenizer = Tokenizer(str_lines)
     while not tokenizer.AtEnd():
       self._MergeField(tokenizer, message)
 
@@ -1019,7 +1052,9 @@ class Tokenizer(object):
       r'[a-zA-Z_][0-9a-zA-Z_+-]*',  # an identifier
       r'([0-9+-]|(\.[0-9]))[0-9a-zA-Z_.+-]*',  # a number
   ] + [  # quoted str for each quote mark
-      r'{qt}([^{qt}\n\\]|\\.)*({qt}|\\?$)'.format(qt=mark) for mark in _QUOTES
+      # Avoid backtracking! https://stackoverflow.com/a/844267
+      r'{qt}[^{qt}\n\\]*((\\.)+[^{qt}\n\\]*)*({qt}|\\?$)'.format(qt=mark)
+      for mark in _QUOTES
   ]))
 
   _IDENTIFIER = re.compile(r'[^\d\W]\w*')
@@ -1316,7 +1351,8 @@ class Tokenizer(object):
 
   def ParseError(self, message):
     """Creates and *returns* a ParseError for the current token."""
-    return ParseError(message, self._line + 1, self._column + 1)
+    return ParseError('\'' + self._current_line + '\': ' + message,
+                      self._line + 1, self._column + 1)
 
   def _StringParseError(self, e):
     return self.ParseError('Couldn\'t parse string: ' + str(e))
@@ -1490,6 +1526,12 @@ def _ParseAbstractInteger(text, is_long=False):
     ValueError: Thrown Iff the text is not a valid integer.
   """
   # Do the actual parsing. Exception handling is propagated to caller.
+  orig_text = text
+  c_octal_match = re.match(r'(-?)0(\d+)$', text)
+  if c_octal_match:
+    # Python 3 no longer supports 0755 octal syntax without the 'o', so
+    # we always use the '0o' prefix for multi-digit numbers starting with 0.
+    text = c_octal_match.group(1) + '0o' + c_octal_match.group(2)
   try:
     # We force 32-bit values to int and 64-bit values to long to make
     # alternate implementations where the distinction is more significant
@@ -1499,7 +1541,7 @@ def _ParseAbstractInteger(text, is_long=False):
     else:
       return int(text, 0)
   except ValueError:
-    raise ValueError('Couldn\'t parse integer: %s' % text)
+    raise ValueError('Couldn\'t parse integer: %s' % orig_text)
 
 
 def ParseFloat(text):