Down-integrate from google3.

23 files changed, 969 insertions, 665 deletions

diff --git a/python/google/protobuf/internal/containers.py b/python/google/protobuf/internal/containers.py
index 72c2fa01..9c8275eb 100755
--- a/python/google/protobuf/internal/containers.py
+++ b/python/google/protobuf/internal/containers.py
@@ -41,6 +41,7 @@ are:
 
 __author__ = 'petar@google.com (Petar Petrov)'
 
+import collections
 import sys
 
 if sys.version_info[0] < 3:
@@ -63,7 +64,6 @@ if sys.version_info[0] < 3:
   # Note: deriving from object is critical.  It is the only thing that makes
   # this a true type, allowing us to derive from it in C++ cleanly and making
   # __slots__ properly disallow arbitrary element assignment.
-  from collections import Mapping as _Mapping
 
   class Mapping(object):
     __slots__ = ()
@@ -106,7 +106,7 @@ if sys.version_info[0] < 3:
     __hash__ = None
 
     def __eq__(self, other):
-      if not isinstance(other, _Mapping):
+      if not isinstance(other, collections.Mapping):
         return NotImplemented
       return dict(self.items()) == dict(other.items())
 
@@ -173,12 +173,13 @@ if sys.version_info[0] < 3:
         self[key] = default
       return default
 
-  _Mapping.register(Mapping)
+  collections.Mapping.register(Mapping)
+  collections.MutableMapping.register(MutableMapping)
 
 else:
   # In Python 3 we can just use MutableMapping directly, because it defines
   # __slots__.
-  from collections import MutableMapping
+  MutableMapping = collections.MutableMapping
 
 
 class BaseContainer(object):
@@ -336,6 +337,8 @@ class RepeatedScalarFieldContainer(BaseContainer):
     # We are presumably comparing against some other sequence type.
     return other == self._values
 
+collections.MutableSequence.register(BaseContainer)
+
 
 class RepeatedCompositeFieldContainer(BaseContainer):
 
diff --git a/python/google/protobuf/internal/generator_test.py b/python/google/protobuf/internal/generator_test.py
index 5c07cbe6..c30f633d 100755
--- a/python/google/protobuf/internal/generator_test.py
+++ b/python/google/protobuf/internal/generator_test.py
@@ -47,6 +47,7 @@ from google.protobuf import unittest_custom_options_pb2
 from google.protobuf import unittest_import_pb2
 from google.protobuf import unittest_import_public_pb2
 from google.protobuf import unittest_mset_pb2
+from google.protobuf import unittest_mset_wire_format_pb2
 from google.protobuf import unittest_no_generic_services_pb2
 from google.protobuf import unittest_pb2
 from google.protobuf import service
@@ -142,7 +143,7 @@ class GeneratorTest(unittest.TestCase):
     self.assertTrue(not non_extension_descriptor.is_extension)
 
   def testOptions(self):
-    proto = unittest_mset_pb2.TestMessageSet()
+    proto = unittest_mset_wire_format_pb2.TestMessageSet()
     self.assertTrue(proto.DESCRIPTOR.GetOptions().message_set_wire_format)
 
   def testMessageWithCustomOptions(self):
diff --git a/python/google/protobuf/internal/message_test.py b/python/google/protobuf/internal/message_test.py
index 320ff0d2..62abf1be 100755
--- a/python/google/protobuf/internal/message_test.py
+++ b/python/google/protobuf/internal/message_test.py
@@ -43,6 +43,7 @@ abstract interface.
 
 __author__ = 'gps@google.com (Gregory P. Smith)'
 
+import collections
 import copy
 import math
 import operator
@@ -56,6 +57,7 @@ from google.protobuf import map_unittest_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 packed_field_test_pb2
 from google.protobuf.internal import test_util
 from google.protobuf import message
 
@@ -421,6 +423,31 @@ class MessageTest(unittest.TestCase):
     self.assertEqual(message.repeated_nested_message[4].bb, 5)
     self.assertEqual(message.repeated_nested_message[5].bb, 6)
 
+  def testSortingRepeatedCompositeFieldsStable(self, message_module):
+    """Check passing a custom comparator to sort a repeated composite field."""
+    message = message_module.TestAllTypes()
+
+    message.repeated_nested_message.add().bb = 21
+    message.repeated_nested_message.add().bb = 20
+    message.repeated_nested_message.add().bb = 13
+    message.repeated_nested_message.add().bb = 33
+    message.repeated_nested_message.add().bb = 11
+    message.repeated_nested_message.add().bb = 24
+    message.repeated_nested_message.add().bb = 10
+    message.repeated_nested_message.sort(key=lambda z: z.bb // 10)
+    self.assertEquals(
+        [13, 11, 10, 21, 20, 24, 33],
+        [n.bb for n in message.repeated_nested_message])
+
+    # Make sure that for the C++ implementation, the underlying fields
+    # are actually reordered.
+    pb = message.SerializeToString()
+    message.Clear()
+    message.MergeFromString(pb)
+    self.assertEquals(
+        [13, 11, 10, 21, 20, 24, 33],
+        [n.bb for n in message.repeated_nested_message])
+
   def testRepeatedCompositeFieldSortArguments(self, message_module):
     """Check sorting a repeated composite field using list.sort() arguments."""
     message = message_module.TestAllTypes()
@@ -514,6 +541,12 @@ class MessageTest(unittest.TestCase):
 
     # TODO(anuraag): Implement extensiondict comparison in C++ and then add test
 
+  def testRepeatedFieldsAreSequences(self, message_module):
+    m = message_module.TestAllTypes()
+    self.assertIsInstance(m.repeated_int32, collections.MutableSequence)
+    self.assertIsInstance(m.repeated_nested_message,
+                          collections.MutableSequence)
+
   def ensureNestedMessageExists(self, msg, attribute):
     """Make sure that a nested message object exists.
 
@@ -556,6 +589,18 @@ class MessageTest(unittest.TestCase):
     self.assertFalse(m.HasField('oneof_uint32'))
     self.assertTrue(m.HasField('oneof_string'))
 
+    # Read nested message accessor without accessing submessage.
+    m.oneof_nested_message
+    self.assertEqual('oneof_string', m.WhichOneof('oneof_field'))
+    self.assertTrue(m.HasField('oneof_string'))
+    self.assertFalse(m.HasField('oneof_nested_message'))
+
+    # Read accessor of nested message without accessing submessage.
+    m.oneof_nested_message.bb
+    self.assertEqual('oneof_string', m.WhichOneof('oneof_field'))
+    self.assertTrue(m.HasField('oneof_string'))
+    self.assertFalse(m.HasField('oneof_nested_message'))
+
     m.oneof_nested_message.bb = 11
     self.assertEqual('oneof_nested_message', m.WhichOneof('oneof_field'))
     self.assertFalse(m.HasField('oneof_string'))
@@ -1583,6 +1628,21 @@ class Proto3Test(unittest.TestCase):
     del msg.map_int32_int32[4]
     self.assertEqual(0, len(msg.map_int32_int32))
 
+  def testMapsAreMapping(self):
+    msg = map_unittest_pb2.TestMap()
+    self.assertIsInstance(msg.map_int32_int32, collections.Mapping)
+    self.assertIsInstance(msg.map_int32_int32, collections.MutableMapping)
+    self.assertIsInstance(msg.map_int32_foreign_message, collections.Mapping)
+    self.assertIsInstance(msg.map_int32_foreign_message,
+                          collections.MutableMapping)
+
+  def testMapFindInitializationErrorsSmokeTest(self):
+    msg = map_unittest_pb2.TestMap()
+    msg.map_string_string['abc'] = '123'
+    msg.map_int32_int32[35] = 64
+    msg.map_string_foreign_message['foo'].c = 5
+    self.assertEqual(0, len(msg.FindInitializationErrors()))
+
 
 
 class ValidTypeNamesTest(unittest.TestCase):
@@ -1606,6 +1666,61 @@ class ValidTypeNamesTest(unittest.TestCase):
     self.assertImportFromName(pb.repeated_int32, 'Scalar')
     self.assertImportFromName(pb.repeated_nested_message, 'Composite')
 
+class PackedFieldTest(unittest.TestCase):
+
+  def setMessage(self, message):
+    message.repeated_int32.append(1)
+    message.repeated_int64.append(1)
+    message.repeated_uint32.append(1)
+    message.repeated_uint64.append(1)
+    message.repeated_sint32.append(1)
+    message.repeated_sint64.append(1)
+    message.repeated_fixed32.append(1)
+    message.repeated_fixed64.append(1)
+    message.repeated_sfixed32.append(1)
+    message.repeated_sfixed64.append(1)
+    message.repeated_float.append(1.0)
+    message.repeated_double.append(1.0)
+    message.repeated_bool.append(True)
+    message.repeated_nested_enum.append(1)
+
+  def testPackedFields(self):
+    message = packed_field_test_pb2.TestPackedTypes()
+    self.setMessage(message)
+    golden_data = (b'\x0A\x01\x01'
+                   b'\x12\x01\x01'
+                   b'\x1A\x01\x01'
+                   b'\x22\x01\x01'
+                   b'\x2A\x01\x02'
+                   b'\x32\x01\x02'
+                   b'\x3A\x04\x01\x00\x00\x00'
+                   b'\x42\x08\x01\x00\x00\x00\x00\x00\x00\x00'
+                   b'\x4A\x04\x01\x00\x00\x00'
+                   b'\x52\x08\x01\x00\x00\x00\x00\x00\x00\x00'
+                   b'\x5A\x04\x00\x00\x80\x3f'
+                   b'\x62\x08\x00\x00\x00\x00\x00\x00\xf0\x3f'
+                   b'\x6A\x01\x01'
+                   b'\x72\x01\x01')
+    self.assertEqual(golden_data, message.SerializeToString())
+
+  def testUnpackedFields(self):
+    message = packed_field_test_pb2.TestUnpackedTypes()
+    self.setMessage(message)
+    golden_data = (b'\x08\x01'
+                   b'\x10\x01'
+                   b'\x18\x01'
+                   b'\x20\x01'
+                   b'\x28\x02'
+                   b'\x30\x02'
+                   b'\x3D\x01\x00\x00\x00'
+                   b'\x41\x01\x00\x00\x00\x00\x00\x00\x00'
+                   b'\x4D\x01\x00\x00\x00'
+                   b'\x51\x01\x00\x00\x00\x00\x00\x00\x00'
+                   b'\x5D\x00\x00\x80\x3f'
+                   b'\x61\x00\x00\x00\x00\x00\x00\xf0\x3f'
+                   b'\x68\x01'
+                   b'\x70\x01')
+    self.assertEqual(golden_data, message.SerializeToString())
 
 if __name__ == '__main__':
   unittest.main()
diff --git a/python/google/protobuf/internal/packed_field_test.proto b/python/google/protobuf/internal/packed_field_test.proto
index e69de29b..0dfdc10a 100644
--- a/python/google/protobuf/internal/packed_field_test.proto
+++ b/python/google/protobuf/internal/packed_field_test.proto
@@ -0,0 +1,73 @@
+// 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 = "proto3";
+
+package google.protobuf.python.internal;
+
+message TestPackedTypes {
+  enum NestedEnum {
+    FOO = 0;
+    BAR = 1;
+    BAZ = 2;
+  }
+
+  repeated    int32 repeated_int32    =  1;
+  repeated    int64 repeated_int64    =  2;
+  repeated   uint32 repeated_uint32   =  3;
+  repeated   uint64 repeated_uint64   =  4;
+  repeated   sint32 repeated_sint32   =  5;
+  repeated   sint64 repeated_sint64   =  6;
+  repeated  fixed32 repeated_fixed32  =  7;
+  repeated  fixed64 repeated_fixed64  =  8;
+  repeated sfixed32 repeated_sfixed32 =  9;
+  repeated sfixed64 repeated_sfixed64 = 10;
+  repeated    float repeated_float    = 11;
+  repeated   double repeated_double   = 12;
+  repeated     bool repeated_bool     = 13;
+  repeated NestedEnum repeated_nested_enum = 14;
+}
+
+message TestUnpackedTypes {
+  repeated    int32 repeated_int32    =  1 [packed = false];
+  repeated    int64 repeated_int64    =  2 [packed = false];
+  repeated   uint32 repeated_uint32   =  3 [packed = false];
+  repeated   uint64 repeated_uint64   =  4 [packed = false];
+  repeated   sint32 repeated_sint32   =  5 [packed = false];
+  repeated   sint64 repeated_sint64   =  6 [packed = false];
+  repeated  fixed32 repeated_fixed32  =  7 [packed = false];
+  repeated  fixed64 repeated_fixed64  =  8 [packed = false];
+  repeated sfixed32 repeated_sfixed32 =  9 [packed = false];
+  repeated sfixed64 repeated_sfixed64 = 10 [packed = false];
+  repeated    float repeated_float    = 11 [packed = false];
+  repeated   double repeated_double   = 12 [packed = false];
+  repeated     bool repeated_bool     = 13 [packed = false];
+  repeated TestPackedTypes.NestedEnum repeated_nested_enum = 14 [packed = false];
+}
diff --git a/python/google/protobuf/internal/python_message.py b/python/google/protobuf/internal/python_message.py
index ca9f7675..a3e98467 100755
--- a/python/google/protobuf/internal/python_message.py
+++ b/python/google/protobuf/internal/python_message.py
@@ -85,34 +85,108 @@ from google.protobuf import text_format
 _FieldDescriptor = descriptor_mod.FieldDescriptor
 
 
-def NewMessage(bases, descriptor, dictionary):
-  _AddClassAttributesForNestedExtensions(descriptor, dictionary)
-  _AddSlots(descriptor, dictionary)
-  return bases
-
-
-def InitMessage(descriptor, cls):
-  cls._decoders_by_tag = {}
-  cls._extensions_by_name = {}
-  cls._extensions_by_number = {}
-  if (descriptor.has_options and
-      descriptor.GetOptions().message_set_wire_format):
-    cls._decoders_by_tag[decoder.MESSAGE_SET_ITEM_TAG] = (
-        decoder.MessageSetItemDecoder(cls._extensions_by_number), None)
-
-  # Attach stuff to each FieldDescriptor for quick lookup later on.
-  for field in descriptor.fields:
-    _AttachFieldHelpers(cls, field)
+class GeneratedProtocolMessageType(type):
+
+  """Metaclass for protocol message classes created at runtime from Descriptors.
+
+  We add implementations for all methods described in the Message class.  We
+  also create properties to allow getting/setting all fields in the protocol
+  message.  Finally, we create slots to prevent users from accidentally
+  "setting" nonexistent fields in the protocol message, which then wouldn't get
+  serialized / deserialized properly.
+
+  The protocol compiler currently uses this metaclass to create protocol
+  message classes at runtime.  Clients can also manually create their own
+  classes at runtime, as in this example:
+
+  mydescriptor = Descriptor(.....)
+  class MyProtoClass(Message):
+    __metaclass__ = GeneratedProtocolMessageType
+    DESCRIPTOR = mydescriptor
+  myproto_instance = MyProtoClass()
+  myproto.foo_field = 23
+  ...
+
+  The above example will not work for nested types. If you wish to include them,
+  use reflection.MakeClass() instead of manually instantiating the class in
+  order to create the appropriate class structure.
+  """
+
+  # Must be consistent with the protocol-compiler code in
+  # proto2/compiler/internal/generator.*.
+  _DESCRIPTOR_KEY = 'DESCRIPTOR'
+
+  def __new__(cls, name, bases, dictionary):
+    """Custom allocation for runtime-generated class types.
+
+    We override __new__ because this is apparently the only place
+    where we can meaningfully set __slots__ on the class we're creating(?).
+    (The interplay between metaclasses and slots is not very well-documented).
+
+    Args:
+      name: Name of the class (ignored, but required by the
+        metaclass protocol).
+      bases: Base classes of the class we're constructing.
+        (Should be message.Message).  We ignore this field, but
+        it's required by the metaclass protocol
+      dictionary: The class dictionary of the class we're
+        constructing.  dictionary[_DESCRIPTOR_KEY] must contain
+        a Descriptor object describing this protocol message
+        type.
+
+    Returns:
+      Newly-allocated class.
+    """
+    descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
+    _AddClassAttributesForNestedExtensions(descriptor, dictionary)
+    _AddSlots(descriptor, dictionary)
+
+    superclass = super(GeneratedProtocolMessageType, cls)
+    new_class = superclass.__new__(cls, name, bases, dictionary)
+    return new_class
+
+  def __init__(cls, name, bases, dictionary):
+    """Here we perform the majority of our work on the class.
+    We add enum getters, an __init__ method, implementations
+    of all Message methods, and properties for all fields
+    in the protocol type.
 
-  descriptor._concrete_class = cls  # pylint: disable=protected-access
-  _AddEnumValues(descriptor, cls)
-  _AddInitMethod(descriptor, cls)
-  _AddPropertiesForFields(descriptor, cls)
-  _AddPropertiesForExtensions(descriptor, cls)
-  _AddStaticMethods(cls)
-  _AddMessageMethods(descriptor, cls)
-  _AddPrivateHelperMethods(descriptor, cls)
-  copyreg.pickle(cls, lambda obj: (cls, (), obj.__getstate__()))
+    Args:
+      name: Name of the class (ignored, but required by the
+        metaclass protocol).
+      bases: Base classes of the class we're constructing.
+        (Should be message.Message).  We ignore this field, but
+        it's required by the metaclass protocol
+      dictionary: The class dictionary of the class we're
+        constructing.  dictionary[_DESCRIPTOR_KEY] must contain
+        a Descriptor object describing this protocol message
+        type.
+    """
+    descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
+    cls._decoders_by_tag = {}
+    cls._extensions_by_name = {}
+    cls._extensions_by_number = {}
+    if (descriptor.has_options and
+        descriptor.GetOptions().message_set_wire_format):
+      cls._decoders_by_tag[decoder.MESSAGE_SET_ITEM_TAG] = (
+          decoder.MessageSetItemDecoder(cls._extensions_by_number), None)
+
+    # Attach stuff to each FieldDescriptor for quick lookup later on.
+    for field in descriptor.fields:
+      _AttachFieldHelpers(cls, field)
+
+    descriptor._concrete_class = cls  # pylint: disable=protected-access
+    _AddEnumValues(descriptor, cls)
+    _AddInitMethod(descriptor, cls)
+    _AddPropertiesForFields(descriptor, cls)
+    _AddPropertiesForExtensions(descriptor, cls)
+    _AddStaticMethods(cls)
+    _AddMessageMethods(descriptor, cls)
+    _AddPrivateHelperMethods(descriptor, cls)
+    copyreg.pickle(cls, lambda obj: (cls, (), obj.__getstate__()))
+
+    superclass = super(GeneratedProtocolMessageType, cls)
+    superclass.__init__(name, bases, dictionary)
 
 
 # Stateless helpers for GeneratedProtocolMessageType below.
@@ -362,9 +436,10 @@ def _DefaultValueConstructorForField(field):
     message_type = field.message_type
     def MakeSubMessageDefault(message):
       result = message_type._concrete_class()
-      result._SetListener(message._listener_for_children)
-      if field.containing_oneof:
-        message._UpdateOneofState(field)
+      result._SetListener(
+          _OneofListener(message, field)
+          if field.containing_oneof is not None
+          else message._listener_for_children)
       return result
     return MakeSubMessageDefault
 
@@ -634,21 +709,11 @@ def _AddPropertiesForNonRepeatedCompositeField(field, cls):
   proto_field_name = field.name
   property_name = _PropertyName(proto_field_name)
 
-  # TODO(komarek): Can anyone explain to me why we cache the message_type this
-  # way, instead of referring to field.message_type inside of getter(self)?
-  # What if someone sets message_type later on (which makes for simpler
-  # dyanmic proto descriptor and class creation code).
-  message_type = field.message_type
-
   def getter(self):
     field_value = self._fields.get(field)
     if field_value is None:
       # Construct a new object to represent this field.
-      field_value = message_type._concrete_class()  # use field.message_type?
-      field_value._SetListener(
-          _OneofListener(self, field)
-          if field.containing_oneof is not None
-          else self._listener_for_children)
+      field_value = field._default_constructor(self)
 
       # Atomically check if another thread has preempted us and, if not, swap
       # in the new object we just created.  If someone has preempted us, we
@@ -1121,7 +1186,7 @@ def _AddIsInitializedMethod(message_descriptor, cls):
           if _IsMessageMapField(field):
             for key in value:
               element = value[key]
-              prefix = "%s[%d]." % (name, key)
+              prefix = "%s[%s]." % (name, key)
               sub_errors = element.FindInitializationErrors()
               errors += [prefix + error for error in sub_errors]
           else:
@@ -1173,8 +1238,6 @@ def _AddMergeFromMethod(cls):
             # Construct a new object to represent this field.
             field_value = field._default_constructor(self)
             fields[field] = field_value
-            if field.containing_oneof:
-              self._UpdateOneofState(field)
           field_value.MergeFrom(value)
       else:
         self._fields[field] = value
diff --git a/python/google/protobuf/internal/reflection_test.py b/python/google/protobuf/internal/reflection_test.py
index 4eca4989..ef1ced4e 100755
--- a/python/google/protobuf/internal/reflection_test.py
+++ b/python/google/protobuf/internal/reflection_test.py
@@ -52,6 +52,7 @@ from google.protobuf import text_format
 from google.protobuf.internal import api_implementation
 from google.protobuf.internal import more_extensions_pb2
 from google.protobuf.internal import more_messages_pb2
+from google.protobuf.internal import message_set_extensions_pb2
 from google.protobuf.internal import wire_format
 from google.protobuf.internal import test_util
 from google.protobuf.internal import decoder
@@ -1682,8 +1683,8 @@ class ReflectionTest(unittest.TestCase):
     proto.optional_string = 'abc'
 
   def testStringUTF8Serialization(self):
-    proto = unittest_mset_pb2.TestMessageSet()
-    extension_message = unittest_mset_pb2.TestMessageSetExtension2
+    proto = message_set_extensions_pb2.TestMessageSet()
+    extension_message = message_set_extensions_pb2.TestMessageSetExtension2
     extension = extension_message.message_set_extension
 
     test_utf8 = u'Тест'
@@ -1703,15 +1704,14 @@ class ReflectionTest(unittest.TestCase):
     bytes_read = raw.MergeFromString(serialized)
     self.assertEqual(len(serialized), bytes_read)
 
-    message2 = unittest_mset_pb2.TestMessageSetExtension2()
+    message2 = message_set_extensions_pb2.TestMessageSetExtension2()
 
     self.assertEqual(1, len(raw.item))
     # Check that the type_id is the same as the tag ID in the .proto file.
-    self.assertEqual(raw.item[0].type_id, 1547769)
+    self.assertEqual(raw.item[0].type_id, 98418634)
 
     # Check the actual bytes on the wire.
-    self.assertTrue(
-        raw.item[0].message.endswith(test_utf8_bytes))
+    self.assertTrue(raw.item[0].message.endswith(test_utf8_bytes))
     bytes_read = message2.MergeFromString(raw.item[0].message)
     self.assertEqual(len(raw.item[0].message), bytes_read)
 
@@ -2395,9 +2395,9 @@ class SerializationTest(unittest.TestCase):
     self.assertEqual(42, second_proto.optional_nested_message.bb)
 
   def testMessageSetWireFormat(self):
-    proto = unittest_mset_pb2.TestMessageSet()
-    extension_message1 = unittest_mset_pb2.TestMessageSetExtension1
-    extension_message2 = unittest_mset_pb2.TestMessageSetExtension2
+    proto = message_set_extensions_pb2.TestMessageSet()
+    extension_message1 = message_set_extensions_pb2.TestMessageSetExtension1
+    extension_message2 = message_set_extensions_pb2.TestMessageSetExtension2
     extension1 = extension_message1.message_set_extension
     extension2 = extension_message2.message_set_extension
     proto.Extensions[extension1].i = 123
@@ -2415,20 +2415,20 @@ class SerializationTest(unittest.TestCase):
         raw.MergeFromString(serialized))
     self.assertEqual(2, len(raw.item))
 
-    message1 = unittest_mset_pb2.TestMessageSetExtension1()
+    message1 = message_set_extensions_pb2.TestMessageSetExtension1()
     self.assertEqual(
         len(raw.item[0].message),
         message1.MergeFromString(raw.item[0].message))
     self.assertEqual(123, message1.i)
 
-    message2 = unittest_mset_pb2.TestMessageSetExtension2()
+    message2 = message_set_extensions_pb2.TestMessageSetExtension2()
     self.assertEqual(
         len(raw.item[1].message),
         message2.MergeFromString(raw.item[1].message))
     self.assertEqual('foo', message2.str)
 
     # Deserialize using the MessageSet wire format.
-    proto2 = unittest_mset_pb2.TestMessageSet()
+    proto2 = message_set_extensions_pb2.TestMessageSet()
     self.assertEqual(
         len(serialized),
         proto2.MergeFromString(serialized))
@@ -2446,37 +2446,37 @@ class SerializationTest(unittest.TestCase):
 
     # Add an item.
     item = raw.item.add()
-    item.type_id = 1545008
-    extension_message1 = unittest_mset_pb2.TestMessageSetExtension1
-    message1 = unittest_mset_pb2.TestMessageSetExtension1()
+    item.type_id = 98418603
+    extension_message1 = message_set_extensions_pb2.TestMessageSetExtension1
+    message1 = message_set_extensions_pb2.TestMessageSetExtension1()
     message1.i = 12345
     item.message = message1.SerializeToString()
 
     # Add a second, unknown extension.
     item = raw.item.add()
-    item.type_id = 1545009
-    extension_message1 = unittest_mset_pb2.TestMessageSetExtension1
-    message1 = unittest_mset_pb2.TestMessageSetExtension1()
+    item.type_id = 98418604
+    extension_message1 = message_set_extensions_pb2.TestMessageSetExtension1
+    message1 = message_set_extensions_pb2.TestMessageSetExtension1()
     message1.i = 12346
     item.message = message1.SerializeToString()
 
     # Add another unknown extension.
     item = raw.item.add()
-    item.type_id = 1545010
-    message1 = unittest_mset_pb2.TestMessageSetExtension2()
+    item.type_id = 98418605
+    message1 = message_set_extensions_pb2.TestMessageSetExtension2()
     message1.str = 'foo'
     item.message = message1.SerializeToString()
 
     serialized = raw.SerializeToString()
 
     # Parse message using the message set wire format.
-    proto = unittest_mset_pb2.TestMessageSet()
+    proto = message_set_extensions_pb2.TestMessageSet()
     self.assertEqual(
         len(serialized),
         proto.MergeFromString(serialized))
 
     # Check that the message parsed well.
-    extension_message1 = unittest_mset_pb2.TestMessageSetExtension1
+    extension_message1 = message_set_extensions_pb2.TestMessageSetExtension1
     extension1 = extension_message1.message_set_extension
     self.assertEquals(12345, proto.Extensions[extension1].i)
 
@@ -2805,7 +2805,7 @@ class SerializationTest(unittest.TestCase):
 class OptionsTest(unittest.TestCase):
 
   def testMessageOptions(self):
-    proto = unittest_mset_pb2.TestMessageSet()
+    proto = message_set_extensions_pb2.TestMessageSet()
     self.assertEqual(True,
                      proto.DESCRIPTOR.GetOptions().message_set_wire_format)
     proto = unittest_pb2.TestAllTypes()
@@ -2824,7 +2824,7 @@ class OptionsTest(unittest.TestCase):
     proto.packed_double.append(3.0)
     for field_descriptor, _ in proto.ListFields():
       self.assertEqual(True, field_descriptor.GetOptions().packed)
-      self.assertEqual(reflection._FieldDescriptor.LABEL_REPEATED,
+      self.assertEqual(descriptor.FieldDescriptor.LABEL_REPEATED,
                        field_descriptor.label)
 
 
diff --git a/python/google/protobuf/internal/test_util.py b/python/google/protobuf/internal/test_util.py
index fec65382..ac88fa81 100755
--- a/python/google/protobuf/internal/test_util.py
+++ b/python/google/protobuf/internal/test_util.py
@@ -604,7 +604,8 @@ def GoldenFile(filename):
 
   # Search internally.
   path = '.'
-  full_path = os.path.join(path, 'third_party/py/google/protobuf/testdata', filename)
+  full_path = os.path.join(path, 'third_party/py/google/protobuf/testdata',
+                           filename)
   if os.path.exists(full_path):
     # Found it.  Load the golden file from the testdata directory.
     return open(full_path, 'rb')
diff --git a/python/google/protobuf/internal/text_format_test.py b/python/google/protobuf/internal/text_format_test.py
index 06bd1ee5..00e67654 100755
--- a/python/google/protobuf/internal/text_format_test.py
+++ b/python/google/protobuf/internal/text_format_test.py
@@ -35,6 +35,7 @@
 __author__ = 'kenton@google.com (Kenton Varda)'
 
 import re
+import string
 import unittest
 
 import unittest
@@ -497,6 +498,36 @@ class OnlyWorksWithProto2RightNowTests(TextFormatBase):
         '  }\n'
         '}\n')
 
+  def testMapOrderEnforcement(self):
+    message = map_unittest_pb2.TestMap()
+    for letter in string.ascii_uppercase[13:26]:
+      message.map_string_string[letter] = 'dummy'
+    for letter in reversed(string.ascii_uppercase[0:13]):
+      message.map_string_string[letter] = 'dummy'
+    golden = ''.join((
+        'map_string_string {\n  key: "%c"\n  value: "dummy"\n}\n' % (letter,)
+        for letter in string.ascii_uppercase))
+    self.CompareToGoldenText(text_format.MessageToString(message), golden)
+
+  def testMapOrderSemantics(self):
+    golden_lines = self.ReadGolden('map_test_data.txt')
+    # The C++ implementation emits defaulted-value fields, while the Python
+    # implementation does not.  Adjusting for this is awkward, but it is
+    # valuable to test against a common golden file.
+    line_blacklist = ('  key: 0\n',
+                      '  value: 0\n',
+                      '  key: false\n',
+                      '  value: false\n')
+    golden_lines = [line for line in golden_lines if line not in line_blacklist]
+
+    message = map_unittest_pb2.TestMap()
+    text_format.ParseLines(golden_lines, message)
+    candidate = text_format.MessageToString(message)
+    # The Python implementation emits "1.0" for the double value that the C++
+    # implementation emits as "1".
+    candidate = candidate.replace('1.0', '1', 2)
+    self.assertMultiLineEqual(candidate, ''.join(golden_lines))
+
 
 # Tests of proto2-only features (MessageSet, extensions, etc.).
 class Proto2Tests(TextFormatBase):
diff --git a/python/google/protobuf/internal/unknown_fields_test.py b/python/google/protobuf/internal/unknown_fields_test.py
index 1b81ae79..0dda805b 100755
--- a/python/google/protobuf/internal/unknown_fields_test.py
+++ b/python/google/protobuf/internal/unknown_fields_test.py
@@ -41,11 +41,18 @@ 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 encoder
+from google.protobuf.internal import message_set_extensions_pb2
 from google.protobuf.internal import missing_enum_values_pb2
 from google.protobuf.internal import test_util
 from google.protobuf.internal import type_checkers
 
 
+def SkipIfCppImplementation(func):
+  return unittest.skipIf(
+      api_implementation.Type() == 'cpp' and api_implementation.Version() == 2,
+      'C++ implementation does not expose unknown fields to Python')(func)
+
+
 class UnknownFieldsTest(unittest.TestCase):
 
   def setUp(self):
@@ -83,15 +90,15 @@ class UnknownFieldsTest(unittest.TestCase):
 
     # Add an unknown extension.
     item = raw.item.add()
-    item.type_id = 1545009
-    message1 = unittest_mset_pb2.TestMessageSetExtension1()
+    item.type_id = 98418603
+    message1 = message_set_extensions_pb2.TestMessageSetExtension1()
     message1.i = 12345
     item.message = message1.SerializeToString()
 
     serialized = raw.SerializeToString()
 
     # Parse message using the message set wire format.
-    proto = unittest_mset_pb2.TestMessageSet()
+    proto = message_set_extensions_pb2.TestMessageSet()
     proto.MergeFromString(serialized)
 
     # Verify that the unknown extension is serialized unchanged
@@ -100,13 +107,6 @@ class UnknownFieldsTest(unittest.TestCase):
     new_raw.MergeFromString(reserialized)
     self.assertEqual(raw, new_raw)
 
-  # C++ implementation for proto2 does not currently take into account unknown
-  # fields when checking equality.
-  #
-  # TODO(haberman): fix this.
-  @unittest.skipIf(
-      api_implementation.Type() == 'cpp' and api_implementation.Version() == 2,
-      'C++ implementation does not expose unknown fields to Python')
   def testEquals(self):
     message = unittest_pb2.TestEmptyMessage()
     message.ParseFromString(self.all_fields_data)
@@ -117,9 +117,6 @@ class UnknownFieldsTest(unittest.TestCase):
     self.assertNotEqual(self.empty_message, message)
 
 
-@unittest.skipIf(
-    api_implementation.Type() == 'cpp' and api_implementation.Version() == 2,
-    'C++ implementation does not expose unknown fields to Python')
 class UnknownFieldsAccessorsTest(unittest.TestCase):
 
   def setUp(self):
@@ -129,7 +126,14 @@ class UnknownFieldsAccessorsTest(unittest.TestCase):
     self.all_fields_data = self.all_fields.SerializeToString()
     self.empty_message = unittest_pb2.TestEmptyMessage()
     self.empty_message.ParseFromString(self.all_fields_data)
-    self.unknown_fields = self.empty_message._unknown_fields
+    if api_implementation.Type() != 'cpp':
+      # _unknown_fields is an implementation detail.
+      self.unknown_fields = self.empty_message._unknown_fields
+
+  # All the tests that use GetField() check an implementation detail of the
+  # Python implementation, which stores unknown fields as serialized strings.
+  # These tests are skipped by the C++ implementation: it's enough to check that
+  # the message is correctly serialized.
 
   def GetField(self, name):
     field_descriptor = self.descriptor.fields_by_name[name]
@@ -142,30 +146,37 @@ class UnknownFieldsAccessorsTest(unittest.TestCase):
         decoder(value, 0, len(value), self.all_fields, result_dict)
     return result_dict[field_descriptor]
 
+  @SkipIfCppImplementation
   def testEnum(self):
     value = self.GetField('optional_nested_enum')
     self.assertEqual(self.all_fields.optional_nested_enum, value)
 
+  @SkipIfCppImplementation
   def testRepeatedEnum(self):
     value = self.GetField('repeated_nested_enum')
     self.assertEqual(self.all_fields.repeated_nested_enum, value)
 
+  @SkipIfCppImplementation
   def testVarint(self):
     value = self.GetField('optional_int32')
     self.assertEqual(self.all_fields.optional_int32, value)
 
+  @SkipIfCppImplementation
   def testFixed32(self):
     value = self.GetField('optional_fixed32')
     self.assertEqual(self.all_fields.optional_fixed32, value)
 
+  @SkipIfCppImplementation
   def testFixed64(self):
     value = self.GetField('optional_fixed64')
     self.assertEqual(self.all_fields.optional_fixed64, value)
 
+  @SkipIfCppImplementation
   def testLengthDelimited(self):
     value = self.GetField('optional_string')
     self.assertEqual(self.all_fields.optional_string, value)
 
+  @SkipIfCppImplementation
   def testGroup(self):
     value = self.GetField('optionalgroup')
     self.assertEqual(self.all_fields.optionalgroup, value)
@@ -173,7 +184,7 @@ class UnknownFieldsAccessorsTest(unittest.TestCase):
   def testCopyFrom(self):
     message = unittest_pb2.TestEmptyMessage()
     message.CopyFrom(self.empty_message)
-    self.assertEqual(self.unknown_fields, message._unknown_fields)
+    self.assertEqual(message.SerializeToString(), self.all_fields_data)
 
   def testMergeFrom(self):
     message = unittest_pb2.TestAllTypes()
@@ -187,27 +198,26 @@ class UnknownFieldsAccessorsTest(unittest.TestCase):
     message.optional_uint32 = 4
     destination = unittest_pb2.TestEmptyMessage()
     destination.ParseFromString(message.SerializeToString())
-    unknown_fields = destination._unknown_fields[:]
 
     destination.MergeFrom(source)
-    self.assertEqual(unknown_fields + source._unknown_fields,
-                     destination._unknown_fields)
+    # Check that the fields where correctly merged, even stored in the unknown
+    # fields set.
+    message.ParseFromString(destination.SerializeToString())
+    self.assertEqual(message.optional_int32, 1)
+    self.assertEqual(message.optional_uint32, 2)
+    self.assertEqual(message.optional_int64, 3)
 
   def testClear(self):
     self.empty_message.Clear()
-    self.assertEqual(0, len(self.empty_message._unknown_fields))
+    # All cleared, even unknown fields.
+    self.assertEqual(self.empty_message.SerializeToString(), b'')
 
   def testUnknownExtensions(self):
     message = unittest_pb2.TestEmptyMessageWithExtensions()
     message.ParseFromString(self.all_fields_data)
-    self.assertEqual(self.empty_message._unknown_fields,
-                     message._unknown_fields)
-
+    self.assertEqual(message.SerializeToString(), self.all_fields_data)
 
 
-@unittest.skipIf(
-    api_implementation.Type() == 'cpp' and api_implementation.Version() == 2,
-    'C++ implementation does not expose unknown fields to Python')
 class UnknownEnumValuesTest(unittest.TestCase):
 
   def setUp(self):
@@ -227,7 +237,14 @@ class UnknownEnumValuesTest(unittest.TestCase):
     self.message_data = self.message.SerializeToString()
     self.missing_message = missing_enum_values_pb2.TestMissingEnumValues()
     self.missing_message.ParseFromString(self.message_data)
-    self.unknown_fields = self.missing_message._unknown_fields
+    if api_implementation.Type() != 'cpp':
+      # _unknown_fields is an implementation detail.
+      self.unknown_fields = self.missing_message._unknown_fields
+
+  # All the tests that use GetField() check an implementation detail of the
+  # Python implementation, which stores unknown fields as serialized strings.
+  # These tests are skipped by the C++ implementation: it's enough to check that
+  # the message is correctly serialized.
 
   def GetField(self, name):
     field_descriptor = self.descriptor.fields_by_name[name]
@@ -241,15 +258,18 @@ class UnknownEnumValuesTest(unittest.TestCase):
         decoder(value, 0, len(value), self.message, result_dict)
     return result_dict[field_descriptor]
 
+  @SkipIfCppImplementation
   def testUnknownEnumValue(self):
     self.assertFalse(self.missing_message.HasField('optional_nested_enum'))
     value = self.GetField('optional_nested_enum')
     self.assertEqual(self.message.optional_nested_enum, value)
 
+  @SkipIfCppImplementation
   def testUnknownRepeatedEnumValue(self):
     value = self.GetField('repeated_nested_enum')
     self.assertEqual(self.message.repeated_nested_enum, value)
 
+  @SkipIfCppImplementation
   def testUnknownPackedEnumValue(self):
     value = self.GetField('packed_nested_enum')
     self.assertEqual(self.message.packed_nested_enum, value)
diff --git a/python/google/protobuf/pyext/cpp_message.py b/python/google/protobuf/pyext/cpp_message.py
index 037bb72c..b215211e 100644
--- a/python/google/protobuf/pyext/cpp_message.py
+++ b/python/google/protobuf/pyext/cpp_message.py
@@ -37,21 +37,29 @@ Descriptor objects at runtime backed by the protocol buffer C++ API.
 __author__ = 'tibell@google.com (Johan Tibell)'
 
 from google.protobuf.pyext import _message
-from google.protobuf import message
 
 
-def NewMessage(bases, message_descriptor, dictionary):
-  """Creates a new protocol message *class*."""
-  new_bases = []
-  for base in bases:
-    if base is message.Message:
-      # _message.Message must come before message.Message as it
-      # overrides methods in that class.
-      new_bases.append(_message.Message)
-    new_bases.append(base)
-  return tuple(new_bases)
+class GeneratedProtocolMessageType(_message.MessageMeta):
 
+  """Metaclass for protocol message classes created at runtime from Descriptors.
 
-def InitMessage(message_descriptor, cls):
-  """Finalizes the creation of a message class."""
-  cls.AddDescriptors(message_descriptor)
+  The protocol compiler currently uses this metaclass to create protocol
+  message classes at runtime.  Clients can also manually create their own
+  classes at runtime, as in this example:
+
+  mydescriptor = Descriptor(.....)
+  class MyProtoClass(Message):
+    __metaclass__ = GeneratedProtocolMessageType
+    DESCRIPTOR = mydescriptor
+  myproto_instance = MyProtoClass()
+  myproto.foo_field = 23
+  ...
+
+  The above example will not work for nested types. If you wish to include them,
+  use reflection.MakeClass() instead of manually instantiating the class in
+  order to create the appropriate class structure.
+  """
+
+  # Must be consistent with the protocol-compiler code in
+  # proto2/compiler/internal/generator.*.
+  _DESCRIPTOR_KEY = 'DESCRIPTOR'
diff --git a/python/google/protobuf/pyext/descriptor.cc b/python/google/protobuf/pyext/descriptor.cc
index 2160757b..8581f529 100644
--- a/python/google/protobuf/pyext/descriptor.cc
+++ b/python/google/protobuf/pyext/descriptor.cc
@@ -193,7 +193,7 @@ static PyObject* GetOrBuildOptions(const DescriptorClass *descriptor) {
     io::CodedInputStream input(
         reinterpret_cast<const uint8*>(serialized.c_str()), serialized.size());
     input.SetExtensionRegistry(GetDescriptorPool()->pool,
-                               cmessage::GetMessageFactory());
+                               GetDescriptorPool()->message_factory);
     bool success = cmsg->message->MergePartialFromCodedStream(&input);
     if (!success) {
       PyErr_Format(PyExc_ValueError, "Error parsing Options message");
diff --git a/python/google/protobuf/pyext/descriptor_pool.cc b/python/google/protobuf/pyext/descriptor_pool.cc
index ecd90847..d5ba2b6f 100644
--- a/python/google/protobuf/pyext/descriptor_pool.cc
+++ b/python/google/protobuf/pyext/descriptor_pool.cc
@@ -33,6 +33,7 @@
 #include <Python.h>
 
 #include <google/protobuf/descriptor.pb.h>
+#include <google/protobuf/dynamic_message.h>
 #include <google/protobuf/pyext/descriptor_pool.h>
 #include <google/protobuf/pyext/descriptor.h>
 #include <google/protobuf/pyext/message.h>
@@ -67,6 +68,11 @@ PyDescriptorPool* NewDescriptorPool() {
   // as underlay.
   cdescriptor_pool->pool = new DescriptorPool(DescriptorPool::generated_pool());
 
+  DynamicMessageFactory* message_factory = new DynamicMessageFactory();
+  // This option might be the default some day.
+  message_factory->SetDelegateToGeneratedFactory(true);
+  cdescriptor_pool->message_factory = message_factory;
+
   // TODO(amauryfa): Rewrite the SymbolDatabase in C so that it uses the same
   // storage.
   cdescriptor_pool->classes_by_descriptor =
@@ -93,6 +99,7 @@ static void Dealloc(PyDescriptorPool* self) {
     Py_DECREF(it->second);
   }
   delete self->descriptor_options;
+  delete self->message_factory;
   Py_TYPE(self)->tp_free(reinterpret_cast<PyObject*>(self));
 }
 
diff --git a/python/google/protobuf/pyext/descriptor_pool.h b/python/google/protobuf/pyext/descriptor_pool.h
index efb1abeb..6f6c5cdb 100644
--- a/python/google/protobuf/pyext/descriptor_pool.h
+++ b/python/google/protobuf/pyext/descriptor_pool.h
@@ -38,6 +38,8 @@
 
 namespace google {
 namespace protobuf {
+class MessageFactory;
+
 namespace python {
 
 // Wraps operations to the global DescriptorPool which contains information
@@ -55,6 +57,14 @@ typedef struct PyDescriptorPool {
 
   DescriptorPool* pool;
 
+  // DynamicMessageFactory used to create C++ instances of messages.
+  // This object cache the descriptors that were used, so the DescriptorPool
+  // needs to get rid of it before it can delete itself.
+  //
+  // Note: A C++ MessageFactory is different from the Python MessageFactory.
+  // The C++ one creates messages, when the Python one creates classes.
+  MessageFactory* message_factory;
+
   // Make our own mapping to retrieve Python classes from C++ descriptors.
   //
   // Descriptor pointers stored here are owned by the DescriptorPool above.
diff --git a/python/google/protobuf/pyext/extension_dict.cc b/python/google/protobuf/pyext/extension_dict.cc
index b8d18f8d..8ebbb27c 100644
--- a/python/google/protobuf/pyext/extension_dict.cc
+++ b/python/google/protobuf/pyext/extension_dict.cc
@@ -33,6 +33,7 @@
 
 #include <google/protobuf/pyext/extension_dict.h>
 
+#include <google/protobuf/stubs/logging.h>
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/dynamic_message.h>
@@ -183,7 +184,8 @@ PyObject* ClearExtension(ExtensionDict* self, PyObject* extension) {
       return NULL;
     }
   }
-  if (cmessage::ClearFieldByDescriptor(self->parent, descriptor) == NULL) {
+  if (ScopedPyObjectPtr(cmessage::ClearFieldByDescriptor(
+          self->parent, descriptor)) == NULL) {
     return NULL;
   }
   if (PyDict_DelItem(self->values, extension) < 0) {
@@ -268,7 +270,7 @@ PyTypeObject ExtensionDict_Type = {
   0,                                   //  tp_as_number
   0,                                   //  tp_as_sequence
   &extension_dict::MpMethods,          //  tp_as_mapping
-  0,                                   //  tp_hash
+  PyObject_HashNotImplemented,         //  tp_hash
   0,                                   //  tp_call
   0,                                   //  tp_str
   0,                                   //  tp_getattro
diff --git a/python/google/protobuf/pyext/message.cc b/python/google/protobuf/pyext/message.cc
index a4843e8d..aa3ab97a 100644
--- a/python/google/protobuf/pyext/message.cc
+++ b/python/google/protobuf/pyext/message.cc
@@ -49,9 +49,10 @@
 #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/util/message_differencer.h>
 #include <google/protobuf/descriptor.h>
-#include <google/protobuf/dynamic_message.h>
 #include <google/protobuf/message.h>
 #include <google/protobuf/text_format.h>
 #include <google/protobuf/pyext/descriptor.h>
@@ -88,12 +89,308 @@ namespace google {
 namespace protobuf {
 namespace python {
 
+static PyObject* kDESCRIPTOR;
+static PyObject* k_extensions_by_name;
+static PyObject* k_extensions_by_number;
+PyObject* EnumTypeWrapper_class;
+static PyObject* PythonMessage_class;
+static PyObject* kEmptyWeakref;
+
+// Defines the Metaclass of all Message 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.
+
+struct PyMessageMeta {
+  // This is how CPython subclasses C structures: the base structure must be
+  // the first member of the object.
+  PyHeapTypeObject super;
+
+  // C++ descriptor of this message.
+  const Descriptor* message_descriptor;
+  // Owned reference, used to keep the pointer above alive.
+  PyObject* py_message_descriptor;
+};
+
+namespace message_meta {
+
+static int InsertEmptyWeakref(PyTypeObject* base);
+
+// 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, number) == -1) {
+    return false;
+  }
+  return true;
+}
+
+
+// Finalize the creation of the Message class.
+// Called from its metaclass: GeneratedProtocolMessageType.__init__().
+static int AddDescriptors(PyObject* cls, PyObject* descriptor) {
+  const Descriptor* message_descriptor =
+      cdescriptor_pool::RegisterMessageClass(
+          GetDescriptorPool(), cls, descriptor);
+  if (message_descriptor == NULL) {
+    return -1;
+  }
+
+  // If there are extension_ranges, the message is "extendable", and extension
+  // classes will register themselves in this class.
+  if (message_descriptor->extension_range_count() > 0) {
+    ScopedPyObjectPtr by_name(PyDict_New());
+    if (PyObject_SetAttr(cls, k_extensions_by_name, by_name) < 0) {
+      return -1;
+    }
+    ScopedPyObjectPtr by_number(PyDict_New());
+    if (PyObject_SetAttr(cls, k_extensions_by_number, by_number) < 0) {
+      return -1;
+    }
+  }
+
+  // For each field set: cls.<field>_FIELD_NUMBER = <number>
+  for (int i = 0; i < message_descriptor->field_count(); ++i) {
+    if (!AddFieldNumberToClass(cls, message_descriptor->field(i))) {
+      return -1;
+    }
+  }
+
+  // For each enum set cls.<enum name> = EnumTypeWrapper(<enum descriptor>).
+  //
+  // The enum descriptor we get from
+  // <messagedescriptor>.enum_types_by_name[name]
+  // which was built previously.
+  for (int i = 0; i < message_descriptor->enum_type_count(); ++i) {
+    const EnumDescriptor* enum_descriptor = message_descriptor->enum_type(i);
+    ScopedPyObjectPtr enum_type(
+        PyEnumDescriptor_FromDescriptor(enum_descriptor));
+    if (enum_type == NULL) {
+      return -1;
+     }
+    // Add wrapped enum type to message class.
+    ScopedPyObjectPtr wrapped(PyObject_CallFunctionObjArgs(
+        EnumTypeWrapper_class, enum_type.get(), NULL));
+    if (wrapped == NULL) {
+      return -1;
+    }
+    if (PyObject_SetAttrString(
+            cls, enum_descriptor->name().c_str(), wrapped) == -1) {
+      return -1;
+    }
+
+    // For each enum value add cls.<name> = <number>
+    for (int j = 0; j < enum_descriptor->value_count(); ++j) {
+      const EnumValueDescriptor* enum_value_descriptor =
+          enum_descriptor->value(j);
+      ScopedPyObjectPtr value_number(PyInt_FromLong(
+          enum_value_descriptor->number()));
+      if (value_number == NULL) {
+        return -1;
+      }
+      if (PyObject_SetAttrString(
+              cls, enum_value_descriptor->name().c_str(), value_number) == -1) {
+        return -1;
+      }
+    }
+  }
+
+  // For each extension set cls.<extension name> = <extension descriptor>.
+  //
+  // Extension descriptors come from
+  // <message descriptor>.extensions_by_name[name]
+  // which was defined previously.
+  for (int i = 0; i < message_descriptor->extension_count(); ++i) {
+    const google::protobuf::FieldDescriptor* field = message_descriptor->extension(i);
+    ScopedPyObjectPtr extension_field(PyFieldDescriptor_FromDescriptor(field));
+    if (extension_field == NULL) {
+      return -1;
+    }
+
+    // Add the extension field to the message class.
+    if (PyObject_SetAttrString(
+            cls, field->name().c_str(), extension_field) == -1) {
+      return -1;
+    }
+
+    // For each extension set cls.<extension name>_FIELD_NUMBER = <number>.
+    if (!AddFieldNumberToClass(cls, field)) {
+      return -1;
+    }
+  }
+
+  return 0;
+}
+
+static PyObject* New(PyTypeObject* type,
+                     PyObject* args, PyObject* kwargs) {
+  static char *kwlist[] = {"name", "bases", "dict", 0};
+  PyObject *bases, *dict;
+  const char* name;
+
+  // Check arguments: (name, bases, dict)
+  if (!PyArg_ParseTupleAndKeywords(args, kwargs, "sO!O!:type", kwlist,
+                                   &name,
+                                   &PyTuple_Type, &bases,
+                                   &PyDict_Type, &dict)) {
+    return NULL;
+  }
+
+  // Check bases: only (), or (message.Message,) are allowed
+  if (!(PyTuple_GET_SIZE(bases) == 0 ||
+        (PyTuple_GET_SIZE(bases) == 1 &&
+         PyTuple_GET_ITEM(bases, 0) == PythonMessage_class))) {
+    PyErr_SetString(PyExc_TypeError,
+                    "A Message class can only inherit from Message");
+    return NULL;
+  }
+
+  // Check dict['DESCRIPTOR']
+  PyObject* descriptor = PyDict_GetItem(dict, kDESCRIPTOR);
+  if (descriptor == NULL) {
+    PyErr_SetString(PyExc_TypeError, "Message class has no DESCRIPTOR");
+    return NULL;
+  }
+  if (!PyObject_TypeCheck(descriptor, &PyMessageDescriptor_Type)) {
+    PyErr_Format(PyExc_TypeError, "Expected a message Descriptor, got %s",
+                 descriptor->ob_type->tp_name);
+    return NULL;
+  }
+
+  // Build the arguments to the base metaclass.
+  // We change the __bases__ classes.
+  ScopedPyObjectPtr new_args(Py_BuildValue(
+      "s(OO)O", name, &CMessage_Type, PythonMessage_class, dict));
+  if (new_args == NULL) {
+    return NULL;
+  }
+  // Call the base metaclass.
+  ScopedPyObjectPtr result(PyType_Type.tp_new(type, new_args, NULL));
+  if (result == NULL) {
+    return NULL;
+  }
+  PyMessageMeta* newtype = reinterpret_cast<PyMessageMeta*>(result.get());
+
+  // Insert the empty weakref into the base classes.
+  if (InsertEmptyWeakref(
+          reinterpret_cast<PyTypeObject*>(PythonMessage_class)) < 0 ||
+      InsertEmptyWeakref(&CMessage_Type) < 0) {
+    return NULL;
+  }
+
+  // Cache the descriptor, both as Python object and as C++ pointer.
+  const Descriptor* message_descriptor =
+      PyMessageDescriptor_AsDescriptor(descriptor);
+  if (message_descriptor == NULL) {
+    return NULL;
+  }
+  Py_INCREF(descriptor);
+  newtype->py_message_descriptor = descriptor;
+  newtype->message_descriptor = message_descriptor;
+
+  // Continue with type initialization: add other descriptors, enum values...
+  if (AddDescriptors(result, descriptor) < 0) {
+    return NULL;
+  }
+  return result.release();
+}
+
+static void Dealloc(PyMessageMeta *self) {
+  Py_DECREF(self->py_message_descriptor);
+  Py_TYPE(self)->tp_free(reinterpret_cast<PyObject*>(self));
+}
+
+static PyObject* GetDescriptor(PyMessageMeta *self, void *closure) {
+  Py_INCREF(self->py_message_descriptor);
+  return self->py_message_descriptor;
+}
+
+
+// This function inserts and empty weakref at the end of the list of
+// subclasses for the main protocol buffer Message class.
+//
+// This eliminates a O(n^2) behaviour in the internal add_subclass
+// routine.
+static int InsertEmptyWeakref(PyTypeObject *base_type) {
+#if PY_MAJOR_VERSION >= 3
+  // Python 3.4 has already included the fix for the issue that this
+  // hack addresses. For further background and the fix please see
+  // https://bugs.python.org/issue17936.
+  return 0;
+#else
+  PyObject *subclasses = base_type->tp_subclasses;
+  if (subclasses && PyList_CheckExact(subclasses)) {
+    return PyList_Append(subclasses, kEmptyWeakref);
+  }
+  return 0;
+#endif  // PY_MAJOR_VERSION >= 3
+}
+
+}  // namespace message_meta
+
+PyTypeObject PyMessageMeta_Type {
+  PyVarObject_HEAD_INIT(&PyType_Type, 0)
+  FULL_MODULE_NAME ".MessageMeta",     // tp_name
+  sizeof(PyMessageMeta),               // tp_basicsize
+  0,                                   // tp_itemsize
+  (destructor)message_meta::Dealloc,   // tp_dealloc
+  0,                                   // tp_print
+  0,                                   // tp_getattr
+  0,                                   // tp_setattr
+  0,                                   // tp_compare
+  0,                                   // tp_repr
+  0,                                   // tp_as_number
+  0,                                   // tp_as_sequence
+  0,                                   // tp_as_mapping
+  0,                                   // tp_hash
+  0,                                   // tp_call
+  0,                                   // tp_str
+  0,                                   // tp_getattro
+  0,                                   // tp_setattro
+  0,                                   // tp_as_buffer
+  Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  // tp_flags
+  "The metaclass of ProtocolMessages",  // tp_doc
+  0,                                   // tp_traverse
+  0,                                   // tp_clear
+  0,                                   // tp_richcompare
+  0,                                   // tp_weaklistoffset
+  0,                                   // tp_iter
+  0,                                   // tp_iternext
+  0,                                   // tp_methods
+  0,                                   // tp_members
+  0,                                   // tp_getset
+  0,                                   // tp_base
+  0,                                   // tp_dict
+  0,                                   // tp_descr_get
+  0,                                   // tp_descr_set
+  0,                                   // tp_dictoffset
+  0,                                   // tp_init
+  0,                                   // tp_alloc
+  message_meta::New,                   // tp_new
+};
+
+static const Descriptor* GetMessageDescriptor(PyTypeObject* cls) {
+  if (!PyObject_TypeCheck(cls, &PyMessageMeta_Type)) {
+    PyErr_Format(PyExc_TypeError, "Class %s is not a Message", cls->tp_name);
+    return NULL;
+  }
+  return reinterpret_cast<PyMessageMeta*>(cls)->message_descriptor;
+}
+
 // Forward declarations
 namespace cmessage {
-static const FieldDescriptor* GetFieldDescriptor(
-    CMessage* self, PyObject* name);
-static const Descriptor* GetMessageDescriptor(PyTypeObject* cls);
-static string GetMessageName(CMessage* self);
 int InternalReleaseFieldByDescriptor(
     CMessage* self,
     const FieldDescriptor* field_descriptor,
@@ -180,7 +477,7 @@ int ForEachCompositeField(CMessage* self, Visitor visitor) {
   if (self->composite_fields) {
     // Never use self->message in this function, it may be already freed.
     const Descriptor* message_descriptor =
-        cmessage::GetMessageDescriptor(Py_TYPE(self));
+        GetMessageDescriptor(Py_TYPE(self));
     while (PyDict_Next(self->composite_fields, &pos, &key, &field)) {
       Py_ssize_t key_str_size;
       char *key_str_data;
@@ -213,8 +510,6 @@ int ForEachCompositeField(CMessage* self, Visitor visitor) {
 
 // ---------------------------------------------------------------------
 
-static DynamicMessageFactory* message_factory;
-
 // Constants used for integer type range checking.
 PyObject* kPythonZero;
 PyObject* kint32min_py;
@@ -224,17 +519,13 @@ PyObject* kint64min_py;
 PyObject* kint64max_py;
 PyObject* kuint64max_py;
 
-PyObject* EnumTypeWrapper_class;
 PyObject* EncodeError_class;
 PyObject* DecodeError_class;
 PyObject* PickleError_class;
 
 // Constant PyString values used for GetAttr/GetItem.
-static PyObject* kDESCRIPTOR;
 static PyObject* k_cdescriptor;
 static PyObject* kfull_name;
-static PyObject* k_extensions_by_name;
-static PyObject* k_extensions_by_number;
 
 /* Is 64bit */
 void FormatTypeError(PyObject* arg, char* expected_types) {
@@ -432,10 +723,6 @@ bool CheckFieldBelongsToMessage(const FieldDescriptor* field_descriptor,
 
 namespace cmessage {
 
-DynamicMessageFactory* GetMessageFactory() {
-  return message_factory;
-}
-
 static int MaybeReleaseOverlappingOneofField(
     CMessage* cmessage,
     const FieldDescriptor* field) {
@@ -486,7 +773,7 @@ static Message* GetMutableMessage(
     return NULL;
   }
   return reflection->MutableMessage(
-      parent_message, parent_field, message_factory);
+      parent_message, parent_field, GetDescriptorPool()->message_factory);
 }
 
 struct FixupMessageReference : public ChildVisitor {
@@ -527,8 +814,9 @@ int AssureWritable(CMessage* self) {
     // If parent is NULL but we are trying to modify a read-only message, this
     // is a reference to a constant default instance that needs to be replaced
     // with a mutable top-level message.
-    const Message* prototype = message_factory->GetPrototype(
-        self->message->GetDescriptor());
+    const Message* prototype =
+        GetDescriptorPool()->message_factory->GetPrototype(
+            self->message->GetDescriptor());
     self->message = prototype->New();
     self->owner.reset(self->message);
     // Cascade the new owner to eventual children: even if this message is
@@ -567,23 +855,6 @@ int AssureWritable(CMessage* self) {
 
 // --- Globals:
 
-// Retrieve the C++ Descriptor of a message class.
-// On error, returns NULL with an exception set.
-static const Descriptor* GetMessageDescriptor(PyTypeObject* cls) {
-  ScopedPyObjectPtr descriptor(PyObject_GetAttr(
-      reinterpret_cast<PyObject*>(cls), kDESCRIPTOR));
-  if (descriptor == NULL) {
-    PyErr_SetString(PyExc_TypeError, "Message class has no DESCRIPTOR");
-    return NULL;
-  }
-  if (!PyObject_TypeCheck(descriptor, &PyMessageDescriptor_Type)) {
-    PyErr_Format(PyExc_TypeError, "Expected a message Descriptor, got %s",
-                 descriptor->ob_type->tp_name);
-    return NULL;
-  }
-  return PyMessageDescriptor_AsDescriptor(descriptor);
-}
-
 // Retrieve a C++ FieldDescriptor for a message attribute.
 // The C++ message must be valid.
 // TODO(amauryfa): This function should stay internal, because exception
@@ -846,9 +1117,9 @@ int InitAttributes(CMessage* self, PyObject* kwargs) {
           return -1;
         }
       } else {
-        if (repeated_scalar_container::Extend(
+        if (ScopedPyObjectPtr(repeated_scalar_container::Extend(
                 reinterpret_cast<RepeatedScalarContainer*>(container.get()),
-                value) ==
+                value)) ==
             NULL) {
           return -1;
         }
@@ -927,7 +1198,7 @@ static PyObject* New(PyTypeObject* type,
     return NULL;
   }
   const Message* default_message =
-      message_factory->GetPrototype(message_descriptor);
+      GetDescriptorPool()->message_factory->GetPrototype(message_descriptor);
   if (default_message == NULL) {
     PyErr_SetString(PyExc_TypeError, message_descriptor->full_name().c_str());
     return NULL;
@@ -1257,6 +1528,7 @@ int SetOwner(CMessage* self, const shared_ptr<Message>& new_owner) {
 Message* ReleaseMessage(CMessage* self,
                         const Descriptor* descriptor,
                         const FieldDescriptor* field_descriptor) {
+  MessageFactory* message_factory = GetDescriptorPool()->message_factory;
   Message* released_message = self->message->GetReflection()->ReleaseMessage(
       self->message, field_descriptor, message_factory);
   // ReleaseMessage will return NULL which differs from
@@ -1492,34 +1764,35 @@ static PyObject* SerializePartialToString(CMessage* self) {
 // appropriate.
 class PythonFieldValuePrinter : public TextFormat::FieldValuePrinter {
  public:
-  PythonFieldValuePrinter() : float_holder_(PyFloat_FromDouble(0)) {}
-
   // Python has some differences from C++ when printing floating point numbers.
   //
   // 1) Trailing .0 is always printed.
-  // 2) Outputted is rounded to 12 digits.
+  // 2) (Python2) Output is rounded to 12 digits.
+  // 3) (Python3) The full precision of the double is preserved (and Python uses
+  //    David M. Gay's dtoa(), when the C++ code uses SimpleDtoa. There are some
+  //    differences, but they rarely happen)
   //
   // We override floating point printing with the C-API function for printing
   // Python floats to ensure consistency.
   string PrintFloat(float value) const { return PrintDouble(value); }
   string PrintDouble(double value) const {
-    reinterpret_cast<PyFloatObject*>(float_holder_.get())->ob_fval = value;
-    ScopedPyObjectPtr s(PyObject_Str(float_holder_.get()));
-    if (s == NULL) return string();
+    // Same as float.__str__()
+    char* buf = PyOS_double_to_string(
+        value,
 #if PY_MAJOR_VERSION < 3
-    char *cstr = PyBytes_AS_STRING(static_cast<PyObject*>(s));
+        'g', PyFloat_STR_PRECISION,  // Output is rounded to 12 digits.
 #else
-    char *cstr = PyUnicode_AsUTF8(s);
+        'r', 0,
 #endif
-    return string(cstr);
+        Py_DTSF_ADD_DOT_0,  // Trailing .0 is always printed.
+        NULL);
+    if (!buf) {
+      return string();
+    }
+    string result(buf);
+    PyMem_Free(buf);
+    return result;
   }
-
- private:
-  // Holder for a python float object which we use to allow us to use
-  // the Python API for printing doubles. We initialize once and then
-  // directly modify it for every float printed to save on allocations
-  // and refcounting.
-  ScopedPyObjectPtr float_holder_;
 };
 
 static PyObject* ToStr(CMessage* self) {
@@ -1590,7 +1863,7 @@ static PyObject* CopyFrom(CMessage* self, PyObject* arg) {
 
   // CopyFrom on the message will not clean up self->composite_fields,
   // which can leave us in an inconsistent state, so clear it out here.
-  Clear(self);
+  (void)ScopedPyObjectPtr(Clear(self));
 
   self->message->CopyFrom(*other_message->message);
 
@@ -1607,7 +1880,8 @@ static PyObject* MergeFromString(CMessage* self, PyObject* arg) {
   AssureWritable(self);
   io::CodedInputStream input(
       reinterpret_cast<const uint8*>(data), data_length);
-  input.SetExtensionRegistry(GetDescriptorPool()->pool, message_factory);
+  input.SetExtensionRegistry(GetDescriptorPool()->pool,
+                             GetDescriptorPool()->message_factory);
   bool success = self->message->MergePartialFromCodedStream(&input);
   if (success) {
     return PyInt_FromLong(input.CurrentPosition());
@@ -1618,7 +1892,7 @@ static PyObject* MergeFromString(CMessage* self, PyObject* arg) {
 }
 
 static PyObject* ParseFromString(CMessage* self, PyObject* arg) {
-  if (Clear(self) == NULL) {
+  if (ScopedPyObjectPtr(Clear(self)) == NULL) {
     return NULL;
   }
   return MergeFromString(self, arg);
@@ -1790,6 +2064,7 @@ static PyObject* ListFields(CMessage* self) {
       // Steals reference to 'extension'
       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()));
@@ -1841,28 +2116,34 @@ PyObject* FindInitializationErrors(CMessage* self) {
 }
 
 static PyObject* RichCompare(CMessage* self, PyObject* other, int opid) {
-  if (!PyObject_TypeCheck(other, &CMessage_Type)) {
-    if (opid == Py_EQ) {
-      Py_RETURN_FALSE;
-    } else if (opid == Py_NE) {
-      Py_RETURN_TRUE;
-    }
-  }
-  if (opid == Py_EQ || opid == Py_NE) {
-    ScopedPyObjectPtr self_fields(ListFields(self));
-    if (!self_fields) {
-      return NULL;
-    }
-    ScopedPyObjectPtr other_fields(ListFields(
-        reinterpret_cast<CMessage*>(other)));
-    if (!other_fields) {
-      return NULL;
-    }
-    return PyObject_RichCompare(self_fields, other_fields, opid);
-  } else {
+  // Only equality comparisons are implemented.
+  if (opid != Py_EQ && opid != Py_NE) {
     Py_INCREF(Py_NotImplemented);
     return Py_NotImplemented;
   }
+  bool equals = true;
+  // If other is not a message, it cannot be equal.
+  if (!PyObject_TypeCheck(other, &CMessage_Type)) {
+    equals = false;
+  }
+  const google::protobuf::Message* other_message =
+      reinterpret_cast<CMessage*>(other)->message;
+  // If messages don't have the same descriptors, they are not equal.
+  if (equals &&
+      self->message->GetDescriptor() != other_message->GetDescriptor()) {
+    equals = false;
+  }
+  // Check the message contents.
+  if (equals && !google::protobuf::util::MessageDifferencer::Equals(
+          *self->message,
+          *reinterpret_cast<CMessage*>(other)->message)) {
+    equals = false;
+  }
+  if (equals ^ (opid == Py_EQ)) {
+    Py_RETURN_FALSE;
+  } else {
+    Py_RETURN_TRUE;
+  }
 }
 
 PyObject* InternalGetScalar(const Message* message,
@@ -1950,7 +2231,7 @@ PyObject* InternalGetSubMessage(
     CMessage* self, const FieldDescriptor* field_descriptor) {
   const Reflection* reflection = self->message->GetReflection();
   const Message& sub_message = reflection->GetMessage(
-      *self->message, field_descriptor, message_factory);
+      *self->message, field_descriptor, GetDescriptorPool()->message_factory);
 
   PyObject *message_class = cdescriptor_pool::GetMessageClass(
       GetDescriptorPool(), field_descriptor->message_type());
@@ -2085,125 +2366,6 @@ PyObject* FromString(PyTypeObject* cls, PyObject* serialized) {
   return py_cmsg;
 }
 
-// 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, number) == -1) {
-    return false;
-  }
-  return true;
-}
-
-
-// Finalize the creation of the Message class.
-// Called from its metaclass: GeneratedProtocolMessageType.__init__().
-static PyObject* AddDescriptors(PyObject* cls, PyObject* descriptor) {
-  const Descriptor* message_descriptor =
-      cdescriptor_pool::RegisterMessageClass(
-          GetDescriptorPool(), cls, descriptor);
-  if (message_descriptor == NULL) {
-    return NULL;
-  }
-
-  // If there are extension_ranges, the message is "extendable", and extension
-  // classes will register themselves in this class.
-  if (message_descriptor->extension_range_count() > 0) {
-    ScopedPyObjectPtr by_name(PyDict_New());
-    if (PyObject_SetAttr(cls, k_extensions_by_name, by_name) < 0) {
-      return NULL;
-    }
-    ScopedPyObjectPtr by_number(PyDict_New());
-    if (PyObject_SetAttr(cls, k_extensions_by_number, by_number) < 0) {
-      return NULL;
-    }
-  }
-
-  // For each field set: cls.<field>_FIELD_NUMBER = <number>
-  for (int i = 0; i < message_descriptor->field_count(); ++i) {
-    if (!AddFieldNumberToClass(cls, message_descriptor->field(i))) {
-      return NULL;
-    }
-  }
-
-  // For each enum set cls.<enum name> = EnumTypeWrapper(<enum descriptor>).
-  //
-  // The enum descriptor we get from
-  // <messagedescriptor>.enum_types_by_name[name]
-  // which was built previously.
-  for (int i = 0; i < message_descriptor->enum_type_count(); ++i) {
-    const EnumDescriptor* enum_descriptor = message_descriptor->enum_type(i);
-    ScopedPyObjectPtr enum_type(
-        PyEnumDescriptor_FromDescriptor(enum_descriptor));
-    if (enum_type == NULL) {
-      return NULL;
-     }
-    // Add wrapped enum type to message class.
-    ScopedPyObjectPtr wrapped(PyObject_CallFunctionObjArgs(
-        EnumTypeWrapper_class, enum_type.get(), NULL));
-    if (wrapped == NULL) {
-      return NULL;
-    }
-    if (PyObject_SetAttrString(
-            cls, enum_descriptor->name().c_str(), wrapped) == -1) {
-      return NULL;
-    }
-
-    // For each enum value add cls.<name> = <number>
-    for (int j = 0; j < enum_descriptor->value_count(); ++j) {
-      const EnumValueDescriptor* enum_value_descriptor =
-          enum_descriptor->value(j);
-      ScopedPyObjectPtr value_number(PyInt_FromLong(
-          enum_value_descriptor->number()));
-      if (value_number == NULL) {
-        return NULL;
-      }
-      if (PyObject_SetAttrString(
-              cls, enum_value_descriptor->name().c_str(), value_number) == -1) {
-        return NULL;
-      }
-    }
-  }
-
-  // For each extension set cls.<extension name> = <extension descriptor>.
-  //
-  // Extension descriptors come from
-  // <message descriptor>.extensions_by_name[name]
-  // which was defined previously.
-  for (int i = 0; i < message_descriptor->extension_count(); ++i) {
-    const google::protobuf::FieldDescriptor* field = message_descriptor->extension(i);
-    ScopedPyObjectPtr extension_field(PyFieldDescriptor_FromDescriptor(field));
-    if (extension_field == NULL) {
-      return NULL;
-    }
-
-    // Add the extension field to the message class.
-    if (PyObject_SetAttrString(
-            cls, field->name().c_str(), extension_field) == -1) {
-      return NULL;
-    }
-
-    // For each extension set cls.<extension name>_FIELD_NUMBER = <number>.
-    if (!AddFieldNumberToClass(cls, field)) {
-      return NULL;
-    }
-  }
-
-  Py_RETURN_NONE;
-}
-
 PyObject* DeepCopy(CMessage* self, PyObject* arg) {
   PyObject* clone = PyObject_CallObject(
       reinterpret_cast<PyObject*>(Py_TYPE(self)), NULL);
@@ -2214,8 +2376,9 @@ PyObject* DeepCopy(CMessage* self, PyObject* arg) {
     Py_DECREF(clone);
     return NULL;
   }
-  if (MergeFrom(reinterpret_cast<CMessage*>(clone),
-                reinterpret_cast<PyObject*>(self)) == NULL) {
+  if (ScopedPyObjectPtr(MergeFrom(
+          reinterpret_cast<CMessage*>(clone),
+          reinterpret_cast<PyObject*>(self))) == NULL) {
     Py_DECREF(clone);
     return NULL;
   }
@@ -2281,7 +2444,7 @@ PyObject* SetState(CMessage* self, PyObject* state) {
   if (serialized == NULL) {
     return NULL;
   }
-  if (ParseFromString(self, serialized) == NULL) {
+  if (ScopedPyObjectPtr(ParseFromString(self, serialized)) == NULL) {
     return NULL;
   }
   Py_RETURN_NONE;
@@ -2314,8 +2477,6 @@ static PyMethodDef Methods[] = {
     "Inputs picklable representation of the message." },
   { "__unicode__", (PyCFunction)ToUnicode, METH_NOARGS,
     "Outputs a unicode representation of the message." },
-  { "AddDescriptors", (PyCFunction)AddDescriptors, METH_O | METH_CLASS,
-    "Adds field descriptors to the class" },
   { "ByteSize", (PyCFunction)ByteSize, METH_NOARGS,
     "Returns the size of the message in bytes." },
   { "Clear", (PyCFunction)Clear, METH_NOARGS,
@@ -2441,6 +2602,9 @@ PyObject* GetAttr(CMessage* self, PyObject* name) {
 
   if (field_descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
     PyObject* sub_message = InternalGetSubMessage(self, field_descriptor);
+    if (sub_message == NULL) {
+      return NULL;
+    }
     if (!SetCompositeField(self, name, sub_message)) {
       Py_DECREF(sub_message);
       return NULL;
@@ -2484,7 +2648,7 @@ int SetAttr(CMessage* self, PyObject* name, PyObject* value) {
 }  // namespace cmessage
 
 PyTypeObject CMessage_Type = {
-  PyVarObject_HEAD_INIT(&PyType_Type, 0)
+  PyVarObject_HEAD_INIT(&PyMessageMeta_Type, 0)
   FULL_MODULE_NAME ".CMessage",        // tp_name
   sizeof(CMessage),                    // tp_basicsize
   0,                                   //  tp_itemsize
@@ -2497,7 +2661,7 @@ PyTypeObject CMessage_Type = {
   0,                                   //  tp_as_number
   0,                                   //  tp_as_sequence
   0,                                   //  tp_as_mapping
-  0,                                   //  tp_hash
+  PyObject_HashNotImplemented,         //  tp_hash
   0,                                   //  tp_call
   (reprfunc)cmessage::ToStr,           //  tp_str
   (getattrofunc)cmessage::GetAttr,     //  tp_getattro
@@ -2580,8 +2744,9 @@ void InitGlobals() {
   k_extensions_by_name = PyString_FromString("_extensions_by_name");
   k_extensions_by_number = PyString_FromString("_extensions_by_number");
 
-  message_factory = new DynamicMessageFactory();
-  message_factory->SetDelegateToGeneratedFactory(true);
+  PyObject *dummy_obj = PySet_New(NULL);
+  kEmptyWeakref = PyWeakref_NewRef(dummy_obj, NULL);
+  Py_DECREF(dummy_obj);
 }
 
 bool InitProto2MessageModule(PyObject *m) {
@@ -2598,7 +2763,13 @@ bool InitProto2MessageModule(PyObject *m) {
   // Initialize constants defined in this file.
   InitGlobals();
 
-  CMessage_Type.tp_hash = PyObject_HashNotImplemented;
+  PyMessageMeta_Type.tp_base = &PyType_Type;
+  if (PyType_Ready(&PyMessageMeta_Type) < 0) {
+    return false;
+  }
+  PyModule_AddObject(m, "MessageMeta",
+                     reinterpret_cast<PyObject*>(&PyMessageMeta_Type));
+
   if (PyType_Ready(&CMessage_Type) < 0) {
     return false;
   }
@@ -2628,86 +2799,106 @@ bool InitProto2MessageModule(PyObject *m) {
 
   PyModule_AddObject(m, "Message", reinterpret_cast<PyObject*>(&CMessage_Type));
 
-  RepeatedScalarContainer_Type.tp_hash =
-      PyObject_HashNotImplemented;
-  if (PyType_Ready(&RepeatedScalarContainer_Type) < 0) {
-    return false;
-  }
+  // Initialize Repeated container types.
+  {
+    if (PyType_Ready(&RepeatedScalarContainer_Type) < 0) {
+      return false;
+    }
 
-  PyModule_AddObject(m, "RepeatedScalarContainer",
-                     reinterpret_cast<PyObject*>(
-                         &RepeatedScalarContainer_Type));
+    PyModule_AddObject(m, "RepeatedScalarContainer",
+                       reinterpret_cast<PyObject*>(
+                           &RepeatedScalarContainer_Type));
 
-  RepeatedCompositeContainer_Type.tp_hash = PyObject_HashNotImplemented;
-  if (PyType_Ready(&RepeatedCompositeContainer_Type) < 0) {
-    return false;
-  }
+    if (PyType_Ready(&RepeatedCompositeContainer_Type) < 0) {
+      return false;
+    }
 
-  PyModule_AddObject(
-      m, "RepeatedCompositeContainer",
-      reinterpret_cast<PyObject*>(
-          &RepeatedCompositeContainer_Type));
-
-  // ScalarMapContainer_Type derives from our MutableMapping type.
-  PyObject* containers =
-      PyImport_ImportModule("google.protobuf.internal.containers");
-  if (containers == NULL) {
-    return false;
+    PyModule_AddObject(
+        m, "RepeatedCompositeContainer",
+        reinterpret_cast<PyObject*>(
+            &RepeatedCompositeContainer_Type));
+
+    // Register them as collections.Sequence
+    ScopedPyObjectPtr collections(PyImport_ImportModule("collections"));
+    if (collections == NULL) {
+      return false;
+    }
+    ScopedPyObjectPtr mutable_sequence(PyObject_GetAttrString(
+        collections, "MutableSequence"));
+    if (mutable_sequence == NULL) {
+      return false;
+    }
+    if (ScopedPyObjectPtr(PyObject_CallMethod(mutable_sequence, "register", "O",
+                                              &RepeatedScalarContainer_Type))
+        == NULL) {
+      return false;
+    }
+    if (ScopedPyObjectPtr(PyObject_CallMethod(mutable_sequence, "register", "O",
+                                              &RepeatedCompositeContainer_Type))
+        == NULL) {
+      return false;
+    }
   }
 
-  PyObject* mutable_mapping =
-      PyObject_GetAttrString(containers, "MutableMapping");
-  Py_DECREF(containers);
+  // Initialize Map container types.
+  {
+    // ScalarMapContainer_Type derives from our MutableMapping type.
+    ScopedPyObjectPtr containers(PyImport_ImportModule(
+        "google.protobuf.internal.containers"));
+    if (containers == NULL) {
+      return false;
+    }
 
-  if (mutable_mapping == NULL) {
-    return false;
-  }
+    ScopedPyObjectPtr mutable_mapping(
+        PyObject_GetAttrString(containers, "MutableMapping"));
+    if (mutable_mapping == NULL) {
+      return false;
+    }
 
-  if (!PyObject_TypeCheck(mutable_mapping, &PyType_Type)) {
-    Py_DECREF(mutable_mapping);
-    return false;
-  }
+    if (!PyObject_TypeCheck(mutable_mapping, &PyType_Type)) {
+      return false;
+    }
 
-  ScalarMapContainer_Type.tp_base =
-      reinterpret_cast<PyTypeObject*>(mutable_mapping);
+    Py_INCREF(mutable_mapping);
+    ScalarMapContainer_Type.tp_base =
+        reinterpret_cast<PyTypeObject*>(mutable_mapping.get());
 
-  if (PyType_Ready(&ScalarMapContainer_Type) < 0) {
-    return false;
-  }
+    if (PyType_Ready(&ScalarMapContainer_Type) < 0) {
+      return false;
+    }
 
-  PyModule_AddObject(m, "ScalarMapContainer",
-                     reinterpret_cast<PyObject*>(&ScalarMapContainer_Type));
+    PyModule_AddObject(m, "ScalarMapContainer",
+                       reinterpret_cast<PyObject*>(&ScalarMapContainer_Type));
 
-  if (PyType_Ready(&ScalarMapIterator_Type) < 0) {
-    return false;
-  }
+    if (PyType_Ready(&ScalarMapIterator_Type) < 0) {
+      return false;
+    }
 
-  PyModule_AddObject(m, "ScalarMapIterator",
-                     reinterpret_cast<PyObject*>(&ScalarMapIterator_Type));
+    PyModule_AddObject(m, "ScalarMapIterator",
+                       reinterpret_cast<PyObject*>(&ScalarMapIterator_Type));
 
-  Py_INCREF(mutable_mapping);
-  MessageMapContainer_Type.tp_base =
-      reinterpret_cast<PyTypeObject*>(mutable_mapping);
+    Py_INCREF(mutable_mapping);
+    MessageMapContainer_Type.tp_base =
+        reinterpret_cast<PyTypeObject*>(mutable_mapping.get());
 
-  if (PyType_Ready(&MessageMapContainer_Type) < 0) {
-    return false;
-  }
+    if (PyType_Ready(&MessageMapContainer_Type) < 0) {
+      return false;
+    }
 
-  PyModule_AddObject(m, "MessageMapContainer",
-                     reinterpret_cast<PyObject*>(&MessageMapContainer_Type));
+    PyModule_AddObject(m, "MessageMapContainer",
+                       reinterpret_cast<PyObject*>(&MessageMapContainer_Type));
 
-  if (PyType_Ready(&MessageMapIterator_Type) < 0) {
-    return false;
-  }
+    if (PyType_Ready(&MessageMapIterator_Type) < 0) {
+      return false;
+    }
 
-  PyModule_AddObject(m, "MessageMapIterator",
-                     reinterpret_cast<PyObject*>(&MessageMapIterator_Type));
+    PyModule_AddObject(m, "MessageMapIterator",
+                       reinterpret_cast<PyObject*>(&MessageMapIterator_Type));
+  }
 
-  ExtensionDict_Type.tp_hash = PyObject_HashNotImplemented;
   if (PyType_Ready(&ExtensionDict_Type) < 0) {
     return false;
   }
-
   PyModule_AddObject(
       m, "ExtensionDict",
       reinterpret_cast<PyObject*>(&ExtensionDict_Type));
@@ -2751,6 +2942,7 @@ bool InitProto2MessageModule(PyObject *m) {
   }
   EncodeError_class = PyObject_GetAttrString(message_module, "EncodeError");
   DecodeError_class = PyObject_GetAttrString(message_module, "DecodeError");
+  PythonMessage_class = PyObject_GetAttrString(message_module, "Message");
   Py_DECREF(message_module);
 
   PyObject* pickle_module = PyImport_ImportModule("pickle");
diff --git a/python/google/protobuf/pyext/message.h b/python/google/protobuf/pyext/message.h
index 7360b207..f147d433 100644
--- a/python/google/protobuf/pyext/message.h
+++ b/python/google/protobuf/pyext/message.h
@@ -49,7 +49,6 @@ class Message;
 class Reflection;
 class FieldDescriptor;
 class Descriptor;
-class DynamicMessageFactory;
 
 using internal::shared_ptr;
 
@@ -221,9 +220,6 @@ PyObject* FindInitializationErrors(CMessage* self);
 int SetOwner(CMessage* self, const shared_ptr<Message>& new_owner);
 
 int AssureWritable(CMessage* self);
-
-DynamicMessageFactory* GetMessageFactory();
-
 }  // namespace cmessage
 
 
diff --git a/python/google/protobuf/pyext/message_map_container.cc b/python/google/protobuf/pyext/message_map_container.cc
index ab8d8fb9..a4a7fbfe 100644
--- a/python/google/protobuf/pyext/message_map_container.cc
+++ b/python/google/protobuf/pyext/message_map_container.cc
@@ -32,6 +32,7 @@
 
 #include <google/protobuf/pyext/message_map_container.h>
 
+#include <google/protobuf/stubs/logging.h>
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/message.h>
 #include <google/protobuf/pyext/message.h>
diff --git a/python/google/protobuf/pyext/repeated_composite_container.cc b/python/google/protobuf/pyext/repeated_composite_container.cc
index 86b75d0f..fe2e600b 100644
--- a/python/google/protobuf/pyext/repeated_composite_container.cc
+++ b/python/google/protobuf/pyext/repeated_composite_container.cc
@@ -38,11 +38,13 @@
 #include <google/protobuf/stubs/shared_ptr.h>
 #endif
 
+#include <google/protobuf/stubs/logging.h>
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/dynamic_message.h>
 #include <google/protobuf/message.h>
 #include <google/protobuf/pyext/descriptor.h>
+#include <google/protobuf/pyext/descriptor_pool.h>
 #include <google/protobuf/pyext/message.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
 
@@ -74,125 +76,6 @@ namespace repeated_composite_container {
     GOOGLE_CHECK((self)->parent == NULL);       \
   } while (0);
 
-// Returns a new reference.
-static PyObject* GetKey(PyObject* x) {
-  // Just the identity function.
-  Py_INCREF(x);
-  return x;
-}
-
-#define GET_KEY(keyfunc, value)                                         \
-  ((keyfunc) == NULL ?                                                  \
-  GetKey((value)) :                                                     \
-  PyObject_CallFunctionObjArgs((keyfunc), (value), NULL))
-
-// Converts a comparison function that returns -1, 0, or 1 into a
-// less-than predicate.
-//
-// Returns -1 on error, 1 if x < y, 0 if x >= y.
-static int islt(PyObject *x, PyObject *y, PyObject *compare) {
-  if (compare == NULL)
-    return PyObject_RichCompareBool(x, y, Py_LT);
-
-  ScopedPyObjectPtr res(PyObject_CallFunctionObjArgs(compare, x, y, NULL));
-  if (res == NULL)
-    return -1;
-  if (!PyInt_Check(res)) {
-    PyErr_Format(PyExc_TypeError,
-                 "comparison function must return int, not %.200s",
-                 Py_TYPE(res)->tp_name);
-    return -1;
-  }
-  return PyInt_AsLong(res) < 0;
-}
-
-// Copied from uarrsort.c but swaps memcpy swaps with protobuf/python swaps
-// TODO(anuraag): Is there a better way to do this then reinventing the wheel?
-static int InternalQuickSort(RepeatedCompositeContainer* self,
-                             Py_ssize_t start,
-                             Py_ssize_t limit,
-                             PyObject* cmp,
-                             PyObject* keyfunc) {
-  if (limit - start <= 1)
-    return 0;  // Nothing to sort.
-
-  GOOGLE_CHECK_ATTACHED(self);
-
-  Message* message = self->message;
-  const Reflection* reflection = message->GetReflection();
-  const FieldDescriptor* descriptor = self->parent_field_descriptor;
-  Py_ssize_t left;
-  Py_ssize_t right;
-
-  PyObject* children = self->child_messages;
-
-  do {
-    left = start;
-    right = limit;
-    ScopedPyObjectPtr mid(
-        GET_KEY(keyfunc, PyList_GET_ITEM(children, (start + limit) / 2)));
-    do {
-      ScopedPyObjectPtr key(GET_KEY(keyfunc, PyList_GET_ITEM(children, left)));
-      int is_lt = islt(key, mid, cmp);
-      if (is_lt == -1)
-        return -1;
-      /* array[left]<x */
-      while (is_lt) {
-        ++left;
-        ScopedPyObjectPtr key(GET_KEY(keyfunc,
-                                      PyList_GET_ITEM(children, left)));
-        is_lt = islt(key, mid, cmp);
-        if (is_lt == -1)
-          return -1;
-      }
-      key.reset(GET_KEY(keyfunc, PyList_GET_ITEM(children, right - 1)));
-      is_lt = islt(mid, key, cmp);
-      if (is_lt == -1)
-        return -1;
-      while (is_lt) {
-        --right;
-        ScopedPyObjectPtr key(GET_KEY(keyfunc,
-                                      PyList_GET_ITEM(children, right - 1)));
-        is_lt = islt(mid, key, cmp);
-        if (is_lt == -1)
-          return -1;
-      }
-      if (left < right) {
-        --right;
-        if (left < right) {
-          reflection->SwapElements(message, descriptor, left, right);
-          PyObject* tmp = PyList_GET_ITEM(children, left);
-          PyList_SET_ITEM(children, left, PyList_GET_ITEM(children, right));
-          PyList_SET_ITEM(children, right, tmp);
-        }
-        ++left;
-      }
-    } while (left < right);
-
-    if ((right - start) < (limit - left)) {
-      /* sort [start..right[ */
-      if (start < (right - 1)) {
-        InternalQuickSort(self, start, right, cmp, keyfunc);
-      }
-
-      /* sort [left..limit[ */
-      start = left;
-    } else {
-      /* sort [left..limit[ */
-      if (left < (limit - 1)) {
-        InternalQuickSort(self, left, limit, cmp, keyfunc);
-      }
-
-      /* sort [start..right[ */
-      limit = right;
-    }
-  } while (start < (limit - 1));
-
-  return 0;
-}
-
-#undef GET_KEY
-
 // ---------------------------------------------------------------------
 // len()
 
@@ -329,7 +212,7 @@ PyObject* Extend(RepeatedCompositeContainer* self, PyObject* value) {
       return NULL;
     }
     CMessage* new_cmessage = reinterpret_cast<CMessage*>(new_message.get());
-    if (cmessage::MergeFrom(new_cmessage, next) == NULL) {
+    if (ScopedPyObjectPtr(cmessage::MergeFrom(new_cmessage, next)) == NULL) {
       return NULL;
     }
   }
@@ -455,58 +338,39 @@ static PyObject* RichCompare(RepeatedCompositeContainer* self,
 // ---------------------------------------------------------------------
 // sort()
 
-static PyObject* SortAttached(RepeatedCompositeContainer* self,
-                              PyObject* args,
-                              PyObject* kwds) {
-  // Sort the underlying Message array.
-  PyObject *compare = NULL;
-  int reverse = 0;
-  PyObject *keyfunc = NULL;
-  static char *kwlist[] = {"cmp", "key", "reverse", 0};
-
-  if (args != NULL) {
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OOi:sort",
-                                     kwlist, &compare, &keyfunc, &reverse))
-      return NULL;
-  }
-  if (compare == Py_None)
-    compare = NULL;
-  if (keyfunc == Py_None)
-    keyfunc = NULL;
-
+static void ReorderAttached(RepeatedCompositeContainer* self) {
+  Message* message = self->message;
+  const Reflection* reflection = message->GetReflection();
+  const FieldDescriptor* descriptor = self->parent_field_descriptor;
   const Py_ssize_t length = Length(self);
-  if (InternalQuickSort(self, 0, length, compare, keyfunc) < 0)
-    return NULL;
-
-  // Finally reverse the result if requested.
-  if (reverse) {
-    Message* message = self->message;
-    const Reflection* reflection = message->GetReflection();
-    const FieldDescriptor* descriptor = self->parent_field_descriptor;
 
-    // Reverse the Message array.
-    for (int i = 0; i < length / 2; ++i)
-      reflection->SwapElements(message, descriptor, i, length - i - 1);
+  // Since Python protobuf objects are never arena-allocated, adding and
+  // removing message pointers to the underlying array is just updating
+  // pointers.
+  for (Py_ssize_t i = 0; i < length; ++i)
+    reflection->ReleaseLast(message, descriptor);
 
-    // Reverse the Python list.
-    ScopedPyObjectPtr res(PyObject_CallMethod(self->child_messages,
-                                              "reverse", NULL));
-    if (res == NULL)
-      return NULL;
+  for (Py_ssize_t i = 0; i < length; ++i) {
+    CMessage* py_cmsg = reinterpret_cast<CMessage*>(
+        PyList_GET_ITEM(self->child_messages, i));
+    reflection->AddAllocatedMessage(message, descriptor, py_cmsg->message);
   }
-
-  Py_RETURN_NONE;
 }
 
-static PyObject* SortReleased(RepeatedCompositeContainer* self,
-                              PyObject* args,
-                              PyObject* kwds) {
+// Returns 0 if successful; returns -1 and sets an exception if
+// unsuccessful.
+static int SortPythonMessages(RepeatedCompositeContainer* self,
+                               PyObject* args,
+                               PyObject* kwds) {
   ScopedPyObjectPtr m(PyObject_GetAttrString(self->child_messages, "sort"));
   if (m == NULL)
-    return NULL;
+    return -1;
   if (PyObject_Call(m, args, kwds) == NULL)
-    return NULL;
-  Py_RETURN_NONE;
+    return -1;
+  if (self->message != NULL) {
+    ReorderAttached(self);
+  }
+  return 0;
 }
 
 static PyObject* Sort(RepeatedCompositeContainer* self,
@@ -527,11 +391,10 @@ static PyObject* Sort(RepeatedCompositeContainer* self,
   if (UpdateChildMessages(self) < 0) {
     return NULL;
   }
-  if (self->message == NULL) {
-    return SortReleased(self, args, kwds);
-  } else {
-    return SortAttached(self, args, kwds);
+  if (SortPythonMessages(self, args, kwds) < 0) {
+    return NULL;
   }
+  Py_RETURN_NONE;
 }
 
 // ---------------------------------------------------------------------
@@ -584,18 +447,6 @@ void ReleaseLastTo(CMessage* parent,
       parent->message->GetReflection()->ReleaseLast(parent->message, field));
   // TODO(tibell): Deal with proto1.
 
-  // ReleaseMessage will return NULL which differs from
-  // child_cmessage->message, if the field does not exist.  In this case,
-  // the latter points to the default instance via a const_cast<>, so we
-  // have to reset it to a new mutable object since we are taking ownership.
-  if (released_message.get() == NULL) {
-    const Message* prototype =
-        cmessage::GetMessageFactory()->GetPrototype(
-            target->message->GetDescriptor());
-    GOOGLE_CHECK_NOTNULL(prototype);
-    released_message.reset(prototype->New());
-  }
-
   target->parent = NULL;
   target->parent_field_descriptor = NULL;
   target->message = released_message.get();
@@ -732,7 +583,7 @@ PyTypeObject RepeatedCompositeContainer_Type = {
   0,                                   //  tp_as_number
   &repeated_composite_container::SqMethods,   //  tp_as_sequence
   &repeated_composite_container::MpMethods,   //  tp_as_mapping
-  0,                                   //  tp_hash
+  PyObject_HashNotImplemented,         //  tp_hash
   0,                                   //  tp_call
   0,                                   //  tp_str
   0,                                   //  tp_getattro
diff --git a/python/google/protobuf/pyext/repeated_scalar_container.cc b/python/google/protobuf/pyext/repeated_scalar_container.cc
index fd196836..7565c6fd 100644
--- a/python/google/protobuf/pyext/repeated_scalar_container.cc
+++ b/python/google/protobuf/pyext/repeated_scalar_container.cc
@@ -39,10 +39,12 @@
 #endif
 
 #include <google/protobuf/stubs/common.h>
+#include <google/protobuf/stubs/logging.h>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/dynamic_message.h>
 #include <google/protobuf/message.h>
 #include <google/protobuf/pyext/descriptor.h>
+#include <google/protobuf/pyext/descriptor_pool.h>
 #include <google/protobuf/pyext/message.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
 
@@ -68,7 +70,7 @@ static int InternalAssignRepeatedField(
                                              self->parent_field_descriptor);
   for (Py_ssize_t i = 0; i < PyList_GET_SIZE(list); ++i) {
     PyObject* value = PyList_GET_ITEM(list, i);
-    if (Append(self, value) == NULL) {
+    if (ScopedPyObjectPtr(Append(self, value)) == NULL) {
       return -1;
     }
   }
@@ -510,7 +512,7 @@ PyObject* Extend(RepeatedScalarContainer* self, PyObject* value) {
   }
   ScopedPyObjectPtr next;
   while ((next.reset(PyIter_Next(iter))) != NULL) {
-    if (Append(self, next) == NULL) {
+    if (ScopedPyObjectPtr(Append(self, next)) == NULL) {
       return NULL;
     }
   }
@@ -690,8 +692,7 @@ static int InitializeAndCopyToParentContainer(
   if (values == NULL) {
     return -1;
   }
-  Message* new_message = cmessage::GetMessageFactory()->GetPrototype(
-      from->message->GetDescriptor())->New();
+  Message* new_message = from->message->New();
   to->parent = NULL;
   to->parent_field_descriptor = from->parent_field_descriptor;
   to->message = new_message;
@@ -781,7 +782,7 @@ PyTypeObject RepeatedScalarContainer_Type = {
   0,                                   //  tp_as_number
   &repeated_scalar_container::SqMethods,   //  tp_as_sequence
   &repeated_scalar_container::MpMethods,   //  tp_as_mapping
-  0,                                   //  tp_hash
+  PyObject_HashNotImplemented,         //  tp_hash
   0,                                   //  tp_call
   0,                                   //  tp_str
   0,                                   //  tp_getattro
diff --git a/python/google/protobuf/pyext/scalar_map_container.cc b/python/google/protobuf/pyext/scalar_map_container.cc
index 6f731d27..80d29425 100644
--- a/python/google/protobuf/pyext/scalar_map_container.cc
+++ b/python/google/protobuf/pyext/scalar_map_container.cc
@@ -32,6 +32,7 @@
 
 #include <google/protobuf/pyext/scalar_map_container.h>
 
+#include <google/protobuf/stubs/logging.h>
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/message.h>
 #include <google/protobuf/pyext/message.h>
diff --git a/python/google/protobuf/pyext/scoped_pyobject_ptr.h b/python/google/protobuf/pyext/scoped_pyobject_ptr.h
index 18ddd5cd..9979b83b 100644
--- a/python/google/protobuf/pyext/scoped_pyobject_ptr.h
+++ b/python/google/protobuf/pyext/scoped_pyobject_ptr.h
@@ -51,16 +51,22 @@ class ScopedPyObjectPtr {
 
   // Reset.  Deletes the current owned object, if any.
   // Then takes ownership of a new object, if given.
-  // this->reset(this->get()) works.
+  // This function must be called with a reference that you own.
+  //   this->reset(this->get()) is wrong!
+  //   this->reset(this->release()) is OK.
   PyObject* reset(PyObject* p = NULL) {
-    if (p != ptr_) {
-      Py_XDECREF(ptr_);
-      ptr_ = p;
-    }
+    Py_XDECREF(ptr_);
+    ptr_ = p;
     return ptr_;
   }
 
+  // ScopedPyObjectPtr should not be copied.
+  // We explicitly list and delete this overload to avoid automatic conversion
+  // to PyObject*, which is wrong in this case.
+  PyObject* reset(const ScopedPyObjectPtr& other) = delete;
+
   // Releases ownership of the object.
+  // The caller now owns the returned reference.
   PyObject* release() {
     PyObject* p = ptr_;
     ptr_ = NULL;
diff --git a/python/google/protobuf/reflection.py b/python/google/protobuf/reflection.py
index 82fca661..0c757264 100755
--- a/python/google/protobuf/reflection.py
+++ b/python/google/protobuf/reflection.py
@@ -49,101 +49,23 @@ __author__ = 'robinson@google.com (Will Robinson)'
 
 
 from google.protobuf.internal import api_implementation
-from google.protobuf import descriptor as descriptor_mod
 from google.protobuf import message
 
-_FieldDescriptor = descriptor_mod.FieldDescriptor
-
 
 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
 
-_NewMessage = message_impl.NewMessage
-_InitMessage = message_impl.InitMessage
-
-
-class GeneratedProtocolMessageType(type):
-
-  """Metaclass for protocol message classes created at runtime from Descriptors.
-
-  We add implementations for all methods described in the Message class.  We
-  also create properties to allow getting/setting all fields in the protocol
-  message.  Finally, we create slots to prevent users from accidentally
-  "setting" nonexistent fields in the protocol message, which then wouldn't get
-  serialized / deserialized properly.
-
-  The protocol compiler currently uses this metaclass to create protocol
-  message classes at runtime.  Clients can also manually create their own
-  classes at runtime, as in this example:
-
-  mydescriptor = Descriptor(.....)
-  class MyProtoClass(Message):
-    __metaclass__ = GeneratedProtocolMessageType
-    DESCRIPTOR = mydescriptor
-  myproto_instance = MyProtoClass()
-  myproto.foo_field = 23
-  ...
-
-  The above example will not work for nested types. If you wish to include them,
-  use reflection.MakeClass() instead of manually instantiating the class in
-  order to create the appropriate class structure.
-  """
-
-  # Must be consistent with the protocol-compiler code in
-  # proto2/compiler/internal/generator.*.
-  _DESCRIPTOR_KEY = 'DESCRIPTOR'
-
-  def __new__(cls, name, bases, dictionary):
-    """Custom allocation for runtime-generated class types.
-
-    We override __new__ because this is apparently the only place
-    where we can meaningfully set __slots__ on the class we're creating(?).
-    (The interplay between metaclasses and slots is not very well-documented).
-
-    Args:
-      name: Name of the class (ignored, but required by the
-        metaclass protocol).
-      bases: Base classes of the class we're constructing.
-        (Should be message.Message).  We ignore this field, but
-        it's required by the metaclass protocol
-      dictionary: The class dictionary of the class we're
-        constructing.  dictionary[_DESCRIPTOR_KEY] must contain
-        a Descriptor object describing this protocol message
-        type.
-
-    Returns:
-      Newly-allocated class.
-    """
-    descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
-    bases = _NewMessage(bases, descriptor, dictionary)
-    superclass = super(GeneratedProtocolMessageType, cls)
-
-    new_class = superclass.__new__(cls, name, bases, dictionary)
-    return new_class
-
-  def __init__(cls, name, bases, dictionary):
-    """Here we perform the majority of our work on the class.
-    We add enum getters, an __init__ method, implementations
-    of all Message methods, and properties for all fields
-    in the protocol type.
-
-    Args:
-      name: Name of the class (ignored, but required by the
-        metaclass protocol).
-      bases: Base classes of the class we're constructing.
-        (Should be message.Message).  We ignore this field, but
-        it's required by the metaclass protocol
-      dictionary: The class dictionary of the class we're
-        constructing.  dictionary[_DESCRIPTOR_KEY] must contain
-        a Descriptor object describing this protocol message
-        type.
-    """
-    descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
-    _InitMessage(descriptor, cls)
-    superclass = super(GeneratedProtocolMessageType, cls)
-    superclass.__init__(name, bases, dictionary)
+# The type of all Message classes.
+# Part of the public interface.
+#
+# Used by generated files, but clients can also use it at runtime:
+#   mydescriptor = pool.FindDescriptor(.....)
+#   class MyProtoClass(Message):
+#     __metaclass__ = GeneratedProtocolMessageType
+#     DESCRIPTOR = mydescriptor
+GeneratedProtocolMessageType = message_impl.GeneratedProtocolMessageType
 
 
 def ParseMessage(descriptor, byte_str):
diff --git a/python/google/protobuf/text_format.py b/python/google/protobuf/text_format.py
index 8cbd6822..82133765 100755
--- a/python/google/protobuf/text_format.py
+++ b/python/google/protobuf/text_format.py
@@ -113,7 +113,7 @@ def PrintMessage(message, out, indent=0, as_utf8=False, as_one_line=False,
     fields.sort(key=lambda x: x[0].index)
   for field, value in fields:
     if _IsMapEntry(field):
-      for key in value:
+      for key in sorted(value):
         # This is slow for maps with submessage entires because it copies the
         # entire tree.  Unfortunately this would take significant refactoring
         # of this file to work around.