[SPARK-7380] [MLLIB] pipeline stages should be copyable in Python

This PR makes pipeline stages in Python copyable and hence simplifies some implementations. It also includes the following changes:

1. Rename `paramMap` and `defaultParamMap` to `_paramMap` and `_defaultParamMap`, respectively.
2. Accept a list of param maps in `fit`.
3. Use parent uid and name to identify param.

jkbradley

Author: Xiangrui Meng <meng@databricks.com>
Author: Joseph K. Bradley <joseph@databricks.com>

Closes #6088 from mengxr/SPARK-7380 and squashes the following commits:

413c463 [Xiangrui Meng] remove unnecessary doc
4159f35 [Xiangrui Meng] Merge remote-tracking branch 'apache/master' into SPARK-7380
611c719 [Xiangrui Meng] fix python style
68862b8 [Xiangrui Meng] update _java_obj initialization
927ad19 [Xiangrui Meng] fix ml/tests.py
0138fc3 [Xiangrui Meng] update feature transformers and fix a bug in RegexTokenizer
9ca44fb [Xiangrui Meng] simplify Java wrappers and add tests
c7d84ef [Xiangrui Meng] update ml/tests.py to test copy params
7e0d27f [Xiangrui Meng] merge master
46840fb [Xiangrui Meng] update wrappers
b6db1ed [Xiangrui Meng] update all self.paramMap to self._paramMap
46cb6ed [Xiangrui Meng] merge master
a163413 [Xiangrui Meng] fix style
1042e80 [Xiangrui Meng] Merge remote-tracking branch 'apache/master' into SPARK-7380
9630eae [Xiangrui Meng] fix Identifiable._randomUID
13bd70a [Xiangrui Meng] update ml/tests.py
64a536c [Xiangrui Meng] use _fit/_transform/_evaluate to simplify the impl
02abf13 [Xiangrui Meng] Merge remote-tracking branch 'apache/master' into copyable-python
66ce18c [Joseph K. Bradley] some cleanups before sending to Xiangrui
7431272 [Joseph K. Bradley] Rebased with master

1 files changed, 10 insertions, 3 deletions

diff --git a/python/pyspark/ml/util.py b/python/pyspark/ml/util.py
index d3cb100a9e..cee9d67b05 100644
--- a/python/pyspark/ml/util.py
+++ b/python/pyspark/ml/util.py
@@ -39,9 +39,16 @@ class Identifiable(object):
     """
 
     def __init__(self):
-        #: A unique id for the object. The default implementation
-        #: concatenates the class name, "_", and 8 random hex chars.
-        self.uid = type(self).__name__ + "_" + uuid.uuid4().hex[:8]
+        #: A unique id for the object.
+        self.uid = self._randomUID()
 
     def __repr__(self):
         return self.uid
+
+    @classmethod
+    def _randomUID(cls):
+        """
+        Generate a unique id for the object. The default implementation
+        concatenates the class name, "_", and 12 random hex chars.
+        """
+        return cls.__name__ + "_" + uuid.uuid4().hex[12:]