[SPARK-5464] Fix help() for Python DataFrame instances

This fixes an exception that prevented users from calling `help()` on Python DataFrame instances.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #4278 from JoshRosen/SPARK-5464-python-dataframe-help-command and squashes the following commits:

08f95f7 [Josh Rosen] Fix exception when calling help() on Python DataFrame instances

1 files changed, 3 insertions, 3 deletions

diff --git a/python/pyspark/sql.py b/python/pyspark/sql.py
index e636f992ec..3f2d7ac825 100644
--- a/python/pyspark/sql.py
+++ b/python/pyspark/sql.py
@@ -2136,9 +2136,9 @@ class DataFrame(object):
 
     def __getattr__(self, name):
         """ Return the column by given name """
-        if isinstance(name, basestring):
-            return Column(self._jdf.apply(name))
-        raise AttributeError
+        if name.startswith("__"):
+            raise AttributeError(name)
+        return Column(self._jdf.apply(name))
 
     def alias(self, name):
         """ Alias the current DataFrame """