Integrate internal changes

33 files changed, 1303 insertions, 619 deletions

diff --git a/python/google/protobuf/descriptor.py b/python/google/protobuf/descriptor.py
index 873af306..e1f2e3b7 100755
--- a/python/google/protobuf/descriptor.py
+++ b/python/google/protobuf/descriptor.py
@@ -171,13 +171,6 @@ class _NestedDescriptorBase(DescriptorBase):
     self._serialized_start = serialized_start
     self._serialized_end = serialized_end
 
-  def GetTopLevelContainingType(self):
-    """Returns the root if this is a nested type, or itself if its the root."""
-    desc = self
-    while desc.containing_type is not None:
-      desc = desc.containing_type
-    return desc
-
   def CopyToProto(self, proto):
     """Copies this to the matching proto in descriptor_pb2.
 
@@ -497,7 +490,7 @@ class FieldDescriptor(DescriptorBase):
     def __new__(cls, name, full_name, index, number, type, cpp_type, label,
                 default_value, message_type, enum_type, containing_type,
                 is_extension, extension_scope, options=None,
-                has_default_value=True, containing_oneof=None):
+                has_default_value=True, containing_oneof=None, json_name=None):
       _message.Message._CheckCalledFromGeneratedFile()
       if is_extension:
         return _message.default_pool.FindExtensionByName(full_name)
@@ -507,7 +500,7 @@ class FieldDescriptor(DescriptorBase):
   def __init__(self, name, full_name, index, number, type, cpp_type, label,
                default_value, message_type, enum_type, containing_type,
                is_extension, extension_scope, options=None,
-               has_default_value=True, containing_oneof=None):
+               has_default_value=True, containing_oneof=None, json_name=None):
     """The arguments are as described in the description of FieldDescriptor
     attributes above.
 
@@ -519,6 +512,10 @@ class FieldDescriptor(DescriptorBase):
     self.name = name
     self.full_name = full_name
     self._camelcase_name = None
+    if json_name is None:
+      self.json_name = _ToJsonName(name)
+    else:
+      self.json_name = json_name
     self.index = index
     self.number = number
     self.type = type
@@ -894,6 +891,31 @@ def _ToCamelCase(name):
   return ''.join(result)
 
 
+def _OptionsOrNone(descriptor_proto):
+  """Returns the value of the field `options`, or None if it is not set."""
+  if descriptor_proto.HasField('options'):
+    return descriptor_proto.options
+  else:
+    return None
+
+
+def _ToJsonName(name):
+  """Converts name to Json name and returns it."""
+  capitalize_next = False
+  result = []
+
+  for c in name:
+    if c == '_':
+      capitalize_next = True
+    elif capitalize_next:
+      result.append(c.upper())
+      capitalize_next = False
+    else:
+      result += c
+
+  return ''.join(result)
+
+
 def MakeDescriptor(desc_proto, package='', build_file_if_cpp=True,
                    syntax=None):
   """Make a protobuf Descriptor given a DescriptorProto protobuf.
@@ -970,6 +992,10 @@ def MakeDescriptor(desc_proto, package='', build_file_if_cpp=True,
     full_name = '.'.join(full_message_name + [field_proto.name])
     enum_desc = None
     nested_desc = None
+    if field_proto.json_name:
+      json_name = field_proto.json_name
+    else:
+      json_name = None
     if field_proto.HasField('type_name'):
       type_name = field_proto.type_name
       full_type_name = '.'.join(full_message_name +
@@ -984,10 +1010,11 @@ def MakeDescriptor(desc_proto, package='', build_file_if_cpp=True,
         field_proto.number, field_proto.type,
         FieldDescriptor.ProtoTypeToCppProtoType(field_proto.type),
         field_proto.label, None, nested_desc, enum_desc, None, False, None,
-        options=field_proto.options, has_default_value=False)
+        options=_OptionsOrNone(field_proto), has_default_value=False,
+        json_name=json_name)
     fields.append(field)
 
   desc_name = '.'.join(full_message_name)
   return Descriptor(desc_proto.name, desc_name, None, None, fields,
                     list(nested_types.values()), list(enum_types.values()), [],
-                    options=desc_proto.options)
+                    options=_OptionsOrNone(desc_proto))
diff --git a/python/google/protobuf/descriptor_pool.py b/python/google/protobuf/descriptor_pool.py
index 5c055ab9..5f43ee5f 100644
--- a/python/google/protobuf/descriptor_pool.py
+++ b/python/google/protobuf/descriptor_pool.py
@@ -62,7 +62,7 @@ from google.protobuf import descriptor_database
 from google.protobuf import text_encoding
 
 
-_USE_C_DESCRIPTORS = descriptor._USE_C_DESCRIPTORS
+_USE_C_DESCRIPTORS = descriptor._USE_C_DESCRIPTORS  # pylint: disable=protected-access
 
 
 def _NormalizeFullyQualifiedName(name):
@@ -80,6 +80,14 @@ def _NormalizeFullyQualifiedName(name):
   return name.lstrip('.')
 
 
+def _OptionsOrNone(descriptor_proto):
+  """Returns the value of the field `options`, or None if it is not set."""
+  if descriptor_proto.HasField('options'):
+    return descriptor_proto.options
+  else:
+    return None
+
+
 class DescriptorPool(object):
   """A collection of protobufs dynamically constructed by descriptor protos."""
 
@@ -326,78 +334,61 @@ class DescriptorPool(object):
           name=file_proto.name,
           package=file_proto.package,
           syntax=file_proto.syntax,
-          options=file_proto.options,
+          options=_OptionsOrNone(file_proto),
           serialized_pb=file_proto.SerializeToString(),
           dependencies=direct_deps,
           public_dependencies=public_deps)
-      if _USE_C_DESCRIPTORS:
-        # When using C++ descriptors, all objects defined in the file were added
-        # to the C++ database when the FileDescriptor was built above.
-        # Just add them to this descriptor pool.
-        def _AddMessageDescriptor(message_desc):
-          self._descriptors[message_desc.full_name] = message_desc
-          for nested in message_desc.nested_types:
-            _AddMessageDescriptor(nested)
-          for enum_type in message_desc.enum_types:
-            _AddEnumDescriptor(enum_type)
-        def _AddEnumDescriptor(enum_desc):
-          self._enum_descriptors[enum_desc.full_name] = enum_desc
-        for message_type in file_descriptor.message_types_by_name.values():
-          _AddMessageDescriptor(message_type)
-        for enum_type in file_descriptor.enum_types_by_name.values():
-          _AddEnumDescriptor(enum_type)
+      scope = {}
+
+      # This loop extracts all the message and enum types from all the
+      # dependencies of the file_proto. This is necessary to create the
+      # scope of available message types when defining the passed in
+      # file proto.
+      for dependency in built_deps:
+        scope.update(self._ExtractSymbols(
+            dependency.message_types_by_name.values()))
+        scope.update((_PrefixWithDot(enum.full_name), enum)
+                     for enum in dependency.enum_types_by_name.values())
+
+      for message_type in file_proto.message_type:
+        message_desc = self._ConvertMessageDescriptor(
+            message_type, file_proto.package, file_descriptor, scope,
+            file_proto.syntax)
+        file_descriptor.message_types_by_name[message_desc.name] = (
+            message_desc)
+
+      for enum_type in file_proto.enum_type:
+        file_descriptor.enum_types_by_name[enum_type.name] = (
+            self._ConvertEnumDescriptor(enum_type, file_proto.package,
+                                        file_descriptor, None, scope))
+
+      for index, extension_proto in enumerate(file_proto.extension):
+        extension_desc = self._MakeFieldDescriptor(
+            extension_proto, file_proto.package, index, is_extension=True)
+        extension_desc.containing_type = self._GetTypeFromScope(
+            file_descriptor.package, extension_proto.extendee, scope)
+        self._SetFieldType(extension_proto, extension_desc,
+                           file_descriptor.package, scope)
+        file_descriptor.extensions_by_name[extension_desc.name] = (
+            extension_desc)
+
+      for desc_proto in file_proto.message_type:
+        self._SetAllFieldTypes(file_proto.package, desc_proto, scope)
+
+      if file_proto.package:
+        desc_proto_prefix = _PrefixWithDot(file_proto.package)
       else:
-        scope = {}
-
-        # This loop extracts all the message and enum types from all the
-        # dependencies of the file_proto. This is necessary to create the
-        # scope of available message types when defining the passed in
-        # file proto.
-        for dependency in built_deps:
-          scope.update(self._ExtractSymbols(
-              dependency.message_types_by_name.values()))
-          scope.update((_PrefixWithDot(enum.full_name), enum)
-                       for enum in dependency.enum_types_by_name.values())
-
-        for message_type in file_proto.message_type:
-          message_desc = self._ConvertMessageDescriptor(
-              message_type, file_proto.package, file_descriptor, scope,
-              file_proto.syntax)
-          file_descriptor.message_types_by_name[message_desc.name] = (
-              message_desc)
-
-        for enum_type in file_proto.enum_type:
-          file_descriptor.enum_types_by_name[enum_type.name] = (
-              self._ConvertEnumDescriptor(enum_type, file_proto.package,
-                                          file_descriptor, None, scope))
-
-        for index, extension_proto in enumerate(file_proto.extension):
-          extension_desc = self._MakeFieldDescriptor(
-              extension_proto, file_proto.package, index, is_extension=True)
-          extension_desc.containing_type = self._GetTypeFromScope(
-              file_descriptor.package, extension_proto.extendee, scope)
-          self._SetFieldType(extension_proto, extension_desc,
-                            file_descriptor.package, scope)
-          file_descriptor.extensions_by_name[extension_desc.name] = (
-              extension_desc)
-
-        for desc_proto in file_proto.message_type:
-          self._SetAllFieldTypes(file_proto.package, desc_proto, scope)
-
-        if file_proto.package:
-          desc_proto_prefix = _PrefixWithDot(file_proto.package)
-        else:
-          desc_proto_prefix = ''
+        desc_proto_prefix = ''
 
-        for desc_proto in file_proto.message_type:
-          desc = self._GetTypeFromScope(
-              desc_proto_prefix, desc_proto.name, scope)
-          file_descriptor.message_types_by_name[desc_proto.name] = desc
+      for desc_proto in file_proto.message_type:
+        desc = self._GetTypeFromScope(
+            desc_proto_prefix, desc_proto.name, scope)
+        file_descriptor.message_types_by_name[desc_proto.name] = desc
 
-        for index, service_proto in enumerate(file_proto.service):
-          file_descriptor.services_by_name[service_proto.name] = (
-              self._MakeServiceDescriptor(service_proto, index, scope,
-                                          file_proto.package, file_descriptor))
+      for index, service_proto in enumerate(file_proto.service):
+        file_descriptor.services_by_name[service_proto.name] = (
+            self._MakeServiceDescriptor(service_proto, index, scope,
+                                        file_proto.package, file_descriptor))
 
       self.Add(file_proto)
       self._file_descriptors[file_proto.name] = file_descriptor
@@ -413,6 +404,7 @@ class DescriptorPool(object):
       package: The package the proto should be located in.
       file_desc: The file containing this message.
       scope: Dict mapping short and full symbols to message and enum types.
+      syntax: string indicating syntax of the file ("proto2" or "proto3")
 
     Returns:
       The added descriptor.
@@ -463,7 +455,7 @@ class DescriptorPool(object):
         nested_types=nested,
         enum_types=enums,
         extensions=extensions,
-        options=desc_proto.options,
+        options=_OptionsOrNone(desc_proto),
         is_extendable=is_extendable,
         extension_ranges=extension_ranges,
         file=file_desc,
@@ -517,7 +509,7 @@ class DescriptorPool(object):
                                      file=file_desc,
                                      values=values,
                                      containing_type=containing_type,
-                                     options=enum_proto.options)
+                                     options=_OptionsOrNone(enum_proto))
     scope['.%s' % enum_name] = desc
     self._enum_descriptors[enum_name] = desc
     return desc
@@ -562,7 +554,7 @@ class DescriptorPool(object):
         default_value=None,
         is_extension=is_extension,
         extension_scope=None,
-        options=field_proto.options)
+        options=_OptionsOrNone(field_proto))
 
   def _SetAllFieldTypes(self, package, desc_proto, scope):
     """Sets all the descriptor's fields's types.
@@ -681,7 +673,7 @@ class DescriptorPool(object):
         name=value_proto.name,
         index=index,
         number=value_proto.number,
-        options=value_proto.options,
+        options=_OptionsOrNone(value_proto),
         type=None)
 
   def _MakeServiceDescriptor(self, service_proto, service_index, scope,
@@ -711,7 +703,7 @@ class DescriptorPool(object):
                                         full_name=service_name,
                                         index=service_index,
                                         methods=methods,
-                                        options=service_proto.options,
+                                        options=_OptionsOrNone(service_proto),
                                         file=file_desc)
     return desc
 
@@ -740,7 +732,7 @@ class DescriptorPool(object):
                                        containing_service=None,
                                        input_type=input_type,
                                        output_type=output_type,
-                                       options=method_proto.options)
+                                       options=_OptionsOrNone(method_proto))
 
   def _ExtractSymbols(self, descriptors):
     """Pulls out all the symbols from descriptor protos.
diff --git a/python/google/protobuf/internal/any_test.proto b/python/google/protobuf/internal/any_test.proto
index cd641ca0..76a7ebd6 100644
--- a/python/google/protobuf/internal/any_test.proto
+++ b/python/google/protobuf/internal/any_test.proto
@@ -30,13 +30,21 @@
 
 // Author: jieluo@google.com (Jie Luo)
 
-syntax = "proto3";
+syntax = "proto2";
 
 package google.protobuf.internal;
 
 import "google/protobuf/any.proto";
 
 message TestAny {
-  google.protobuf.Any value = 1;
-  int32 int_value = 2;
+  optional google.protobuf.Any value = 1;
+  optional int32 int_value = 2;
+  extensions 10 to max;
+}
+
+message TestAnyExtension1 {
+  extend TestAny {
+    optional TestAnyExtension1 extension1 = 98418603;
+  }
+  optional int32 i = 15;
 }
diff --git a/python/google/protobuf/internal/containers.py b/python/google/protobuf/internal/containers.py
index ce46d08c..de13018e 100755
--- a/python/google/protobuf/internal/containers.py
+++ b/python/google/protobuf/internal/containers.py
@@ -436,9 +436,11 @@ class ScalarMap(MutableMapping):
   """Simple, type-checked, dict-like container for holding repeated scalars."""
 
   # Disallows assignment to other attributes.
-  __slots__ = ['_key_checker', '_value_checker', '_values', '_message_listener']
+  __slots__ = ['_key_checker', '_value_checker', '_values', '_message_listener',
+               '_entry_descriptor']
 
-  def __init__(self, message_listener, key_checker, value_checker):
+  def __init__(self, message_listener, key_checker, value_checker,
+               entry_descriptor):
     """
     Args:
       message_listener: A MessageListener implementation.
@@ -448,10 +450,12 @@ class ScalarMap(MutableMapping):
         inserted into this container.
       value_checker: A type_checkers.ValueChecker instance to run on values
         inserted into this container.
+      entry_descriptor: The MessageDescriptor of a map entry: key and value.
     """
     self._message_listener = message_listener
     self._key_checker = key_checker
     self._value_checker = value_checker
+    self._entry_descriptor = entry_descriptor
     self._values = {}
 
   def __getitem__(self, key):
@@ -513,6 +517,9 @@ class ScalarMap(MutableMapping):
     self._values.clear()
     self._message_listener.Modified()
 
+  def GetEntryClass(self):
+    return self._entry_descriptor._concrete_class
+
 
 class MessageMap(MutableMapping):
 
@@ -520,9 +527,10 @@ class MessageMap(MutableMapping):
 
   # Disallows assignment to other attributes.
   __slots__ = ['_key_checker', '_values', '_message_listener',
-               '_message_descriptor']
+               '_message_descriptor', '_entry_descriptor']
 
-  def __init__(self, message_listener, message_descriptor, key_checker):
+  def __init__(self, message_listener, message_descriptor, key_checker,
+               entry_descriptor):
     """
     Args:
       message_listener: A MessageListener implementation.
@@ -532,10 +540,12 @@ class MessageMap(MutableMapping):
         inserted into this container.
       value_checker: A type_checkers.ValueChecker instance to run on values
         inserted into this container.
+      entry_descriptor: The MessageDescriptor of a map entry: key and value.
     """
     self._message_listener = message_listener
     self._message_descriptor = message_descriptor
     self._key_checker = key_checker
+    self._entry_descriptor = entry_descriptor
     self._values = {}
 
   def __getitem__(self, key):
@@ -613,3 +623,6 @@ class MessageMap(MutableMapping):
   def clear(self):
     self._values.clear()
     self._message_listener.Modified()
+
+  def GetEntryClass(self):
+    return self._entry_descriptor._concrete_class
diff --git a/python/google/protobuf/internal/descriptor_pool_test.py b/python/google/protobuf/internal/descriptor_pool_test.py
index 3c8c7935..d4de2d81 100644
--- a/python/google/protobuf/internal/descriptor_pool_test.py
+++ b/python/google/protobuf/internal/descriptor_pool_test.py
@@ -119,6 +119,7 @@ class DescriptorPoolTest(unittest.TestCase):
     self.assertEqual('google.protobuf.python.internal.Factory1Message',
                      msg1.full_name)
     self.assertEqual(None, msg1.containing_type)
+    self.assertFalse(msg1.has_options)
 
     nested_msg1 = msg1.nested_types[0]
     self.assertEqual('NestedFactory1Message', nested_msg1.name)
@@ -202,6 +203,7 @@ class DescriptorPoolTest(unittest.TestCase):
     self.assertIsInstance(enum1, descriptor.EnumDescriptor)
     self.assertEqual(0, enum1.values_by_name['FACTORY_1_VALUE_0'].number)
     self.assertEqual(1, enum1.values_by_name['FACTORY_1_VALUE_1'].number)
+    self.assertFalse(enum1.has_options)
 
     nested_enum1 = self.pool.FindEnumTypeByName(
         'google.protobuf.python.internal.Factory1Message.NestedFactory1Enum')
@@ -234,6 +236,8 @@ class DescriptorPoolTest(unittest.TestCase):
         'google.protobuf.python.internal.Factory1Message.list_value')
     self.assertEqual(field.name, 'list_value')
     self.assertEqual(field.label, field.LABEL_REPEATED)
+    self.assertFalse(field.has_options)
+
     with self.assertRaises(KeyError):
       self.pool.FindFieldByName('Does not exist')
 
@@ -448,6 +452,7 @@ class EnumField(object):
     test.assertTrue(field_desc.has_default_value)
     test.assertEqual(enum_desc.values_by_name[self.default_value].number,
                      field_desc.default_value)
+    test.assertFalse(enum_desc.values_by_name[self.default_value].has_options)
     test.assertEqual(msg_desc, field_desc.containing_type)
     test.assertEqual(enum_desc, field_desc.enum_type)
 
diff --git a/python/google/protobuf/internal/descriptor_test.py b/python/google/protobuf/internal/descriptor_test.py
index 623198c8..1f148ab9 100755
--- a/python/google/protobuf/internal/descriptor_test.py
+++ b/python/google/protobuf/internal/descriptor_test.py
@@ -766,6 +766,8 @@ class MakeDescriptorTest(unittest.TestCase):
                      'Foo2.Sub.bar_field')
     self.assertEqual(result.nested_types[0].fields[0].enum_type,
                      result.nested_types[0].enum_types[0])
+    self.assertFalse(result.has_options)
+    self.assertFalse(result.fields[0].has_options)
 
   def testMakeDescriptorWithUnsignedIntField(self):
     file_descriptor_proto = descriptor_pb2.FileDescriptorProto()
@@ -818,6 +820,23 @@ class MakeDescriptorTest(unittest.TestCase):
       self.assertEqual(result.fields[index].camelcase_name,
                        camelcase_names[index])
 
+  def testJsonName(self):
+    descriptor_proto = descriptor_pb2.DescriptorProto()
+    descriptor_proto.name = 'TestJsonName'
+    names = ['field_name', 'fieldName', 'FieldName',
+             '_field_name', 'FIELD_NAME', 'json_name']
+    json_names = ['fieldName', 'fieldName', 'FieldName',
+                  'FieldName', 'FIELDNAME', '@type']
+    for index in range(len(names)):
+      field = descriptor_proto.field.add()
+      field.number = index + 1
+      field.name = names[index]
+    field.json_name = '@type'
+    result = descriptor.MakeDescriptor(descriptor_proto)
+    for index in range(len(json_names)):
+      self.assertEqual(result.fields[index].json_name,
+                       json_names[index])
+
 
 if __name__ == '__main__':
   unittest.main()
diff --git a/python/google/protobuf/internal/generator_test.py b/python/google/protobuf/internal/generator_test.py
index 83ea5f50..7f13f9da 100755
--- a/python/google/protobuf/internal/generator_test.py
+++ b/python/google/protobuf/internal/generator_test.py
@@ -227,7 +227,8 @@ class GeneratorTest(unittest.TestCase):
                      [unittest_import_pb2.DESCRIPTOR])
     self.assertEqual(unittest_import_pb2.DESCRIPTOR.dependencies,
                      [unittest_import_public_pb2.DESCRIPTOR])
-
+    self.assertEqual(unittest_import_pb2.DESCRIPTOR.public_dependencies,
+                     [unittest_import_public_pb2.DESCRIPTOR])
   def testNoGenericServices(self):
     self.assertTrue(hasattr(unittest_no_generic_services_pb2, "TestMessage"))
     self.assertTrue(hasattr(unittest_no_generic_services_pb2, "FOO"))
diff --git a/python/google/protobuf/internal/json_format_test.py b/python/google/protobuf/internal/json_format_test.py
index a5ee8ace..5ed65622 100644
--- a/python/google/protobuf/internal/json_format_test.py
+++ b/python/google/protobuf/internal/json_format_test.py
@@ -205,6 +205,15 @@ class JsonFormatTest(JsonFormatBase):
     parsed_message = json_format_proto3_pb2.TestMessage()
     self.CheckParseBack(message, parsed_message)
 
+  def testIntegersRepresentedAsFloat(self):
+    message = json_format_proto3_pb2.TestMessage()
+    json_format.Parse('{"int32Value": -2.147483648e9}', message)
+    self.assertEqual(message.int32_value, -2147483648)
+    json_format.Parse('{"int32Value": 1e5}', message)
+    self.assertEqual(message.int32_value, 100000)
+    json_format.Parse('{"int32Value": 1.0}', message)
+    self.assertEqual(message.int32_value, 1)
+
   def testMapFields(self):
     message = json_format_proto3_pb2.TestMap()
     message.bool_map[True] = 1
@@ -428,6 +437,9 @@ class JsonFormatTest(JsonFormatBase):
             '  "value": "hello",'
             '  "repeatedValue": [11.1, false, null, null]'
             '}'))
+    message.Clear()
+    json_format.Parse('{"value": null}', message)
+    self.assertEqual(message.value.WhichOneof('kind'), 'null_value')
 
   def testListValueMessage(self):
     message = json_format_proto3_pb2.TestListValue()
@@ -600,6 +612,11 @@ class JsonFormatTest(JsonFormatBase):
                       '}',
                       parsed_message)
     self.assertEqual(message, parsed_message)
+    # Null and {} should have different behavior for sub message.
+    self.assertFalse(parsed_message.HasField('message_value'))
+    json_format.Parse('{"messageValue": {}}', parsed_message)
+    self.assertTrue(parsed_message.HasField('message_value'))
+    # Null is not allowed to be used as an element in repeated field.
     self.assertRaisesRegexp(
         json_format.ParseError,
         'Failed to parse repeatedInt32Value field: '
@@ -621,15 +638,16 @@ class JsonFormatTest(JsonFormatBase):
     self.CheckError('',
                     r'Failed to load JSON: (Expecting value)|(No JSON).')
 
-  def testParseBadEnumValue(self):
-    self.CheckError(
-        '{"enumValue": 1}',
-        'Enum value must be a string literal with double quotes. '
-        'Type "proto3.EnumType" has no value named 1.')
+  def testParseEnumValue(self):
+    message = json_format_proto3_pb2.TestMessage()
+    text = '{"enumValue": 0}'
+    json_format.Parse(text, message)
+    text = '{"enumValue": 1}'
+    json_format.Parse(text, message)
     self.CheckError(
         '{"enumValue": "baz"}',
-        'Enum value must be a string literal with double quotes. '
-        'Type "proto3.EnumType" has no value named baz.')
+        'Failed to parse enumValue field: Invalid enum value baz '
+        'for enum type proto3.EnumType.')
 
   def testParseBadIdentifer(self):
     self.CheckError('{int32Value: 1}',
@@ -672,12 +690,12 @@ class JsonFormatTest(JsonFormatBase):
     text = '{"int32Value": 0x12345}'
     self.assertRaises(json_format.ParseError,
                       json_format.Parse, text, message)
+    self.CheckError('{"int32Value": 1.5}',
+                    'Failed to parse int32Value field: '
+                    'Couldn\'t parse integer: 1.5.')
     self.CheckError('{"int32Value": 012345}',
                     (r'Failed to load JSON: Expecting \'?,\'? delimiter: '
                      r'line 1.'))
-    self.CheckError('{"int32Value": 1.0}',
-                    'Failed to parse int32Value field: '
-                    'Couldn\'t parse integer: 1.0.')
     self.CheckError('{"int32Value": " 1 "}',
                     'Failed to parse int32Value field: '
                     'Couldn\'t parse integer: " 1 ".')
@@ -687,9 +705,6 @@ class JsonFormatTest(JsonFormatBase):
     self.CheckError('{"int32Value": 12345678901234567890}',
                     'Failed to parse int32Value field: Value out of range: '
                     '12345678901234567890.')
-    self.CheckError('{"int32Value": 1e5}',
-                    'Failed to parse int32Value field: '
-                    'Couldn\'t parse integer: 100000.0.')
     self.CheckError('{"uint32Value": -1}',
                     'Failed to parse uint32Value field: '
                     'Value out of range: -1.')
@@ -810,6 +825,43 @@ class JsonFormatTest(JsonFormatBase):
             r'"value": 1234}')
     json_format.Parse(text, message)
 
+  def testPreservingProtoFieldNames(self):
+    message = json_format_proto3_pb2.TestMessage()
+    message.int32_value = 12345
+    self.assertEqual('{\n  "int32Value": 12345\n}',
+                     json_format.MessageToJson(message))
+    self.assertEqual('{\n  "int32_value": 12345\n}',
+                     json_format.MessageToJson(message, False, True))
+
+    # Parsers accept both original proto field names and lowerCamelCase names.
+    message = json_format_proto3_pb2.TestMessage()
+    json_format.Parse('{"int32Value": 54321}', message)
+    self.assertEqual(54321, message.int32_value)
+    json_format.Parse('{"int32_value": 12345}', message)
+    self.assertEqual(12345, message.int32_value)
+
+  def testParseDict(self):
+    expected = 12345
+    js_dict = {'int32Value': expected}
+    message = json_format_proto3_pb2.TestMessage()
+    json_format.ParseDict(js_dict, message)
+    self.assertEqual(expected, message.int32_value)
+
+  def testMessageToDict(self):
+    message = json_format_proto3_pb2.TestMessage()
+    message.int32_value = 12345
+    expected = {'int32Value': 12345}
+    self.assertEqual(expected,
+                     json_format.MessageToDict(message))
+
+  def testJsonName(self):
+    message = json_format_proto3_pb2.TestCustomJsonName()
+    message.value = 12345
+    self.assertEqual('{\n  "@value": 12345\n}',
+                     json_format.MessageToJson(message))
+    parsed_message = json_format_proto3_pb2.TestCustomJsonName()
+    self.CheckParseBack(message, parsed_message)
+
 
 if __name__ == '__main__':
   unittest.main()
diff --git a/python/google/protobuf/internal/message_test.py b/python/google/protobuf/internal/message_test.py
index 1e95adf9..9986c0d9 100755
--- a/python/google/protobuf/internal/message_test.py
+++ b/python/google/protobuf/internal/message_test.py
@@ -67,6 +67,7 @@ from google.protobuf import text_format
 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.internal import testing_refleaks
 from google.protobuf import message
 from google.protobuf.internal import _parameterized
 
@@ -88,10 +89,13 @@ def IsNegInf(val):
   return isinf(val) and (val < 0)
 
 
-@_parameterized.Parameters(
-    (unittest_pb2),
-    (unittest_proto3_arena_pb2))
-class MessageTest(unittest.TestCase):
+BaseTestCase = testing_refleaks.BaseTestCase
+
+
+@_parameterized.NamedParameters(
+    ('_proto2', unittest_pb2),
+    ('_proto3', unittest_proto3_arena_pb2))
+class MessageTest(BaseTestCase):
 
   def testBadUtf8String(self, message_module):
     if api_implementation.Type() != 'python':
@@ -957,7 +961,7 @@ class MessageTest(unittest.TestCase):
 
 
 # Class to test proto2-only features (required, extensions, etc.)
-class Proto2Test(unittest.TestCase):
+class Proto2Test(BaseTestCase):
 
   def testFieldPresence(self):
     message = unittest_pb2.TestAllTypes()
@@ -1113,6 +1117,7 @@ class Proto2Test(unittest.TestCase):
         optional_bytes=b'x',
         optionalgroup={'a': 400},
         optional_nested_message={'bb': 500},
+        optional_foreign_message={},
         optional_nested_enum='BAZ',
         repeatedgroup=[{'a': 600},
                        {'a': 700}],
@@ -1125,8 +1130,12 @@ class Proto2Test(unittest.TestCase):
     self.assertEqual(300.5, message.optional_float)
     self.assertEqual(b'x', message.optional_bytes)
     self.assertEqual(400, message.optionalgroup.a)
-    self.assertIsInstance(message.optional_nested_message, unittest_pb2.TestAllTypes.NestedMessage)
+    self.assertIsInstance(message.optional_nested_message,
+                          unittest_pb2.TestAllTypes.NestedMessage)
     self.assertEqual(500, message.optional_nested_message.bb)
+    self.assertTrue(message.HasField('optional_foreign_message'))
+    self.assertEqual(message.optional_foreign_message,
+                     unittest_pb2.ForeignMessage())
     self.assertEqual(unittest_pb2.TestAllTypes.BAZ,
                      message.optional_nested_enum)
     self.assertEqual(2, len(message.repeatedgroup))
@@ -1164,7 +1173,7 @@ class Proto2Test(unittest.TestCase):
 
 
 # Class to test proto3-only features/behavior (updated field presence & enums)
-class Proto3Test(unittest.TestCase):
+class Proto3Test(BaseTestCase):
 
   # Utility method for comparing equality with a map.
   def assertMapIterEquals(self, map_iter, dict_value):
@@ -1720,7 +1729,7 @@ class Proto3Test(unittest.TestCase):
 
 
 
-class ValidTypeNamesTest(unittest.TestCase):
+class ValidTypeNamesTest(BaseTestCase):
 
   def assertImportFromName(self, msg, base_name):
     # Parse <type 'module.class_name'> to extra 'some.name' as a string.
@@ -1741,7 +1750,7 @@ class ValidTypeNamesTest(unittest.TestCase):
     self.assertImportFromName(pb.repeated_int32, 'Scalar')
     self.assertImportFromName(pb.repeated_nested_message, 'Composite')
 
-class PackedFieldTest(unittest.TestCase):
+class PackedFieldTest(BaseTestCase):
 
   def setMessage(self, message):
     message.repeated_int32.append(1)
@@ -1800,10 +1809,14 @@ class PackedFieldTest(unittest.TestCase):
 
 @unittest.skipIf(api_implementation.Type() != 'cpp',
                  'explicit tests of the C++ implementation')
-class OversizeProtosTest(unittest.TestCase):
-
-  def setUp(self):
-    self.file_desc = """
+class OversizeProtosTest(BaseTestCase):
+
+  @classmethod
+  def setUpClass(cls):
+    # At the moment, reference cycles between DescriptorPool and Message classes
+    # are not detected and these objects are never freed.
+    # To avoid errors with ReferenceLeakChecker, we create the class only once.
+    file_desc = """
       name: "f/f.msg2"
       package: "f"
       message_type {
@@ -1828,10 +1841,12 @@ class OversizeProtosTest(unittest.TestCase):
     """
     pool = descriptor_pool.DescriptorPool()
     desc = descriptor_pb2.FileDescriptorProto()
-    text_format.Parse(self.file_desc, desc)
+    text_format.Parse(file_desc, desc)
     pool.Add(desc)
-    self.proto_cls = message_factory.MessageFactory(pool).GetPrototype(
+    cls.proto_cls = message_factory.MessageFactory(pool).GetPrototype(
         pool.FindMessageTypeByName('f.msg2'))
+
+  def setUp(self):
     self.p = self.proto_cls()
     self.p.field.payload = 'c' * (1024 * 1024 * 64 + 1)
     self.p_serialized = self.p.SerializeToString()
diff --git a/python/google/protobuf/internal/python_message.py b/python/google/protobuf/internal/python_message.py
index c0d0ad45..60b4baad 100755
--- a/python/google/protobuf/internal/python_message.py
+++ b/python/google/protobuf/internal/python_message.py
@@ -380,13 +380,15 @@ def _GetInitializeDefaultForMap(field):
   if _IsMessageMapField(field):
     def MakeMessageMapDefault(message):
       return containers.MessageMap(
-          message._listener_for_children, value_field.message_type, key_checker)
+          message._listener_for_children, value_field.message_type, key_checker,
+          field.message_type)
     return MakeMessageMapDefault
   else:
     value_checker = type_checkers.GetTypeChecker(value_field)
     def MakePrimitiveMapDefault(message):
       return containers.ScalarMap(
-          message._listener_for_children, key_checker, value_checker)
+          message._listener_for_children, key_checker, value_checker,
+          field.message_type)
     return MakePrimitiveMapDefault
 
 def _DefaultValueConstructorForField(field):
diff --git a/python/google/protobuf/internal/reflection_test.py b/python/google/protobuf/internal/reflection_test.py
index 6f3b818a..dad79c37 100755
--- a/python/google/protobuf/internal/reflection_test.py
+++ b/python/google/protobuf/internal/reflection_test.py
@@ -60,9 +60,13 @@ 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 testing_refleaks
 from google.protobuf.internal import decoder
 
 
+BaseTestCase = testing_refleaks.BaseTestCase
+
+
 class _MiniDecoder(object):
   """Decodes a stream of values from a string.
 
@@ -108,7 +112,7 @@ class _MiniDecoder(object):
     return self._pos == len(self._bytes)
 
 
-class ReflectionTest(unittest.TestCase):
+class ReflectionTest(BaseTestCase):
 
   def assertListsEqual(self, values, others):
     self.assertEqual(len(values), len(others))
@@ -1552,6 +1556,20 @@ class ReflectionTest(unittest.TestCase):
     self.assertFalse(proto.HasField('optional_foreign_message'))
     self.assertEqual(0, proto.optional_foreign_message.c)
 
+  def testDisconnectingInOneof(self):
+    m = unittest_pb2.TestOneof2()  # This message has two messages in a oneof.
+    m.foo_message.qux_int = 5
+    sub_message = m.foo_message
+    # Accessing another message's field does not clear the first one
+    self.assertEqual(m.foo_lazy_message.qux_int, 0)
+    self.assertEqual(m.foo_message.qux_int, 5)
+    # But mutating another message in the oneof detaches the first one.
+    m.foo_lazy_message.qux_int = 6
+    self.assertEqual(m.foo_message.qux_int, 0)
+    # The reference we got above was detached and is still valid.
+    self.assertEqual(sub_message.qux_int, 5)
+    sub_message.qux_int = 7
+
   def testOneOf(self):
     proto = unittest_pb2.TestAllTypes()
     proto.oneof_uint32 = 10
@@ -1810,7 +1828,7 @@ class ReflectionTest(unittest.TestCase):
 #  into separate TestCase classes.
 
 
-class TestAllTypesEqualityTest(unittest.TestCase):
+class TestAllTypesEqualityTest(BaseTestCase):
 
   def setUp(self):
     self.first_proto = unittest_pb2.TestAllTypes()
@@ -1826,7 +1844,7 @@ class TestAllTypesEqualityTest(unittest.TestCase):
     self.assertEqual(self.first_proto, self.second_proto)
 
 
-class FullProtosEqualityTest(unittest.TestCase):
+class FullProtosEqualityTest(BaseTestCase):
 
   """Equality tests using completely-full protos as a starting point."""
 
@@ -1912,7 +1930,7 @@ class FullProtosEqualityTest(unittest.TestCase):
     self.assertEqual(self.first_proto, self.second_proto)
 
 
-class ExtensionEqualityTest(unittest.TestCase):
+class ExtensionEqualityTest(BaseTestCase):
 
   def testExtensionEquality(self):
     first_proto = unittest_pb2.TestAllExtensions()
@@ -1945,7 +1963,7 @@ class ExtensionEqualityTest(unittest.TestCase):
     self.assertEqual(first_proto, second_proto)
 
 
-class MutualRecursionEqualityTest(unittest.TestCase):
+class MutualRecursionEqualityTest(BaseTestCase):
 
   def testEqualityWithMutualRecursion(self):
     first_proto = unittest_pb2.TestMutualRecursionA()
@@ -1957,7 +1975,7 @@ class MutualRecursionEqualityTest(unittest.TestCase):
     self.assertEqual(first_proto, second_proto)
 
 
-class ByteSizeTest(unittest.TestCase):
+class ByteSizeTest(BaseTestCase):
 
   def setUp(self):
     self.proto = unittest_pb2.TestAllTypes()
@@ -2253,7 +2271,7 @@ class ByteSizeTest(unittest.TestCase):
 #   * Handling of empty submessages (with and without "has"
 #     bits set).
 
-class SerializationTest(unittest.TestCase):
+class SerializationTest(BaseTestCase):
 
   def testSerializeEmtpyMessage(self):
     first_proto = unittest_pb2.TestAllTypes()
@@ -2814,7 +2832,7 @@ class SerializationTest(unittest.TestCase):
     self.assertEqual(3, proto.repeated_int32[2])
 
 
-class OptionsTest(unittest.TestCase):
+class OptionsTest(BaseTestCase):
 
   def testMessageOptions(self):
     proto = message_set_extensions_pb2.TestMessageSet()
@@ -2841,7 +2859,7 @@ class OptionsTest(unittest.TestCase):
 
 
 
-class ClassAPITest(unittest.TestCase):
+class ClassAPITest(BaseTestCase):
 
   @unittest.skipIf(
       api_implementation.Type() == 'cpp' and api_implementation.Version() == 2,
@@ -2924,6 +2942,9 @@ class ClassAPITest(unittest.TestCase):
     text_format.Merge(file_descriptor_str, file_descriptor)
     return file_descriptor.SerializeToString()
 
+  @testing_refleaks.SkipReferenceLeakChecker('MakeDescriptor is not repeatable')
+  # This test can only run once; the second time, it raises errors about
+  # conflicting message descriptors.
   def testParsingFlatClassWithExplicitClassDeclaration(self):
     """Test that the generated class can parse a flat message."""
     # TODO(xiaofeng): This test fails with cpp implemetnation in the call
@@ -2948,6 +2969,7 @@ class ClassAPITest(unittest.TestCase):
     text_format.Merge(msg_str, msg)
     self.assertEqual(msg.flat, [0, 1, 2])
 
+  @testing_refleaks.SkipReferenceLeakChecker('MakeDescriptor is not repeatable')
   def testParsingFlatClass(self):
     """Test that the generated class can parse a flat message."""
     file_descriptor = descriptor_pb2.FileDescriptorProto()
@@ -2963,6 +2985,7 @@ class ClassAPITest(unittest.TestCase):
     text_format.Merge(msg_str, msg)
     self.assertEqual(msg.flat, [0, 1, 2])
 
+  @testing_refleaks.SkipReferenceLeakChecker('MakeDescriptor is not repeatable')
   def testParsingNestedClass(self):
     """Test that the generated class can parse a nested message."""
     file_descriptor = descriptor_pb2.FileDescriptorProto()
diff --git a/python/google/protobuf/internal/testing_refleaks.py b/python/google/protobuf/internal/testing_refleaks.py
new file mode 100644
index 00000000..b2787901
--- /dev/null
+++ b/python/google/protobuf/internal/testing_refleaks.py
@@ -0,0 +1,124 @@
+# 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.
+
+"""A subclass of unittest.TestCase which checks for reference leaks.
+
+To use:
+- Use testing_refleak.BaseTestCase instead of unittest.TestCase
+- Configure and compile Python with --with-pydebug
+
+If sys.gettotalrefcount() is not available (because Python was built without
+the Py_DEBUG option), then this module is a no-op and tests will run normally.
+"""
+
+import copy_reg
+import gc
+import sys
+
+try:
+  import unittest2 as unittest  #PY26
+except ImportError:
+  import unittest
+
+
+class LocalTestResult(unittest.TestResult):
+  """A TestResult which forwards events to a parent object, except for Skips."""
+
+  def __init__(self, parent_result):
+    unittest.TestResult.__init__(self)
+    self.parent_result = parent_result
+
+  def addError(self, test, error):
+    self.parent_result.addError(test, error)
+
+  def addFailure(self, test, error):
+    self.parent_result.addFailure(test, error)
+
+  def addSkip(self, test, reason):
+    pass
+
+
+class ReferenceLeakCheckerTestCase(unittest.TestCase):
+  """A TestCase which runs tests multiple times, collecting reference counts."""
+
+  NB_RUNS = 3
+
+  def run(self, result=None):
+    # python_message.py registers all Message classes to some pickle global
+    # registry, which makes the classes immortal.
+    # We save a copy of this registry, and reset it before we could references.
+    self._saved_pickle_registry = copy_reg.dispatch_table.copy()
+
+    # Run the test twice, to warm up the instance attributes.
+    super(ReferenceLeakCheckerTestCase, self).run(result=result)
+    super(ReferenceLeakCheckerTestCase, self).run(result=result)
+
+    oldrefcount = 0
+    local_result = LocalTestResult(result)
+
+    refcount_deltas = []
+    for _ in range(self.NB_RUNS):
+      oldrefcount = self._getRefcounts()
+      super(ReferenceLeakCheckerTestCase, self).run(result=local_result)
+      newrefcount = self._getRefcounts()
+      refcount_deltas.append(newrefcount - oldrefcount)
+    print refcount_deltas, self
+
+    try:
+      self.assertEqual(refcount_deltas, [0] * self.NB_RUNS)
+    except Exception:  # pylint: disable=broad-except
+      result.addError(self, sys.exc_info())
+
+  def _getRefcounts(self):
+    copy_reg.dispatch_table.clear()
+    copy_reg.dispatch_table.update(self._saved_pickle_registry)
+    # It is sometimes necessary to gc.collect() multiple times, to ensure
+    # that all objects can be collected.
+    gc.collect()
+    gc.collect()
+    gc.collect()
+    return sys.gettotalrefcount()
+
+
+if hasattr(sys, 'gettotalrefcount'):
+  BaseTestCase = ReferenceLeakCheckerTestCase
+  SkipReferenceLeakChecker = unittest.skip
+
+else:
+  # When PyDEBUG is not enabled, run the tests normally.
+  BaseTestCase = unittest.TestCase
+
+  def SkipReferenceLeakChecker(reason):
+    del reason  # Don't skip, so don't need a reason.
+    def Same(func):
+      return func
+    return Same
+
+
diff --git a/python/google/protobuf/internal/text_format_test.py b/python/google/protobuf/internal/text_format_test.py
index 0e38e0e9..ab481ab4 100755
--- a/python/google/protobuf/internal/text_format_test.py
+++ b/python/google/protobuf/internal/text_format_test.py
@@ -52,6 +52,7 @@ from google.protobuf import unittest_mset_pb2
 from google.protobuf import unittest_pb2
 from google.protobuf import unittest_proto3_arena_pb2
 from google.protobuf.internal import api_implementation
+from google.protobuf.internal import any_test_pb2 as test_extend_any
 from google.protobuf.internal import test_util
 from google.protobuf.internal import message_set_extensions_pb2
 from google.protobuf import descriptor_pool
@@ -684,6 +685,21 @@ class Proto2Tests(TextFormatBase):
     self.assertEqual(23, message.message_set.Extensions[ext1].i)
     self.assertEqual('foo', message.message_set.Extensions[ext2].str)
 
+  def testExtensionInsideAnyMessage(self):
+    message = test_extend_any.TestAny()
+    text = ('value {\n'
+            '  [type.googleapis.com/google.protobuf.internal.TestAny] {\n'
+            '    [google.protobuf.internal.TestAnyExtension1.extension1] {\n'
+            '      i: 10\n'
+            '    }\n'
+            '  }\n'
+            '}\n')
+    text_format.Merge(text, message, descriptor_pool=descriptor_pool.Default())
+    self.CompareToGoldenText(
+        text_format.MessageToString(
+            message, descriptor_pool=descriptor_pool.Default()),
+        text)
+
   def testParseMessageByFieldNumber(self):
     message = unittest_pb2.TestAllTypes()
     text = ('34: 1\n' 'repeated_uint64: 2\n')
@@ -1184,7 +1200,8 @@ class TokenizerTest(unittest.TestCase):
             'ID7 : "aa\\"bb"\n\n\n\n ID8: {A:inf B:-inf C:true D:false}\n'
             'ID9: 22 ID10: -111111111111111111 ID11: -22\n'
             'ID12: 2222222222222222222 ID13: 1.23456f ID14: 1.2e+2f '
-            'false_bool:  0 true_BOOL:t \n true_bool1:  1 false_BOOL1:f ')
+            'false_bool:  0 true_BOOL:t \n true_bool1:  1 false_BOOL1:f '
+            'False_bool: False True_bool: True')
     tokenizer = text_format.Tokenizer(text.splitlines())
     methods = [(tokenizer.ConsumeIdentifier, 'identifier1'), ':',
                (tokenizer.ConsumeString, 'string1'),
@@ -1228,7 +1245,11 @@ class TokenizerTest(unittest.TestCase):
                (tokenizer.ConsumeIdentifier, 'true_bool1'), ':',
                (tokenizer.ConsumeBool, True),
                (tokenizer.ConsumeIdentifier, 'false_BOOL1'), ':',
-               (tokenizer.ConsumeBool, False)]
+               (tokenizer.ConsumeBool, False),
+               (tokenizer.ConsumeIdentifier, 'False_bool'), ':',
+               (tokenizer.ConsumeBool, False),
+               (tokenizer.ConsumeIdentifier, 'True_bool'), ':',
+               (tokenizer.ConsumeBool, True)]
 
     i = 0
     while not tokenizer.AtEnd():
diff --git a/python/google/protobuf/internal/unknown_fields_test.py b/python/google/protobuf/internal/unknown_fields_test.py
index 84073f1c..d614eaa8 100755
--- a/python/google/protobuf/internal/unknown_fields_test.py
+++ b/python/google/protobuf/internal/unknown_fields_test.py
@@ -47,16 +47,20 @@ 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 testing_refleaks
 from google.protobuf.internal import type_checkers
 
 
+BaseTestCase = testing_refleaks.BaseTestCase
+
+
 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):
+class UnknownFieldsTest(BaseTestCase):
 
   def setUp(self):
     self.descriptor = unittest_pb2.TestAllTypes.DESCRIPTOR
@@ -140,7 +144,7 @@ class UnknownFieldsTest(unittest.TestCase):
         b'', message.repeated_nested_message[0].SerializeToString())
 
 
-class UnknownFieldsAccessorsTest(unittest.TestCase):
+class UnknownFieldsAccessorsTest(BaseTestCase):
 
   def setUp(self):
     self.descriptor = unittest_pb2.TestAllTypes.DESCRIPTOR
@@ -149,21 +153,18 @@ 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)
-    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.
+  # GetUnknownField() checks a detail of the Python implementation, which stores
+  # unknown fields as serialized strings. It cannot be used by the C++
+  # implementation: it's enough to check that the message is correctly
+  # serialized.
 
-  def GetField(self, name):
+  def GetUnknownField(self, name):
     field_descriptor = self.descriptor.fields_by_name[name]
     wire_type = type_checkers.FIELD_TYPE_TO_WIRE_TYPE[field_descriptor.type]
     field_tag = encoder.TagBytes(field_descriptor.number, wire_type)
     result_dict = {}
-    for tag_bytes, value in self.unknown_fields:
+    for tag_bytes, value in self.empty_message._unknown_fields:
       if tag_bytes == field_tag:
         decoder = unittest_pb2.TestAllTypes._decoders_by_tag[tag_bytes][0]
         decoder(value, 0, len(value), self.all_fields, result_dict)
@@ -171,37 +172,37 @@ class UnknownFieldsAccessorsTest(unittest.TestCase):
 
   @SkipIfCppImplementation
   def testEnum(self):
-    value = self.GetField('optional_nested_enum')
+    value = self.GetUnknownField('optional_nested_enum')
     self.assertEqual(self.all_fields.optional_nested_enum, value)
 
   @SkipIfCppImplementation
   def testRepeatedEnum(self):
-    value = self.GetField('repeated_nested_enum')
+    value = self.GetUnknownField('repeated_nested_enum')
     self.assertEqual(self.all_fields.repeated_nested_enum, value)
 
   @SkipIfCppImplementation
   def testVarint(self):
-    value = self.GetField('optional_int32')
+    value = self.GetUnknownField('optional_int32')
     self.assertEqual(self.all_fields.optional_int32, value)
 
   @SkipIfCppImplementation
   def testFixed32(self):
-    value = self.GetField('optional_fixed32')
+    value = self.GetUnknownField('optional_fixed32')
     self.assertEqual(self.all_fields.optional_fixed32, value)
 
   @SkipIfCppImplementation
   def testFixed64(self):
-    value = self.GetField('optional_fixed64')
+    value = self.GetUnknownField('optional_fixed64')
     self.assertEqual(self.all_fields.optional_fixed64, value)
 
   @SkipIfCppImplementation
   def testLengthDelimited(self):
-    value = self.GetField('optional_string')
+    value = self.GetUnknownField('optional_string')
     self.assertEqual(self.all_fields.optional_string, value)
 
   @SkipIfCppImplementation
   def testGroup(self):
-    value = self.GetField('optionalgroup')
+    value = self.GetUnknownField('optionalgroup')
     self.assertEqual(self.all_fields.optionalgroup, value)
 
   def testCopyFrom(self):
@@ -241,43 +242,41 @@ class UnknownFieldsAccessorsTest(unittest.TestCase):
     self.assertEqual(message.SerializeToString(), self.all_fields_data)
 
 
-class UnknownEnumValuesTest(unittest.TestCase):
+class UnknownEnumValuesTest(BaseTestCase):
 
   def setUp(self):
     self.descriptor = missing_enum_values_pb2.TestEnumValues.DESCRIPTOR
 
     self.message = missing_enum_values_pb2.TestEnumValues()
+    # TestEnumValues.ZERO = 0, but does not exist in the other NestedEnum.
     self.message.optional_nested_enum = (
-      missing_enum_values_pb2.TestEnumValues.ZERO)
+        missing_enum_values_pb2.TestEnumValues.ZERO)
     self.message.repeated_nested_enum.extend([
-      missing_enum_values_pb2.TestEnumValues.ZERO,
-      missing_enum_values_pb2.TestEnumValues.ONE,
-      ])
+        missing_enum_values_pb2.TestEnumValues.ZERO,
+        missing_enum_values_pb2.TestEnumValues.ONE,
+        ])
     self.message.packed_nested_enum.extend([
-      missing_enum_values_pb2.TestEnumValues.ZERO,
-      missing_enum_values_pb2.TestEnumValues.ONE,
-      ])
+        missing_enum_values_pb2.TestEnumValues.ZERO,
+        missing_enum_values_pb2.TestEnumValues.ONE,
+        ])
     self.message_data = self.message.SerializeToString()
     self.missing_message = missing_enum_values_pb2.TestMissingEnumValues()
     self.missing_message.ParseFromString(self.message_data)
-    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.
+  # GetUnknownField() checks a detail of the Python implementation, which stores
+  # unknown fields as serialized strings. It cannot be used by the C++
+  # implementation: it's enough to check that the message is correctly
+  # serialized.
 
-  def GetField(self, name):
+  def GetUnknownField(self, name):
     field_descriptor = self.descriptor.fields_by_name[name]
     wire_type = type_checkers.FIELD_TYPE_TO_WIRE_TYPE[field_descriptor.type]
     field_tag = encoder.TagBytes(field_descriptor.number, wire_type)
     result_dict = {}
-    for tag_bytes, value in self.unknown_fields:
+    for tag_bytes, value in self.missing_message._unknown_fields:
       if tag_bytes == field_tag:
         decoder = missing_enum_values_pb2.TestEnumValues._decoders_by_tag[
-          tag_bytes][0]
+            tag_bytes][0]
         decoder(value, 0, len(value), self.message, result_dict)
     return result_dict[field_descriptor]
 
@@ -294,21 +293,39 @@ class UnknownEnumValuesTest(unittest.TestCase):
     # default value.
     self.assertEqual(missing.optional_nested_enum, 0)
 
-  @SkipIfCppImplementation
   def testUnknownEnumValue(self):
+    if api_implementation.Type() == 'cpp':
+      # The CPP implementation of protos (wrongly) allows unknown enum values
+      # for proto2.
+      self.assertTrue(self.missing_message.HasField('optional_nested_enum'))
+      self.assertEqual(self.message.optional_nested_enum,
+                       self.missing_message.optional_nested_enum)
+    else:
+      # On the other hand, the Python implementation considers unknown values
+      # as unknown fields. This is the correct behavior.
+      self.assertFalse(self.missing_message.HasField('optional_nested_enum'))
+      value = self.GetUnknownField('optional_nested_enum')
+      self.assertEqual(self.message.optional_nested_enum, value)
+    self.missing_message.ClearField('optional_nested_enum')
     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)
+    if api_implementation.Type() == 'cpp':
+      # For repeated enums, both implementations agree.
+      self.assertEqual([], self.missing_message.repeated_nested_enum)
+    else:
+      self.assertEqual([], self.missing_message.repeated_nested_enum)
+      value = self.GetUnknownField('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)
+    if api_implementation.Type() == 'cpp':
+      # For repeated enums, both implementations agree.
+      self.assertEqual([], self.missing_message.packed_nested_enum)
+    else:
+      self.assertEqual([], self.missing_message.packed_nested_enum)
+      value = self.GetUnknownField('packed_nested_enum')
+      self.assertEqual(self.message.packed_nested_enum, value)
 
   def testRoundTrip(self):
     new_message = missing_enum_values_pb2.TestEnumValues()
diff --git a/python/google/protobuf/internal/well_known_types.py b/python/google/protobuf/internal/well_known_types.py
index 7c5dffd0..d631abee 100644
--- a/python/google/protobuf/internal/well_known_types.py
+++ b/python/google/protobuf/internal/well_known_types.py
@@ -53,6 +53,7 @@ _NANOS_PER_MICROSECOND = 1000
 _MILLIS_PER_SECOND = 1000
 _MICROS_PER_SECOND = 1000000
 _SECONDS_PER_DAY = 24 * 3600
+_DURATION_SECONDS_MAX = 315576000000
 
 
 class Error(Exception):
@@ -247,6 +248,7 @@ class Duration(object):
       represent the exact Duration value. For example: "1s", "1.010s",
       "1.000000100s", "-3.100s"
     """
+    _CheckDurationValid(self.seconds, self.nanos)
     if self.seconds < 0 or self.nanos < 0:
       result = '-'
       seconds = - self.seconds + int((0 - self.nanos) // 1e9)
@@ -286,14 +288,17 @@ class Duration(object):
     try:
       pos = value.find('.')
       if pos == -1:
-        self.seconds = int(value[:-1])
-        self.nanos = 0
+        seconds = int(value[:-1])
+        nanos = 0
       else:
-        self.seconds = int(value[:pos])
+        seconds = int(value[:pos])
         if value[0] == '-':
-          self.nanos = int(round(float('-0{0}'.format(value[pos: -1])) *1e9))
+          nanos = int(round(float('-0{0}'.format(value[pos: -1])) *1e9))
         else:
-          self.nanos = int(round(float('0{0}'.format(value[pos: -1])) *1e9))
+          nanos = int(round(float('0{0}'.format(value[pos: -1])) *1e9))
+      _CheckDurationValid(seconds, nanos)
+      self.seconds = seconds
+      self.nanos = nanos
     except ValueError:
       raise ParseError(
           'Couldn\'t parse duration: {0}.'.format(value))
@@ -359,6 +364,17 @@ class Duration(object):
     self.nanos = nanos
 
 
+def _CheckDurationValid(seconds, nanos):
+  if seconds < -_DURATION_SECONDS_MAX or seconds > _DURATION_SECONDS_MAX:
+    raise Error(
+        'Duration is not valid: Seconds {0} must be in range '
+        '[-315576000000, 315576000000].'.format(seconds))
+  if nanos <= -_NANOS_PER_SECOND or nanos >= _NANOS_PER_SECOND:
+    raise Error(
+        'Duration is not valid: Nanos {0} must be in range '
+        '[-999999999, 999999999].'.format(nanos))
+
+
 def _RoundTowardZero(value, divider):
   """Truncates the remainder part after division."""
   # For some languanges, the sign of the remainder is implementation
@@ -379,13 +395,16 @@ class FieldMask(object):
 
   def ToJsonString(self):
     """Converts FieldMask to string according to proto3 JSON spec."""
-    return ','.join(self.paths)
+    camelcase_paths = []
+    for path in self.paths:
+      camelcase_paths.append(_SnakeCaseToCamelCase(path))
+    return ','.join(camelcase_paths)
 
   def FromJsonString(self, value):
     """Converts string to FieldMask according to proto3 JSON spec."""
     self.Clear()
     for path in value.split(','):
-      self.paths.append(path)
+      self.paths.append(_CamelCaseToSnakeCase(path))
 
   def IsValidForDescriptor(self, message_descriptor):
     """Checks whether the FieldMask is valid for Message Descriptor."""
@@ -472,6 +491,48 @@ def _CheckFieldMaskMessage(message):
         message_descriptor.full_name))
 
 
+def _SnakeCaseToCamelCase(path_name):
+  """Converts a path name from snake_case to camelCase."""
+  result = []
+  after_underscore = False
+  for c in path_name:
+    if c.isupper():
+      raise Error('Fail to print FieldMask to Json string: Path name '
+                  '{0} must not contain uppercase letters.'.format(path_name))
+    if after_underscore:
+      if c.islower():
+        result.append(c.upper())
+        after_underscore = False
+      else:
+        raise Error('Fail to print FieldMask to Json string: The '
+                    'character after a "_" must be a lowercase letter '
+                    'in path name {0}.'.format(path_name))
+    elif c == '_':
+      after_underscore = True
+    else:
+      result += c
+
+  if after_underscore:
+    raise Error('Fail to print FieldMask to Json string: Trailing "_" '
+                'in path name {0}.'.format(path_name))
+  return ''.join(result)
+
+
+def _CamelCaseToSnakeCase(path_name):
+  """Converts a field name from camelCase to snake_case."""
+  result = []
+  for c in path_name:
+    if c == '_':
+      raise ParseError('Fail to parse FieldMask: Path name '
+                       '{0} must not contain "_"s.'.format(path_name))
+    if c.isupper():
+      result += '_'
+      result += c.lower()
+    else:
+      result += c
+  return ''.join(result)
+
+
 class _FieldMaskTree(object):
   """Represents a FieldMask in a tree structure.
 
diff --git a/python/google/protobuf/internal/well_known_types_test.py b/python/google/protobuf/internal/well_known_types_test.py
index 2f32ac99..077f630f 100644
--- a/python/google/protobuf/internal/well_known_types_test.py
+++ b/python/google/protobuf/internal/well_known_types_test.py
@@ -303,6 +303,25 @@ class TimeUtilTest(TimeUtilTestBase):
         well_known_types.ParseError,
         'Couldn\'t parse duration: 1...2s.',
         message.FromJsonString, '1...2s')
+    text = '-315576000001.000000000s'
+    self.assertRaisesRegexp(
+        well_known_types.Error,
+        r'Duration is not valid\: Seconds -315576000001 must be in range'
+        r' \[-315576000000\, 315576000000\].',
+        message.FromJsonString, text)
+    text = '315576000001.000000000s'
+    self.assertRaisesRegexp(
+        well_known_types.Error,
+        r'Duration is not valid\: Seconds 315576000001 must be in range'
+        r' \[-315576000000\, 315576000000\].',
+        message.FromJsonString, text)
+    message.seconds = -315576000001
+    message.nanos = 0
+    self.assertRaisesRegexp(
+        well_known_types.Error,
+        r'Duration is not valid\: Seconds -315576000001 must be in range'
+        r' \[-315576000000\, 315576000000\].',
+        message.ToJsonString)
 
 
 class FieldMaskTest(unittest.TestCase):
@@ -322,6 +341,20 @@ class FieldMaskTest(unittest.TestCase):
     mask.FromJsonString('foo,bar')
     self.assertEqual(['foo', 'bar'], mask.paths)
 
+    # Test camel case
+    mask.Clear()
+    mask.paths.append('foo_bar')
+    self.assertEqual('fooBar', mask.ToJsonString())
+    mask.paths.append('bar_quz')
+    self.assertEqual('fooBar,barQuz', mask.ToJsonString())
+
+    mask.FromJsonString('')
+    self.assertEqual('', mask.ToJsonString())
+    mask.FromJsonString('fooBar')
+    self.assertEqual(['foo_bar'], mask.paths)
+    mask.FromJsonString('fooBar,barQuz')
+    self.assertEqual(['foo_bar', 'bar_quz'], mask.paths)
+
   def testDescriptorToFieldMask(self):
     mask = field_mask_pb2.FieldMask()
     msg_descriptor = unittest_pb2.TestAllTypes.DESCRIPTOR
@@ -502,17 +535,68 @@ class FieldMaskTest(unittest.TestCase):
     nested_src.payload.repeated_int32.append(1234)
     nested_dst.payload.repeated_int32.append(5678)
     # Repeated fields will be appended by default.
-    mask.FromJsonString('payload.repeated_int32')
+    mask.FromJsonString('payload.repeatedInt32')
     mask.MergeMessage(nested_src, nested_dst)
     self.assertEqual(2, len(nested_dst.payload.repeated_int32))
     self.assertEqual(5678, nested_dst.payload.repeated_int32[0])
     self.assertEqual(1234, nested_dst.payload.repeated_int32[1])
     # Change the behavior to replace repeated fields.
-    mask.FromJsonString('payload.repeated_int32')
+    mask.FromJsonString('payload.repeatedInt32')
     mask.MergeMessage(nested_src, nested_dst, False, True)
     self.assertEqual(1, len(nested_dst.payload.repeated_int32))
     self.assertEqual(1234, nested_dst.payload.repeated_int32[0])
 
+  def testSnakeCaseToCamelCase(self):
+    self.assertEqual('fooBar',
+                     well_known_types._SnakeCaseToCamelCase('foo_bar'))
+    self.assertEqual('FooBar',
+                     well_known_types._SnakeCaseToCamelCase('_foo_bar'))
+    self.assertEqual('foo3Bar',
+                     well_known_types._SnakeCaseToCamelCase('foo3_bar'))
+
+    # No uppercase letter is allowed.
+    self.assertRaisesRegexp(
+        well_known_types.Error,
+        'Fail to print FieldMask to Json string: Path name Foo must '
+        'not contain uppercase letters.',
+        well_known_types._SnakeCaseToCamelCase,
+        'Foo')
+    # Any character after a "_" must be a lowercase letter.
+    #   1. "_" cannot be followed by another "_".
+    #   2. "_" cannot be followed by a digit.
+    #   3. "_" cannot appear as the last character.
+    self.assertRaisesRegexp(
+        well_known_types.Error,
+        'Fail to print FieldMask to Json string: The character after a '
+        '"_" must be a lowercase letter in path name foo__bar.',
+        well_known_types._SnakeCaseToCamelCase,
+        'foo__bar')
+    self.assertRaisesRegexp(
+        well_known_types.Error,
+        'Fail to print FieldMask to Json string: The character after a '
+        '"_" must be a lowercase letter in path name foo_3bar.',
+        well_known_types._SnakeCaseToCamelCase,
+        'foo_3bar')
+    self.assertRaisesRegexp(
+        well_known_types.Error,
+        'Fail to print FieldMask to Json string: Trailing "_" in path '
+        'name foo_bar_.',
+        well_known_types._SnakeCaseToCamelCase,
+        'foo_bar_')
+
+  def testCamelCaseToSnakeCase(self):
+    self.assertEqual('foo_bar',
+                     well_known_types._CamelCaseToSnakeCase('fooBar'))
+    self.assertEqual('_foo_bar',
+                     well_known_types._CamelCaseToSnakeCase('FooBar'))
+    self.assertEqual('foo3_bar',
+                     well_known_types._CamelCaseToSnakeCase('foo3Bar'))
+    self.assertRaisesRegexp(
+        well_known_types.ParseError,
+        'Fail to parse FieldMask: Path name foo_bar must not contain "_"s.',
+        well_known_types._CamelCaseToSnakeCase,
+        'foo_bar')
+
 
 class StructTest(unittest.TestCase):
 
@@ -529,52 +613,52 @@ class StructTest(unittest.TestCase):
     struct_list.add_struct()['subkey2'] = 9
 
     self.assertTrue(isinstance(struct, well_known_types.Struct))
-    self.assertEquals(5, struct['key1'])
-    self.assertEquals('abc', struct['key2'])
+    self.assertEqual(5, struct['key1'])
+    self.assertEqual('abc', struct['key2'])
     self.assertIs(True, struct['key3'])
-    self.assertEquals(11, struct['key4']['subkey'])
+    self.assertEqual(11, struct['key4']['subkey'])
     inner_struct = struct_class()
     inner_struct['subkey2'] = 9
-    self.assertEquals([6, 'seven', True, False, None, inner_struct],
-                      list(struct['key5'].items()))
+    self.assertEqual([6, 'seven', True, False, None, inner_struct],
+                     list(struct['key5'].items()))
 
     serialized = struct.SerializeToString()
 
     struct2 = struct_pb2.Struct()
     struct2.ParseFromString(serialized)
 
-    self.assertEquals(struct, struct2)
+    self.assertEqual(struct, struct2)
 
     self.assertTrue(isinstance(struct2, well_known_types.Struct))
-    self.assertEquals(5, struct2['key1'])
-    self.assertEquals('abc', struct2['key2'])
+    self.assertEqual(5, struct2['key1'])
+    self.assertEqual('abc', struct2['key2'])
     self.assertIs(True, struct2['key3'])
-    self.assertEquals(11, struct2['key4']['subkey'])
-    self.assertEquals([6, 'seven', True, False, None, inner_struct],
-                      list(struct2['key5'].items()))
+    self.assertEqual(11, struct2['key4']['subkey'])
+    self.assertEqual([6, 'seven', True, False, None, inner_struct],
+                     list(struct2['key5'].items()))
 
     struct_list = struct2['key5']
-    self.assertEquals(6, struct_list[0])
-    self.assertEquals('seven', struct_list[1])
-    self.assertEquals(True, struct_list[2])
-    self.assertEquals(False, struct_list[3])
-    self.assertEquals(None, struct_list[4])
-    self.assertEquals(inner_struct, struct_list[5])
+    self.assertEqual(6, struct_list[0])
+    self.assertEqual('seven', struct_list[1])
+    self.assertEqual(True, struct_list[2])
+    self.assertEqual(False, struct_list[3])
+    self.assertEqual(None, struct_list[4])
+    self.assertEqual(inner_struct, struct_list[5])
 
     struct_list[1] = 7
-    self.assertEquals(7, struct_list[1])
+    self.assertEqual(7, struct_list[1])
 
     struct_list.add_list().extend([1, 'two', True, False, None])
-    self.assertEquals([1, 'two', True, False, None],
-                      list(struct_list[6].items()))
+    self.assertEqual([1, 'two', True, False, None],
+                     list(struct_list[6].items()))
 
     text_serialized = str(struct)
     struct3 = struct_pb2.Struct()
     text_format.Merge(text_serialized, struct3)
-    self.assertEquals(struct, struct3)
+    self.assertEqual(struct, struct3)
 
     struct.get_or_create_struct('key3')['replace'] = 12
-    self.assertEquals(12, struct['key3']['replace'])
+    self.assertEqual(12, struct['key3']['replace'])
 
 
 class AnyTest(unittest.TestCase):
diff --git a/python/google/protobuf/json_format.py b/python/google/protobuf/json_format.py
index edc0cb50..c42371d0 100644
--- a/python/google/protobuf/json_format.py
+++ b/python/google/protobuf/json_format.py
@@ -86,7 +86,9 @@ class ParseError(Error):
   """Thrown in case of parsing error."""
 
 
-def MessageToJson(message, including_default_value_fields=False):
+def MessageToJson(message,
+                  including_default_value_fields=False,
+                  preserving_proto_field_name=False):
   """Converts protobuf message to JSON format.
 
   Args:
@@ -95,14 +97,42 @@ def MessageToJson(message, including_default_value_fields=False):
         repeated fields, and map fields will always be serialized.  If
         False, only serialize non-empty fields.  Singular message fields
         and oneof fields are not affected by this option.
+    preserving_proto_field_name: If True, use the original proto field
+        names as defined in the .proto file. If False, convert the field
+        names to lowerCamelCase.
 
   Returns:
     A string containing the JSON formatted protocol buffer message.
   """
-  printer = _Printer(including_default_value_fields)
+  printer = _Printer(including_default_value_fields,
+                     preserving_proto_field_name)
   return printer.ToJsonString(message)
 
 
+def MessageToDict(message,
+                  including_default_value_fields=False,
+                  preserving_proto_field_name=False):
+  """Converts protobuf message to a JSON dictionary.
+
+  Args:
+    message: The protocol buffers message instance to serialize.
+    including_default_value_fields: If True, singular primitive fields,
+        repeated fields, and map fields will always be serialized.  If
+        False, only serialize non-empty fields.  Singular message fields
+        and oneof fields are not affected by this option.
+    preserving_proto_field_name: If True, use the original proto field
+        names as defined in the .proto file. If False, convert the field
+        names to lowerCamelCase.
+
+  Returns:
+    A dict representation of the JSON formatted protocol buffer message.
+  """
+  printer = _Printer(including_default_value_fields,
+                     preserving_proto_field_name)
+  # pylint: disable=protected-access
+  return printer._MessageToJsonObject(message)
+
+
 def _IsMapEntry(field):
   return (field.type == descriptor.FieldDescriptor.TYPE_MESSAGE and
           field.message_type.has_options and
@@ -113,8 +143,10 @@ class _Printer(object):
   """JSON format printer for protocol message."""
 
   def __init__(self,
-               including_default_value_fields=False):
+               including_default_value_fields=False,
+               preserving_proto_field_name=False):
     self.including_default_value_fields = including_default_value_fields
+    self.preserving_proto_field_name = preserving_proto_field_name
 
   def ToJsonString(self, message):
     js = self._MessageToJsonObject(message)
@@ -137,7 +169,10 @@ class _Printer(object):
 
     try:
       for field, value in fields:
-        name = field.camelcase_name
+        if self.preserving_proto_field_name:
+          name = field.name
+        else:
+          name = field.json_name
         if _IsMapEntry(field):
           # Convert a map field.
           v_field = field.message_type.fields_by_name['value']
@@ -169,7 +204,10 @@ class _Printer(object):
                field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_MESSAGE) or
               field.containing_oneof):
             continue
-          name = field.camelcase_name
+          if self.preserving_proto_field_name:
+            name = field.name
+          else:
+            name = field.json_name
           if name in js:
             # Skip the field which has been serailized already.
             continue
@@ -328,8 +366,22 @@ def Parse(text, message, ignore_unknown_fields=False):
       js = json.loads(text, object_pairs_hook=_DuplicateChecker)
   except ValueError as e:
     raise ParseError('Failed to load JSON: {0}.'.format(str(e)))
+  return ParseDict(js, message, ignore_unknown_fields)
+
+
+def ParseDict(js_dict, message, ignore_unknown_fields=False):
+  """Parses a JSON dictionary representation into a message.
+
+  Args:
+    js_dict: Dict representation of a JSON message.
+    message: A protocol buffer message to merge into.
+    ignore_unknown_fields: If True, do not raise errors for unknown fields.
+
+  Returns:
+    The same message passed as argument.
+  """
   parser = _Parser(ignore_unknown_fields)
-  parser.ConvertMessage(js, message)
+  parser.ConvertMessage(js_dict, message)
   return message
 
 
@@ -374,9 +426,13 @@ class _Parser(object):
     """
     names = []
     message_descriptor = message.DESCRIPTOR
+    fields_by_json_name = dict((f.json_name, f)
+                               for f in message_descriptor.fields)
     for name in js:
       try:
-        field = message_descriptor.fields_by_camelcase_name.get(name, None)
+        field = fields_by_json_name.get(name, None)
+        if not field:
+          field = message_descriptor.fields_by_name.get(name, None)
         if not field:
           if self.ignore_unknown_fields:
             continue
@@ -399,7 +455,12 @@ class _Parser(object):
 
         value = js[name]
         if value is None:
-          message.ClearField(field.name)
+          if (field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_MESSAGE
+              and field.message_type.full_name == 'google.protobuf.Value'):
+            sub_message = getattr(message, field.name)
+            sub_message.null_value = 0
+          else:
+            message.ClearField(field.name)
           continue
 
         # Parse field value.
@@ -431,6 +492,7 @@ class _Parser(object):
                   _ConvertScalarFieldValue(item, field))
         elif field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_MESSAGE:
           sub_message = getattr(message, field.name)
+          sub_message.SetInParent()
           self.ConvertMessage(value, sub_message)
         else:
           setattr(message, field.name, _ConvertScalarFieldValue(value, field))
@@ -574,10 +636,15 @@ def _ConvertScalarFieldValue(value, field, require_str=False):
     # Convert an enum value.
     enum_value = field.enum_type.values_by_name.get(value, None)
     if enum_value is None:
-      raise ParseError(
-          'Enum value must be a string literal with double quotes. '
-          'Type "{0}" has no value named {1}.'.format(
-              field.enum_type.full_name, value))
+      try:
+        number = int(value)
+        enum_value = field.enum_type.values_by_number.get(number, None)
+      except ValueError:
+        raise ParseError('Invalid enum value {0} for enum type {1}.'.format(
+            value, field.enum_type.full_name))
+      if enum_value is None:
+        raise ParseError('Invalid enum value {0} for enum type {1}.'.format(
+            value, field.enum_type.full_name))
     return enum_value.number
 
 
@@ -593,7 +660,7 @@ def _ConvertInteger(value):
   Raises:
     ParseError: If an integer couldn't be consumed.
   """
-  if isinstance(value, float):
+  if isinstance(value, float) and not value.is_integer():
     raise ParseError('Couldn\'t parse integer: {0}.'.format(value))
 
   if isinstance(value, six.text_type) and value.find(' ') != -1:
diff --git a/python/google/protobuf/message.py b/python/google/protobuf/message.py
index 606f735f..aab250e4 100755
--- a/python/google/protobuf/message.py
+++ b/python/google/protobuf/message.py
@@ -225,10 +225,11 @@ class Message(object):
   # """
   def ListFields(self):
     """Returns a list of (FieldDescriptor, value) tuples for all
-    fields in the message which are not empty.  A singular field is non-empty
-    if HasField() would return true, and a repeated field is non-empty if
-    it contains at least one element.  The fields are ordered by field
-    number"""
+    fields in the message which are not empty.  A message field is
+    non-empty if HasField() would return true. A singular primitive field
+    is non-empty if HasField() would return true in proto2 or it is non zero
+    in proto3. A repeated field is non-empty if it contains at least one
+    element.  The fields are ordered by field number"""
     raise NotImplementedError
 
   def HasField(self, field_name):
diff --git a/python/google/protobuf/message_factory.py b/python/google/protobuf/message_factory.py
index 1b059d13..8ab1c513 100644
--- a/python/google/protobuf/message_factory.py
+++ b/python/google/protobuf/message_factory.py
@@ -103,13 +103,8 @@ class MessageFactory(object):
     result = {}
     for file_name in files:
       file_desc = self.pool.FindFileByName(file_name)
-      for name, msg in file_desc.message_types_by_name.items():
-        if file_desc.package:
-          full_name = '.'.join([file_desc.package, name])
-        else:
-          full_name = msg.name
-        result[full_name] = self.GetPrototype(
-            self.pool.FindMessageTypeByName(full_name))
+      for desc in file_desc.message_types_by_name.values():
+        result[desc.full_name] = self.GetPrototype(desc)
 
       # While the extension FieldDescriptors are created by the descriptor pool,
       # the python classes created in the factory need them to be registered
@@ -120,7 +115,7 @@ class MessageFactory(object):
       # ignore the registration if the original was the same, or raise
       # an error if they were different.
 
-      for name, extension in file_desc.extensions_by_name.items():
+      for extension in file_desc.extensions_by_name.values():
         if extension.containing_type.full_name not in self._classes:
           self.GetPrototype(extension.containing_type)
         extended_class = self._classes[extension.containing_type.full_name]
diff --git a/python/google/protobuf/pyext/descriptor.cc b/python/google/protobuf/pyext/descriptor.cc
index e6ef5ef5..924ae0b9 100644
--- a/python/google/protobuf/pyext/descriptor.cc
+++ b/python/google/protobuf/pyext/descriptor.cc
@@ -41,6 +41,7 @@
 #include <google/protobuf/pyext/descriptor_containers.h>
 #include <google/protobuf/pyext/descriptor_pool.h>
 #include <google/protobuf/pyext/message.h>
+#include <google/protobuf/pyext/message_factory.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
 
 #if PY_MAJOR_VERSION >= 3
@@ -204,8 +205,9 @@ static PyObject* GetOrBuildOptions(const DescriptorClass *descriptor) {
   // read-only instance.
   const Message& options(descriptor->options());
   const Descriptor *message_type = options.GetDescriptor();
-  CMessageClass* message_class(
-      cdescriptor_pool::GetMessageClass(pool, message_type));
+  PyMessageFactory* message_factory = pool->py_message_factory;
+  CMessageClass* message_class = message_factory::GetMessageClass(
+      message_factory, message_type);
   if (message_class == NULL) {
     // The Options message was not found in the current DescriptorPool.
     // This means that the pool cannot contain any extensions to the Options
@@ -213,7 +215,9 @@ static PyObject* GetOrBuildOptions(const DescriptorClass *descriptor) {
     // the chances of successfully parsing the options.
     PyErr_Clear();
     pool = GetDefaultDescriptorPool();
-    message_class = cdescriptor_pool::GetMessageClass(pool, message_type);
+    message_factory = pool->py_message_factory;
+    message_class = message_factory::GetMessageClass(
+      message_factory, message_type);
   }
   if (message_class == NULL) {
     PyErr_Format(PyExc_TypeError, "Could not retrieve class for Options: %s",
@@ -243,7 +247,7 @@ static PyObject* GetOrBuildOptions(const DescriptorClass *descriptor) {
     options.SerializeToString(&serialized);
     io::CodedInputStream input(
         reinterpret_cast<const uint8*>(serialized.c_str()), serialized.size());
-    input.SetExtensionRegistry(pool->pool, pool->message_factory);
+    input.SetExtensionRegistry(pool->pool, message_factory->message_factory);
     bool success = cmsg->message->MergePartialFromCodedStream(&input);
     if (!success) {
       PyErr_Format(PyExc_ValueError, "Error parsing Options message");
@@ -439,8 +443,9 @@ static PyObject* GetConcreteClass(PyBaseDescriptor* self, void *closure) {
   // which contains this descriptor.
   // This might not be the one you expect! For example the returned object does
   // not know about extensions defined in a custom pool.
-  CMessageClass* concrete_class(cdescriptor_pool::GetMessageClass(
-      GetDescriptorPool_FromPool(_GetDescriptor(self)->file()->pool()),
+  CMessageClass* concrete_class(message_factory::GetMessageClass(
+      GetDescriptorPool_FromPool(
+          _GetDescriptor(self)->file()->pool())->py_message_factory,
       _GetDescriptor(self)));
   Py_XINCREF(concrete_class);
   return concrete_class->AsPyObject();
@@ -699,6 +704,10 @@ static PyObject* GetCamelcaseName(PyBaseDescriptor* self, void *closure) {
   return PyString_FromCppString(_GetDescriptor(self)->camelcase_name());
 }
 
+static PyObject* GetJsonName(PyBaseDescriptor* self, void *closure) {
+  return PyString_FromCppString(_GetDescriptor(self)->json_name());
+}
+
 static PyObject* GetType(PyBaseDescriptor *self, void *closure) {
   return PyInt_FromLong(_GetDescriptor(self)->type());
 }
@@ -888,6 +897,7 @@ static PyGetSetDef Getters[] = {
   { "full_name", (getter)GetFullName, NULL, "Full name"},
   { "name", (getter)GetName, NULL, "Unqualified name"},
   { "camelcase_name", (getter)GetCamelcaseName, NULL, "Camelcase name"},
+  { "json_name", (getter)GetJsonName, NULL, "Json name"},
   { "type", (getter)GetType, NULL, "C++ Type"},
   { "cpp_type", (getter)GetCppType, NULL, "C++ Type"},
   { "label", (getter)GetLabel, NULL, "Label"},
diff --git a/python/google/protobuf/pyext/descriptor_pool.cc b/python/google/protobuf/pyext/descriptor_pool.cc
index cfd98690..a42e5431 100644
--- a/python/google/protobuf/pyext/descriptor_pool.cc
+++ b/python/google/protobuf/pyext/descriptor_pool.cc
@@ -33,11 +33,11 @@
 #include <Python.h>
 
 #include <google/protobuf/descriptor.pb.h>
-#include <google/protobuf/dynamic_message.h>
 #include <google/protobuf/pyext/descriptor.h>
 #include <google/protobuf/pyext/descriptor_database.h>
 #include <google/protobuf/pyext/descriptor_pool.h>
 #include <google/protobuf/pyext/message.h>
+#include <google/protobuf/pyext/message_factory.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
 
 #if PY_MAJOR_VERSION >= 3
@@ -73,18 +73,16 @@ static PyDescriptorPool* _CreateDescriptorPool() {
   cpool->underlay = NULL;
   cpool->database = NULL;
 
-  DynamicMessageFactory* message_factory = new DynamicMessageFactory();
-  // This option might be the default some day.
-  message_factory->SetDelegateToGeneratedFactory(true);
-  cpool->message_factory = message_factory;
-
-  // TODO(amauryfa): Rewrite the SymbolDatabase in C so that it uses the same
-  // storage.
-  cpool->classes_by_descriptor =
-      new PyDescriptorPool::ClassesByMessageMap();
   cpool->descriptor_options =
       new hash_map<const void*, PyObject *>();
 
+  cpool->py_message_factory = message_factory::NewMessageFactory(
+      &PyMessageFactory_Type, cpool);
+  if (cpool->py_message_factory == NULL) {
+    Py_DECREF(cpool);
+    return NULL;
+  }
+
   return cpool;
 }
 
@@ -151,20 +149,14 @@ static PyObject* New(PyTypeObject* type,
 }
 
 static void Dealloc(PyDescriptorPool* self) {
-  typedef PyDescriptorPool::ClassesByMessageMap::iterator iterator;
   descriptor_pool_map.erase(self->pool);
-  for (iterator it = self->classes_by_descriptor->begin();
-       it != self->classes_by_descriptor->end(); ++it) {
-    Py_DECREF(it->second);
-  }
-  delete self->classes_by_descriptor;
+  Py_CLEAR(self->py_message_factory);
   for (hash_map<const void*, PyObject*>::iterator it =
            self->descriptor_options->begin();
        it != self->descriptor_options->end(); ++it) {
     Py_DECREF(it->second);
   }
   delete self->descriptor_options;
-  delete self->message_factory;
   delete self->database;
   delete self->pool;
   Py_TYPE(self)->tp_free(reinterpret_cast<PyObject*>(self));
@@ -188,35 +180,8 @@ PyObject* FindMessageByName(PyDescriptorPool* self, PyObject* arg) {
   return PyMessageDescriptor_FromDescriptor(message_descriptor);
 }
 
-// Add a message class to our database.
-int RegisterMessageClass(PyDescriptorPool* self,
-                         const Descriptor* message_descriptor,
-                         CMessageClass* message_class) {
-  Py_INCREF(message_class);
-  typedef PyDescriptorPool::ClassesByMessageMap::iterator iterator;
-  std::pair<iterator, bool> ret = self->classes_by_descriptor->insert(
-      std::make_pair(message_descriptor, message_class));
-  if (!ret.second) {
-    // Update case: DECREF the previous value.
-    Py_DECREF(ret.first->second);
-    ret.first->second = message_class;
-  }
-  return 0;
-}
 
-// Retrieve the message class added to our database.
-CMessageClass* GetMessageClass(PyDescriptorPool* self,
-                               const Descriptor* message_descriptor) {
-  typedef PyDescriptorPool::ClassesByMessageMap::iterator iterator;
-  iterator ret = self->classes_by_descriptor->find(message_descriptor);
-  if (ret == self->classes_by_descriptor->end()) {
-    PyErr_Format(PyExc_TypeError, "No message class registered for '%s'",
-                 message_descriptor->full_name().c_str());
-    return NULL;
-  } else {
-    return ret->second;
-  }
-}
+
 
 PyObject* FindFileByName(PyDescriptorPool* self, PyObject* arg) {
   Py_ssize_t name_size;
@@ -228,11 +193,9 @@ PyObject* FindFileByName(PyDescriptorPool* self, PyObject* arg) {
   const FileDescriptor* file_descriptor =
       self->pool->FindFileByName(string(name, name_size));
   if (file_descriptor == NULL) {
-    PyErr_Format(PyExc_KeyError, "Couldn't find file %.200s",
-                 name);
+    PyErr_Format(PyExc_KeyError, "Couldn't find file %.200s", name);
     return NULL;
   }
-
   return PyFileDescriptor_FromDescriptor(file_descriptor);
 }
 
diff --git a/python/google/protobuf/pyext/descriptor_pool.h b/python/google/protobuf/pyext/descriptor_pool.h
index 2a42c112..8de6c60b 100644
--- a/python/google/protobuf/pyext/descriptor_pool.h
+++ b/python/google/protobuf/pyext/descriptor_pool.h
@@ -38,10 +38,10 @@
 
 namespace google {
 namespace protobuf {
-class MessageFactory;
-
 namespace python {
 
+class PyMessageFactory;
+
 // The (meta) type of all Messages classes.
 struct CMessageClass;
 
@@ -69,20 +69,10 @@ typedef struct PyDescriptorPool {
   // This pointer is owned.
   const DescriptorDatabase* database;
 
-  // 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.
-  // Python references to classes are owned by this PyDescriptorPool.
-  typedef hash_map<const Descriptor*, CMessageClass*> ClassesByMessageMap;
-  ClassesByMessageMap* classes_by_descriptor;
+  // The preferred MessageFactory to be used by descriptors.
+  // TODO(amauryfa): Don't create the Factory from the DescriptorPool, but
+  // use the one passed while creating message classes. And remove this member.
+  PyMessageFactory* py_message_factory;
 
   // Cache the options for any kind of descriptor.
   // Descriptor pointers are owned by the DescriptorPool above.
@@ -100,19 +90,6 @@ namespace cdescriptor_pool {
 const Descriptor* FindMessageTypeByName(PyDescriptorPool* self,
                                         const string& name);
 
-// Registers a new Python class for the given message descriptor.
-// On error, returns -1 with a Python exception set.
-int RegisterMessageClass(PyDescriptorPool* self,
-                         const Descriptor* message_descriptor,
-                         CMessageClass* message_class);
-
-// Retrieves the Python class registered with the given message descriptor.
-//
-// Returns a *borrowed* reference if found, otherwise returns NULL with an
-// exception set.
-CMessageClass* GetMessageClass(PyDescriptorPool* self,
-                               const Descriptor* message_descriptor);
-
 // The functions below are also exposed as methods of the DescriptorPool type.
 
 // Looks up a message by name. Returns a PyMessageDescriptor corresponding to
diff --git a/python/google/protobuf/pyext/extension_dict.cc b/python/google/protobuf/pyext/extension_dict.cc
index 21bbb8c2..dbb7bca0 100644
--- a/python/google/protobuf/pyext/extension_dict.cc
+++ b/python/google/protobuf/pyext/extension_dict.cc
@@ -39,8 +39,8 @@
 #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/message_factory.h>
 #include <google/protobuf/pyext/repeated_composite_container.h>
 #include <google/protobuf/pyext/repeated_scalar_container.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
@@ -60,35 +60,6 @@ PyObject* len(ExtensionDict* self) {
 #endif
 }
 
-// TODO(tibell): Use VisitCompositeField.
-int ReleaseExtension(ExtensionDict* self,
-                     PyObject* extension,
-                     const FieldDescriptor* descriptor) {
-  if (descriptor->label() == FieldDescriptor::LABEL_REPEATED) {
-    if (descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-      if (repeated_composite_container::Release(
-              reinterpret_cast<RepeatedCompositeContainer*>(
-                  extension)) < 0) {
-        return -1;
-      }
-    } else {
-      if (repeated_scalar_container::Release(
-              reinterpret_cast<RepeatedScalarContainer*>(
-                  extension)) < 0) {
-        return -1;
-      }
-    }
-  } else if (descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-    if (cmessage::ReleaseSubMessage(
-            self->parent, descriptor,
-            reinterpret_cast<CMessage*>(extension)) < 0) {
-      return -1;
-    }
-  }
-
-  return 0;
-}
-
 PyObject* subscript(ExtensionDict* self, PyObject* key) {
   const FieldDescriptor* descriptor = cmessage::GetExtensionDescriptor(key);
   if (descriptor == NULL) {
@@ -130,8 +101,8 @@ PyObject* subscript(ExtensionDict* self, PyObject* key) {
 
   if (descriptor->label() == FieldDescriptor::LABEL_REPEATED) {
     if (descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-      CMessageClass* message_class = cdescriptor_pool::GetMessageClass(
-          cmessage::GetDescriptorPoolForMessage(self->parent),
+      CMessageClass* message_class = message_factory::GetMessageClass(
+          cmessage::GetFactoryForMessage(self->parent),
           descriptor->message_type());
       if (message_class == NULL) {
         return NULL;
@@ -183,47 +154,6 @@ int ass_subscript(ExtensionDict* self, PyObject* key, PyObject* value) {
   return 0;
 }
 
-PyObject* ClearExtension(ExtensionDict* self, PyObject* extension) {
-  const FieldDescriptor* descriptor =
-      cmessage::GetExtensionDescriptor(extension);
-  if (descriptor == NULL) {
-    return NULL;
-  }
-  PyObject* value = PyDict_GetItem(self->values, extension);
-  if (self->parent) {
-    if (value != NULL) {
-      if (ReleaseExtension(self, value, descriptor) < 0) {
-        return NULL;
-      }
-    }
-    if (ScopedPyObjectPtr(cmessage::ClearFieldByDescriptor(
-            self->parent, descriptor)) == NULL) {
-      return NULL;
-    }
-  }
-  if (PyDict_DelItem(self->values, extension) < 0) {
-    PyErr_Clear();
-  }
-  Py_RETURN_NONE;
-}
-
-PyObject* HasExtension(ExtensionDict* self, PyObject* extension) {
-  const FieldDescriptor* descriptor =
-      cmessage::GetExtensionDescriptor(extension);
-  if (descriptor == NULL) {
-    return NULL;
-  }
-  if (self->parent) {
-    return cmessage::HasFieldByDescriptor(self->parent, descriptor);
-  } else {
-    int exists = PyDict_Contains(self->values, extension);
-    if (exists < 0) {
-      return NULL;
-    }
-    return PyBool_FromLong(exists);
-  }
-}
-
 PyObject* _FindExtensionByName(ExtensionDict* self, PyObject* name) {
   ScopedPyObjectPtr extensions_by_name(PyObject_GetAttrString(
       reinterpret_cast<PyObject*>(self->parent), "_extensions_by_name"));
@@ -282,8 +212,6 @@ static PyMappingMethods MpMethods = {
 
 #define EDMETHOD(name, args, doc) { #name, (PyCFunction)name, args, doc }
 static PyMethodDef Methods[] = {
-  EDMETHOD(ClearExtension, METH_O, "Clears an extension from the object."),
-  EDMETHOD(HasExtension, METH_O, "Checks if the object has an extension."),
   EDMETHOD(_FindExtensionByName, METH_O,
            "Finds an extension by name."),
   EDMETHOD(_FindExtensionByNumber, METH_O,
diff --git a/python/google/protobuf/pyext/extension_dict.h b/python/google/protobuf/pyext/extension_dict.h
index 2456eda1..65b87862 100644
--- a/python/google/protobuf/pyext/extension_dict.h
+++ b/python/google/protobuf/pyext/extension_dict.h
@@ -86,49 +86,6 @@ namespace extension_dict {
 // Builds an Extensions dict for a specific message.
 ExtensionDict* NewExtensionDict(CMessage *parent);
 
-// Gets the number of extension values in this ExtensionDict as a python object.
-//
-// Returns a new reference.
-PyObject* len(ExtensionDict* self);
-
-// Releases extensions referenced outside this dictionary to keep outside
-// references alive.
-//
-// Returns 0 on success, -1 on failure.
-int ReleaseExtension(ExtensionDict* self,
-                     PyObject* extension,
-                     const FieldDescriptor* descriptor);
-
-// Gets an extension from the dict for the given extension descriptor.
-//
-// Returns a new reference.
-PyObject* subscript(ExtensionDict* self, PyObject* key);
-
-// Assigns a value to an extension in the dict. Can only be used for singular
-// simple types.
-//
-// Returns 0 on success, -1 on failure.
-int ass_subscript(ExtensionDict* self, PyObject* key, PyObject* value);
-
-// Clears an extension from the dict. Will release the extension if there
-// is still an external reference left to it.
-//
-// Returns None on success.
-PyObject* ClearExtension(ExtensionDict* self,
-                                       PyObject* extension);
-
-// Gets an extension from the dict given the extension name as opposed to
-// descriptor.
-//
-// Returns a new reference.
-PyObject* _FindExtensionByName(ExtensionDict* self, PyObject* name);
-
-// Gets an extension from the dict given the extension field number as
-// opposed to descriptor.
-//
-// Returns a new reference.
-PyObject* _FindExtensionByNumber(ExtensionDict* self, PyObject* number);
-
 }  // namespace extension_dict
 }  // namespace python
 }  // namespace protobuf
diff --git a/python/google/protobuf/pyext/map_container.cc b/python/google/protobuf/pyext/map_container.cc
index 0987b898..318c2e7c 100644
--- a/python/google/protobuf/pyext/map_container.cc
+++ b/python/google/protobuf/pyext/map_container.cc
@@ -42,7 +42,9 @@
 #include <google/protobuf/map_field.h>
 #include <google/protobuf/map.h>
 #include <google/protobuf/message.h>
+#include <google/protobuf/pyext/message_factory.h>
 #include <google/protobuf/pyext/message.h>
+#include <google/protobuf/pyext/repeated_composite_container.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
 
 #if PY_MAJOR_VERSION >= 3
@@ -328,6 +330,15 @@ PyObject* Clear(PyObject* _self) {
   Py_RETURN_NONE;
 }
 
+PyObject* GetEntryClass(PyObject* _self) {
+  MapContainer* self = GetMap(_self);
+  CMessageClass* message_class = message_factory::GetMessageClass(
+      cmessage::GetFactoryForMessage(self->parent),
+      self->parent_field_descriptor->message_type());
+  Py_XINCREF(message_class);
+  return reinterpret_cast<PyObject*>(message_class);
+}
+
 PyObject* MapReflectionFriend::Contains(PyObject* _self, PyObject* key) {
   MapContainer* self = GetMap(_self);
 
@@ -400,12 +411,7 @@ PyObject *NewScalarMapContainer(
     return NULL;
   }
 
-#if PY_MAJOR_VERSION >= 3
-  ScopedPyObjectPtr obj(PyType_GenericAlloc(
-        reinterpret_cast<PyTypeObject *>(ScalarMapContainer_Type), 0));
-#else
-  ScopedPyObjectPtr obj(PyType_GenericAlloc(&ScalarMapContainer_Type, 0));
-#endif
+  ScopedPyObjectPtr obj(PyType_GenericAlloc(ScalarMapContainer_Type, 0));
   if (obj.get() == NULL) {
     return PyErr_Format(PyExc_RuntimeError,
                         "Could not allocate new container.");
@@ -527,6 +533,8 @@ static PyMethodDef ScalarMapMethods[] = {
     "Removes all elements from the map." },
   { "get", ScalarMapGet, METH_VARARGS,
     "Gets the value for the given key if present, or otherwise a default" },
+  { "GetEntryClass", (PyCFunction)GetEntryClass, METH_NOARGS,
+    "Return the class used to build Entries of (key, value) pairs." },
   /*
   { "__deepcopy__", (PyCFunction)DeepCopy, METH_VARARGS,
     "Makes a deep copy of the class." },
@@ -536,6 +544,7 @@ static PyMethodDef ScalarMapMethods[] = {
   {NULL, NULL},
 };
 
+PyTypeObject *ScalarMapContainer_Type;
 #if PY_MAJOR_VERSION >= 3
   static PyType_Slot ScalarMapContainer_Type_slots[] = {
       {Py_tp_dealloc, (void *)ScalarMapDealloc},
@@ -554,7 +563,6 @@ static PyMethodDef ScalarMapMethods[] = {
       Py_TPFLAGS_DEFAULT,
       ScalarMapContainer_Type_slots
   };
-  PyObject *ScalarMapContainer_Type;
 #else
   static PyMappingMethods ScalarMapMappingMethods = {
     MapReflectionFriend::Length,             // mp_length
@@ -562,7 +570,7 @@ static PyMethodDef ScalarMapMethods[] = {
     MapReflectionFriend::ScalarMapSetItem,   // mp_ass_subscript
   };
 
-  PyTypeObject ScalarMapContainer_Type = {
+  PyTypeObject _ScalarMapContainer_Type = {
     PyVarObject_HEAD_INIT(&PyType_Type, 0)
     FULL_MODULE_NAME ".ScalarMapContainer",  //  tp_name
     sizeof(MapContainer),                //  tp_basicsize
@@ -643,12 +651,7 @@ PyObject* NewMessageMapContainer(
     return NULL;
   }
 
-#if PY_MAJOR_VERSION >= 3
-  PyObject* obj = PyType_GenericAlloc(
-        reinterpret_cast<PyTypeObject *>(MessageMapContainer_Type), 0);
-#else
-  PyObject* obj = PyType_GenericAlloc(&MessageMapContainer_Type, 0);
-#endif
+  PyObject* obj = PyType_GenericAlloc(MessageMapContainer_Type, 0);
   if (obj == NULL) {
     return PyErr_Format(PyExc_RuntimeError,
                         "Could not allocate new container.");
@@ -780,6 +783,8 @@ static PyMethodDef MessageMapMethods[] = {
     "Gets the value for the given key if present, or otherwise a default" },
   { "get_or_create", MapReflectionFriend::MessageMapGetItem, METH_O,
     "Alias for getitem, useful to make explicit that the map is mutated." },
+  { "GetEntryClass", (PyCFunction)GetEntryClass, METH_NOARGS,
+    "Return the class used to build Entries of (key, value) pairs." },
   /*
   { "__deepcopy__", (PyCFunction)DeepCopy, METH_VARARGS,
     "Makes a deep copy of the class." },
@@ -789,6 +794,7 @@ static PyMethodDef MessageMapMethods[] = {
   {NULL, NULL},
 };
 
+PyTypeObject *MessageMapContainer_Type;
 #if PY_MAJOR_VERSION >= 3
   static PyType_Slot MessageMapContainer_Type_slots[] = {
       {Py_tp_dealloc, (void *)MessageMapDealloc},
@@ -807,8 +813,6 @@ static PyMethodDef MessageMapMethods[] = {
       Py_TPFLAGS_DEFAULT,
       MessageMapContainer_Type_slots
   };
-
-  PyObject *MessageMapContainer_Type;
 #else
   static PyMappingMethods MessageMapMappingMethods = {
     MapReflectionFriend::Length,              // mp_length
@@ -816,7 +820,7 @@ static PyMethodDef MessageMapMethods[] = {
     MapReflectionFriend::MessageMapSetItem,   // mp_ass_subscript
   };
 
-  PyTypeObject MessageMapContainer_Type = {
+  PyTypeObject _MessageMapContainer_Type = {
     PyVarObject_HEAD_INIT(&PyType_Type, 0)
     FULL_MODULE_NAME ".MessageMapContainer",  //  tp_name
     sizeof(MessageMapContainer),         //  tp_basicsize
@@ -965,6 +969,63 @@ PyTypeObject MapIterator_Type = {
   0,                                   //  tp_init
 };
 
+bool InitMapContainers() {
+  // ScalarMapContainer_Type derives from our MutableMapping type.
+  ScopedPyObjectPtr containers(PyImport_ImportModule(
+      "google.protobuf.internal.containers"));
+  if (containers == NULL) {
+    return false;
+  }
+
+  ScopedPyObjectPtr mutable_mapping(
+      PyObject_GetAttrString(containers.get(), "MutableMapping"));
+  if (mutable_mapping == NULL) {
+    return false;
+  }
+
+  if (!PyObject_TypeCheck(mutable_mapping.get(), &PyType_Type)) {
+    return false;
+  }
+
+  Py_INCREF(mutable_mapping.get());
+#if PY_MAJOR_VERSION >= 3
+  PyObject* bases = PyTuple_New(1);
+  PyTuple_SET_ITEM(bases, 0, mutable_mapping.get());
+
+  ScalarMapContainer_Type = reinterpret_cast<PyTypeObject*>(
+      PyType_FromSpecWithBases(&ScalarMapContainer_Type_spec, bases));
+#else
+  _ScalarMapContainer_Type.tp_base =
+      reinterpret_cast<PyTypeObject*>(mutable_mapping.get());
+
+  if (PyType_Ready(&_ScalarMapContainer_Type) < 0) {
+    return false;
+  }
+
+  ScalarMapContainer_Type = &_ScalarMapContainer_Type;
+#endif
+
+  if (PyType_Ready(&MapIterator_Type) < 0) {
+    return false;
+  }
+
+#if PY_MAJOR_VERSION >= 3
+  MessageMapContainer_Type = reinterpret_cast<PyTypeObject*>(
+      PyType_FromSpecWithBases(&MessageMapContainer_Type_spec, bases));
+#else
+  Py_INCREF(mutable_mapping.get());
+  _MessageMapContainer_Type.tp_base =
+      reinterpret_cast<PyTypeObject*>(mutable_mapping.get());
+
+  if (PyType_Ready(&_MessageMapContainer_Type) < 0) {
+    return false;
+  }
+
+  MessageMapContainer_Type = &_MessageMapContainer_Type;
+#endif
+  return true;
+}
+
 }  // namespace python
 }  // namespace protobuf
 }  // namespace google
diff --git a/python/google/protobuf/pyext/map_container.h b/python/google/protobuf/pyext/map_container.h
index fbd6713f..615657b0 100644
--- a/python/google/protobuf/pyext/map_container.h
+++ b/python/google/protobuf/pyext/map_container.h
@@ -112,16 +112,10 @@ struct MessageMapContainer : public MapContainer {
   PyObject* message_dict;
 };
 
-#if PY_MAJOR_VERSION >= 3
-  extern PyObject *MessageMapContainer_Type;
-  extern PyType_Spec MessageMapContainer_Type_spec;
-  extern PyObject *ScalarMapContainer_Type;
-  extern PyType_Spec ScalarMapContainer_Type_spec;
-#else
-  extern PyTypeObject MessageMapContainer_Type;
-  extern PyTypeObject ScalarMapContainer_Type;
-#endif
+bool InitMapContainers();
 
+extern PyTypeObject* MessageMapContainer_Type;
+extern PyTypeObject* ScalarMapContainer_Type;
 extern PyTypeObject MapIterator_Type;  // Both map types use the same iterator.
 
 // Builds a MapContainer object, from a parent message and a
diff --git a/python/google/protobuf/pyext/message.cc b/python/google/protobuf/pyext/message.cc
index 5535338d..1b325469 100644
--- a/python/google/protobuf/pyext/message.cc
+++ b/python/google/protobuf/pyext/message.cc
@@ -63,6 +63,7 @@
 #include <google/protobuf/pyext/repeated_composite_container.h>
 #include <google/protobuf/pyext/repeated_scalar_container.h>
 #include <google/protobuf/pyext/map_container.h>
+#include <google/protobuf/pyext/message_factory.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
 #include <google/protobuf/stubs/strutil.h>
 
@@ -244,6 +245,12 @@ static PyObject* New(PyTypeObject* type,
     return NULL;
   }
 
+  // Messages have no __dict__
+  ScopedPyObjectPtr slots(PyTuple_New(0));
+  if (PyDict_SetItemString(dict, "__slots__", slots.get()) < 0) {
+    return NULL;
+  }
+
   // Build the arguments to the base metaclass.
   // We change the __bases__ classes.
   ScopedPyObjectPtr new_args;
@@ -300,16 +307,19 @@ static PyObject* New(PyTypeObject* type,
   newtype->message_descriptor = descriptor;
   // TODO(amauryfa): Don't always use the canonical pool of the descriptor,
   // use the MessageFactory optionally passed in the class dict.
-  newtype->py_descriptor_pool = GetDescriptorPool_FromPool(
-      descriptor->file()->pool());
-  if (newtype->py_descriptor_pool == NULL) {
+  PyDescriptorPool* py_descriptor_pool =
+      GetDescriptorPool_FromPool(descriptor->file()->pool());
+  if (py_descriptor_pool == NULL) {
     return NULL;
   }
-  Py_INCREF(newtype->py_descriptor_pool);
+  newtype->py_message_factory = py_descriptor_pool->py_message_factory;
+  Py_INCREF(newtype->py_message_factory);
 
-  // Add the message to the DescriptorPool.
-  if (cdescriptor_pool::RegisterMessageClass(newtype->py_descriptor_pool,
-                                             descriptor, newtype) < 0) {
+  // Register the message in the MessageFactory.
+  // TODO(amauryfa): Move this call to MessageFactory.GetPrototype() when the
+  // MessageFactory is fully implemented in C++.
+  if (message_factory::RegisterMessageClass(newtype->py_message_factory,
+                                            descriptor, newtype) < 0) {
     return NULL;
   }
 
@@ -321,8 +331,8 @@ static PyObject* New(PyTypeObject* type,
 }
 
 static void Dealloc(CMessageClass *self) {
-  Py_DECREF(self->py_message_descriptor);
-  Py_DECREF(self->py_descriptor_pool);
+  Py_XDECREF(self->py_message_descriptor);
+  Py_XDECREF(self->py_message_factory);
   Py_TYPE(self)->tp_free(reinterpret_cast<PyObject*>(self));
 }
 
@@ -752,15 +762,9 @@ bool CheckFieldBelongsToMessage(const FieldDescriptor* field_descriptor,
 
 namespace cmessage {
 
-PyDescriptorPool* GetDescriptorPoolForMessage(CMessage* message) {
-  // No need to check the type: the type of instances of CMessage is always
-  // an instance of CMessageClass. Let's prove it with a debug-only check.
+PyMessageFactory* GetFactoryForMessage(CMessage* message) {
   GOOGLE_DCHECK(PyObject_TypeCheck(message, &CMessage_Type));
-  return reinterpret_cast<CMessageClass*>(Py_TYPE(message))->py_descriptor_pool;
-}
-
-MessageFactory* GetFactoryForMessage(CMessage* message) {
-  return GetDescriptorPoolForMessage(message)->message_factory;
+  return reinterpret_cast<CMessageClass*>(Py_TYPE(message))->py_message_factory;
 }
 
 static int MaybeReleaseOverlappingOneofField(
@@ -813,7 +817,8 @@ static Message* GetMutableMessage(
     return NULL;
   }
   return reflection->MutableMessage(
-      parent_message, parent_field, GetFactoryForMessage(parent));
+      parent_message, parent_field,
+      GetFactoryForMessage(parent)->message_factory);
 }
 
 struct FixupMessageReference : public ChildVisitor {
@@ -1172,6 +1177,8 @@ int InitAttributes(CMessage* self, PyObject* args, PyObject* kwargs) {
       }
       CMessage* cmessage = reinterpret_cast<CMessage*>(message.get());
       if (PyDict_Check(value)) {
+        // Make the message exist even if the dict is empty.
+        AssureWritable(cmessage);
         if (InitAttributes(cmessage, NULL, value) < 0) {
           return -1;
         }
@@ -1231,7 +1238,7 @@ static PyObject* New(PyTypeObject* cls,
   if (message_descriptor == NULL) {
     return NULL;
   }
-  const Message* default_message = type->py_descriptor_pool->message_factory
+  const Message* default_message = type->py_message_factory->message_factory
                                    ->GetPrototype(message_descriptor);
   if (default_message == NULL) {
     PyErr_SetString(PyExc_TypeError, message_descriptor->full_name().c_str());
@@ -1292,6 +1299,9 @@ struct ClearWeakReferences : public ChildVisitor {
 };
 
 static void Dealloc(CMessage* self) {
+  if (self->weakreflist) {
+    PyObject_ClearWeakRefs(reinterpret_cast<PyObject*>(self));
+  }
   // Null out all weak references from children to this message.
   GOOGLE_CHECK_EQ(0, ForEachCompositeField(self, ClearWeakReferences()));
   if (self->extensions) {
@@ -1459,18 +1469,20 @@ PyObject* HasField(CMessage* self, PyObject* arg) {
 }
 
 PyObject* ClearExtension(CMessage* self, PyObject* extension) {
+  const FieldDescriptor* descriptor = GetExtensionDescriptor(extension);
+  if (descriptor == NULL) {
+    return NULL;
+  }
   if (self->extensions != NULL) {
-    return extension_dict::ClearExtension(self->extensions, extension);
-  } else {
-    const FieldDescriptor* descriptor = GetExtensionDescriptor(extension);
-    if (descriptor == NULL) {
-      return NULL;
-    }
-    if (ScopedPyObjectPtr(ClearFieldByDescriptor(self, descriptor)) == NULL) {
-      return NULL;
+    PyObject* value = PyDict_GetItem(self->extensions->values, extension);
+    if (value != NULL) {
+      if (InternalReleaseFieldByDescriptor(self, descriptor, value) < 0) {
+        return NULL;
+      }
+      PyDict_DelItem(self->extensions->values, extension);
     }
   }
-  Py_RETURN_NONE;
+  return ClearFieldByDescriptor(self, descriptor);
 }
 
 PyObject* HasExtension(CMessage* self, PyObject* extension) {
@@ -1556,7 +1568,7 @@ int SetOwner(CMessage* self, const shared_ptr<Message>& new_owner) {
 Message* ReleaseMessage(CMessage* self,
                         const Descriptor* descriptor,
                         const FieldDescriptor* field_descriptor) {
-  MessageFactory* message_factory = GetFactoryForMessage(self);
+  MessageFactory* message_factory = GetFactoryForMessage(self)->message_factory;
   Message* released_message = self->message->GetReflection()->ReleaseMessage(
       self->message, field_descriptor, message_factory);
   // ReleaseMessage will return NULL which differs from
@@ -1624,12 +1636,19 @@ int InternalReleaseFieldByDescriptor(
 
 PyObject* ClearFieldByDescriptor(
     CMessage* self,
-    const FieldDescriptor* descriptor) {
-  if (!CheckFieldBelongsToMessage(descriptor, self->message)) {
+    const FieldDescriptor* field_descriptor) {
+  if (!CheckFieldBelongsToMessage(field_descriptor, self->message)) {
     return NULL;
   }
   AssureWritable(self);
-  self->message->GetReflection()->ClearField(self->message, descriptor);
+  Message* message = self->message;
+  message->GetReflection()->ClearField(message, field_descriptor);
+  if (field_descriptor->cpp_type() == FieldDescriptor::CPPTYPE_ENUM &&
+      !message->GetReflection()->SupportsUnknownEnumValues()) {
+    UnknownFieldSet* unknown_field_set =
+        message->GetReflection()->MutableUnknownFields(message);
+    unknown_field_set->DeleteByNumber(field_descriptor->number());
+  }
   Py_RETURN_NONE;
 }
 
@@ -1665,27 +1684,17 @@ PyObject* ClearField(CMessage* self, PyObject* arg) {
     arg = arg_in_oneof.get();
   }
 
-  PyObject* composite_field = self->composite_fields ?
-      PyDict_GetItem(self->composite_fields, arg) : NULL;
-
-  // Only release the field if there's a possibility that there are
-  // references to it.
-  if (composite_field != NULL) {
-    if (InternalReleaseFieldByDescriptor(self, field_descriptor,
-                                         composite_field) < 0) {
-      return NULL;
+  // Release the field if it exists in the dict of composite fields.
+  if (self->composite_fields) {
+    PyObject* value = PyDict_GetItem(self->composite_fields, arg);
+    if (value != NULL) {
+      if (InternalReleaseFieldByDescriptor(self, field_descriptor, value) < 0) {
+        return NULL;
+      }
+      PyDict_DelItem(self->composite_fields, arg);
     }
-    PyDict_DelItem(self->composite_fields, arg);
-  }
-  message->GetReflection()->ClearField(message, field_descriptor);
-  if (field_descriptor->cpp_type() == FieldDescriptor::CPPTYPE_ENUM &&
-      !message->GetReflection()->SupportsUnknownEnumValues()) {
-    UnknownFieldSet* unknown_field_set =
-        message->GetReflection()->MutableUnknownFields(message);
-    unknown_field_set->DeleteByNumber(field_descriptor->number());
   }
-
-  Py_RETURN_NONE;
+  return ClearFieldByDescriptor(self, field_descriptor);
 }
 
 PyObject* Clear(CMessage* self) {
@@ -1927,8 +1936,8 @@ static PyObject* MergeFromString(CMessage* self, PyObject* arg) {
   if (allow_oversize_protos) {
     input.SetTotalBytesLimit(INT_MAX, INT_MAX);
   }
-  PyDescriptorPool* pool = GetDescriptorPoolForMessage(self);
-  input.SetExtensionRegistry(pool->pool, pool->message_factory);
+  PyMessageFactory* factory = GetFactoryForMessage(self);
+  input.SetExtensionRegistry(factory->pool->pool, factory->message_factory);
   bool success = self->message->MergePartialFromCodedStream(&input);
   if (success) {
     return PyInt_FromLong(input.CurrentPosition());
@@ -2108,8 +2117,8 @@ static PyObject* ListFields(CMessage* self) {
       // is no message class and we cannot retrieve the value.
       // TODO(amauryfa): consider building the class on the fly!
       if (fields[i]->message_type() != NULL &&
-          cdescriptor_pool::GetMessageClass(
-              GetDescriptorPoolForMessage(self),
+          message_factory::GetMessageClass(
+              GetFactoryForMessage(self),
               fields[i]->message_type()) == NULL) {
         PyErr_Clear();
         continue;
@@ -2306,12 +2315,12 @@ PyObject* InternalGetScalar(const Message* message,
 PyObject* InternalGetSubMessage(
     CMessage* self, const FieldDescriptor* field_descriptor) {
   const Reflection* reflection = self->message->GetReflection();
-  PyDescriptorPool* pool = GetDescriptorPoolForMessage(self);
+  PyMessageFactory* factory = GetFactoryForMessage(self);
   const Message& sub_message = reflection->GetMessage(
-      *self->message, field_descriptor, pool->message_factory);
+      *self->message, field_descriptor, factory->message_factory);
 
-  CMessageClass* message_class = cdescriptor_pool::GetMessageClass(
-      pool, field_descriptor->message_type());
+  CMessageClass* message_class = message_factory::GetMessageClass(
+      factory, field_descriptor->message_type());
   if (message_class == NULL) {
     return NULL;
   }
@@ -2656,8 +2665,8 @@ PyObject* GetAttr(CMessage* self, PyObject* name) {
     const Descriptor* entry_type = field_descriptor->message_type();
     const FieldDescriptor* value_type = entry_type->FindFieldByName("value");
     if (value_type->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-      CMessageClass* value_class = cdescriptor_pool::GetMessageClass(
-          GetDescriptorPoolForMessage(self), value_type->message_type());
+      CMessageClass* value_class = message_factory::GetMessageClass(
+          GetFactoryForMessage(self), value_type->message_type());
       if (value_class == NULL) {
         return NULL;
       }
@@ -2679,8 +2688,8 @@ PyObject* GetAttr(CMessage* self, PyObject* name) {
   if (field_descriptor->label() == FieldDescriptor::LABEL_REPEATED) {
     PyObject* py_container = NULL;
     if (field_descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-      CMessageClass* message_class = cdescriptor_pool::GetMessageClass(
-          GetDescriptorPoolForMessage(self), field_descriptor->message_type());
+      CMessageClass* message_class = message_factory::GetMessageClass(
+          GetFactoryForMessage(self), field_descriptor->message_type());
       if (message_class == NULL) {
         return NULL;
       }
@@ -2775,7 +2784,7 @@ PyTypeObject CMessage_Type = {
   0,                                   //  tp_traverse
   0,                                   //  tp_clear
   (richcmpfunc)cmessage::RichCompare,  //  tp_richcompare
-  0,                                   //  tp_weaklistoffset
+  offsetof(CMessage, weakreflist),     //  tp_weaklistoffset
   0,                                   //  tp_iter
   0,                                   //  tp_iternext
   cmessage::Methods,                   //  tp_methods
@@ -2863,6 +2872,11 @@ bool InitProto2MessageModule(PyObject *m) {
     return false;
   }
 
+  // Initialize types and globals in message_factory.cc
+  if (!InitMessageFactory()) {
+    return false;
+  }
+
   // Initialize constants defined in this file.
   InitGlobals();
 
@@ -2944,69 +2958,15 @@ bool InitProto2MessageModule(PyObject *m) {
   }
 
   // Initialize Map container types.
-  {
-    // ScalarMapContainer_Type derives from our MutableMapping type.
-    ScopedPyObjectPtr containers(PyImport_ImportModule(
-        "google.protobuf.internal.containers"));
-    if (containers == NULL) {
-      return false;
-    }
-
-    ScopedPyObjectPtr mutable_mapping(
-        PyObject_GetAttrString(containers.get(), "MutableMapping"));
-    if (mutable_mapping == NULL) {
-      return false;
-    }
-
-    if (!PyObject_TypeCheck(mutable_mapping.get(), &PyType_Type)) {
-      return false;
-    }
-
-    Py_INCREF(mutable_mapping.get());
-#if PY_MAJOR_VERSION >= 3
-    PyObject* bases = PyTuple_New(1);
-    PyTuple_SET_ITEM(bases, 0, mutable_mapping.get());
-
-    ScalarMapContainer_Type = 
-        PyType_FromSpecWithBases(&ScalarMapContainer_Type_spec, bases);
-    PyModule_AddObject(m, "ScalarMapContainer", ScalarMapContainer_Type);
-#else
-    ScalarMapContainer_Type.tp_base =
-        reinterpret_cast<PyTypeObject*>(mutable_mapping.get());
-
-    if (PyType_Ready(&ScalarMapContainer_Type) < 0) {
-      return false;
-    }
-
-    PyModule_AddObject(m, "ScalarMapContainer",
-                       reinterpret_cast<PyObject*>(&ScalarMapContainer_Type));
-#endif
-
-    if (PyType_Ready(&MapIterator_Type) < 0) {
-      return false;
-    }
-
-    PyModule_AddObject(m, "MapIterator",
-                       reinterpret_cast<PyObject*>(&MapIterator_Type));
-
-
-#if PY_MAJOR_VERSION >= 3
-    MessageMapContainer_Type = 
-        PyType_FromSpecWithBases(&MessageMapContainer_Type_spec, bases);
-    PyModule_AddObject(m, "MessageMapContainer", MessageMapContainer_Type);
-#else
-    Py_INCREF(mutable_mapping.get());
-    MessageMapContainer_Type.tp_base =
-        reinterpret_cast<PyTypeObject*>(mutable_mapping.get());
-
-    if (PyType_Ready(&MessageMapContainer_Type) < 0) {
-      return false;
-    }
-
-    PyModule_AddObject(m, "MessageMapContainer",
-                       reinterpret_cast<PyObject*>(&MessageMapContainer_Type));
-#endif
+  if (!InitMapContainers()) {
+    return false;
   }
+  PyModule_AddObject(m, "ScalarMapContainer",
+                     reinterpret_cast<PyObject*>(ScalarMapContainer_Type));
+  PyModule_AddObject(m, "MessageMapContainer",
+                     reinterpret_cast<PyObject*>(MessageMapContainer_Type));
+  PyModule_AddObject(m, "MapIterator",
+                     reinterpret_cast<PyObject*>(&MapIterator_Type));
 
   if (PyType_Ready(&ExtensionDict_Type) < 0) {
     return false;
diff --git a/python/google/protobuf/pyext/message.h b/python/google/protobuf/pyext/message.h
index c44a2ae2..1550724c 100644
--- a/python/google/protobuf/pyext/message.h
+++ b/python/google/protobuf/pyext/message.h
@@ -62,7 +62,7 @@ using internal::shared_ptr;
 namespace python {
 
 struct ExtensionDict;
-struct PyDescriptorPool;
+struct PyMessageFactory;
 
 typedef struct CMessage {
   PyObject_HEAD;
@@ -112,6 +112,9 @@ typedef struct CMessage {
   // Similar to composite_fields, acting as a cache, but also contains the
   // required extension dict logic.
   ExtensionDict* extensions;
+
+  // Implements the "weakref" protocol for this object.
+  PyObject* weakreflist;
 } CMessage;
 
 extern PyTypeObject CMessage_Type;
@@ -132,14 +135,11 @@ struct CMessageClass {
   // Owned reference, used to keep the pointer above alive.
   PyObject* py_message_descriptor;
 
-  // The Python DescriptorPool used to create the class. It is needed to resolve
+  // The Python MessageFactory used to create the class. It is needed to resolve
   // fields descriptors, including extensions fields; its C++ MessageFactory is
   // used to instantiate submessages.
-  // This can be different from DESCRIPTOR.file.pool, in the case of a custom
-  // DescriptorPool which defines new extensions.
-  // We own the reference, because it's important to keep the descriptors and
-  // factory alive.
-  PyDescriptorPool* py_descriptor_pool;
+  // We own the reference, because it's important to keep the factory alive.
+  PyMessageFactory* py_message_factory;
 
   PyObject* AsPyObject() {
     return reinterpret_cast<PyObject*>(this);
@@ -154,14 +154,6 @@ namespace cmessage {
 // The caller must fill self->message, self->owner and eventually self->parent.
 CMessage* NewEmptyMessage(CMessageClass* type);
 
-// Release a submessage from its proto tree, making it a new top-level messgae.
-// A new message will be created if this is a read-only default instance.
-//
-// Corresponds to reflection api method ReleaseMessage.
-int ReleaseSubMessage(CMessage* self,
-                      const FieldDescriptor* field_descriptor,
-                      CMessage* child_cmessage);
-
 // Retrieves the C++ descriptor of a Python Extension descriptor.
 // On error, return NULL with an exception set.
 const FieldDescriptor* GetExtensionDescriptor(PyObject* extension);
@@ -262,14 +254,13 @@ int SetOwner(CMessage* self, const shared_ptr<Message>& new_owner);
 
 int AssureWritable(CMessage* self);
 
-// Returns the "best" DescriptorPool for the given message.
-// This is often equivalent to message.DESCRIPTOR.pool, but not always, when
-// the message class was created from a MessageFactory using a custom pool which
-// uses the generated pool as an underlay.
+// Returns the message factory for the given message.
+// This is equivalent to message.MESSAGE_FACTORY
 //
-// The returned pool is suitable for finding fields and building submessages,
+// The returned factory is suitable for finding fields and building submessages,
 // even in the case of extensions.
-PyDescriptorPool* GetDescriptorPoolForMessage(CMessage* message);
+// Returns a *borrowed* reference, and never fails because we pass a CMessage.
+PyMessageFactory* GetFactoryForMessage(CMessage* message);
 
 PyObject* SetAllowOversizeProtos(PyObject* m, PyObject* arg);
 
diff --git a/python/google/protobuf/pyext/message_factory.cc b/python/google/protobuf/pyext/message_factory.cc
new file mode 100644
index 00000000..2ad89022
--- /dev/null
+++ b/python/google/protobuf/pyext/message_factory.cc
@@ -0,0 +1,214 @@
+// 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.
+
+#include <Python.h>
+
+#include <google/protobuf/dynamic_message.h>
+#include <google/protobuf/pyext/descriptor.h>
+#include <google/protobuf/pyext/message.h>
+#include <google/protobuf/pyext/message_factory.h>
+#include <google/protobuf/pyext/scoped_pyobject_ptr.h>
+
+#if PY_MAJOR_VERSION >= 3
+  #if PY_VERSION_HEX < 0x03030000
+    #error "Python 3.0 - 3.2 are not supported."
+  #endif
+  #define PyString_AsStringAndSize(ob, charpp, sizep) \
+    (PyUnicode_Check(ob)? \
+       ((*(charpp) = PyUnicode_AsUTF8AndSize(ob, (sizep))) == NULL? -1: 0): \
+       PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
+#endif
+
+namespace google {
+namespace protobuf {
+namespace python {
+
+namespace message_factory {
+
+PyMessageFactory* NewMessageFactory(PyTypeObject* type, PyDescriptorPool* pool) {
+  PyMessageFactory* factory = reinterpret_cast<PyMessageFactory*>(
+      PyType_GenericAlloc(type, 0));
+  if (factory == NULL) {
+    return NULL;
+  }
+
+  DynamicMessageFactory* message_factory = new DynamicMessageFactory();
+  // This option might be the default some day.
+  message_factory->SetDelegateToGeneratedFactory(true);
+  factory->message_factory = message_factory;
+
+  factory->pool = pool;
+  // TODO(amauryfa): When the MessageFactory is not created from the
+  // DescriptorPool this reference should be owned, not borrowed.
+  // Py_INCREF(pool);
+
+  factory->classes_by_descriptor = new PyMessageFactory::ClassesByMessageMap();
+
+  return factory;
+}
+
+PyObject* New(PyTypeObject* type, PyObject* args, PyObject* kwargs) {
+  static char* kwlist[] = {"pool", 0};
+  PyObject* pool = NULL;
+  if (!PyArg_ParseTupleAndKeywords(args, kwargs, "|O", kwlist, &pool)) {
+    return NULL;
+  }
+  ScopedPyObjectPtr owned_pool;
+  if (pool == NULL || pool == Py_None) {
+    owned_pool.reset(PyObject_CallFunction(
+        reinterpret_cast<PyObject*>(&PyDescriptorPool_Type), NULL));
+    if (owned_pool == NULL) {
+      return NULL;
+    }
+    pool = owned_pool.get();
+  } else {
+    if (!PyObject_TypeCheck(pool, &PyDescriptorPool_Type)) {
+      PyErr_Format(PyExc_TypeError, "Expected a DescriptorPool, got %s",
+                   pool->ob_type->tp_name);
+      return NULL;
+    }
+  }
+
+  return reinterpret_cast<PyObject*>(
+      NewMessageFactory(type, reinterpret_cast<PyDescriptorPool*>(pool)));
+}
+
+static void Dealloc(PyMessageFactory* self) {
+  // TODO(amauryfa): When the MessageFactory is not created from the
+  // DescriptorPool this reference should be owned, not borrowed.
+  // Py_CLEAR(self->pool);
+  typedef PyMessageFactory::ClassesByMessageMap::iterator iterator;
+  for (iterator it = self->classes_by_descriptor->begin();
+       it != self->classes_by_descriptor->end(); ++it) {
+    Py_DECREF(it->second);
+  }
+  delete self->classes_by_descriptor;
+  delete self->message_factory;
+  Py_TYPE(self)->tp_free(reinterpret_cast<PyObject*>(self));
+}
+
+// Add a message class to our database.
+int RegisterMessageClass(PyMessageFactory* self,
+                         const Descriptor* message_descriptor,
+                         CMessageClass* message_class) {
+  Py_INCREF(message_class);
+  typedef PyMessageFactory::ClassesByMessageMap::iterator iterator;
+  std::pair<iterator, bool> ret = self->classes_by_descriptor->insert(
+      std::make_pair(message_descriptor, message_class));
+  if (!ret.second) {
+    // Update case: DECREF the previous value.
+    Py_DECREF(ret.first->second);
+    ret.first->second = message_class;
+  }
+  return 0;
+}
+
+// Retrieve the message class added to our database.
+CMessageClass* GetMessageClass(PyMessageFactory* self,
+                               const Descriptor* message_descriptor) {
+  typedef PyMessageFactory::ClassesByMessageMap::iterator iterator;
+  iterator ret = self->classes_by_descriptor->find(message_descriptor);
+  if (ret == self->classes_by_descriptor->end()) {
+    PyErr_Format(PyExc_TypeError, "No message class registered for '%s'",
+                 message_descriptor->full_name().c_str());
+    return NULL;
+  } else {
+    return ret->second;
+  }
+}
+
+static PyMethodDef Methods[] = {
+    {NULL}};
+
+static PyObject* GetPool(PyMessageFactory* self, void* closure) {
+  Py_INCREF(self->pool);
+  return reinterpret_cast<PyObject*>(self->pool);
+}
+
+static PyGetSetDef Getters[] = {
+    {"pool", (getter)GetPool, NULL, "DescriptorPool"},
+    {NULL}
+};
+
+}  // namespace message_factory
+
+PyTypeObject PyMessageFactory_Type = {
+    PyVarObject_HEAD_INIT(&PyType_Type, 0) FULL_MODULE_NAME
+    ".MessageFactory",                        // tp_name
+    sizeof(PyMessageFactory),                 // tp_basicsize
+    0,                                        // tp_itemsize
+    (destructor)message_factory::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
+    "A static Message Factory",               // tp_doc
+    0,                                        // tp_traverse
+    0,                                        // tp_clear
+    0,                                        // tp_richcompare
+    0,                                        // tp_weaklistoffset
+    0,                                        // tp_iter
+    0,                                        // tp_iternext
+    message_factory::Methods,                 // tp_methods
+    0,                                        // tp_members
+    message_factory::Getters,                 // 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_factory::New,                     // tp_new
+    PyObject_Del,                             // tp_free
+};
+
+bool InitMessageFactory() {
+  if (PyType_Ready(&PyMessageFactory_Type) < 0) {
+    return false;
+  }
+
+  return true;
+}
+
+}  // namespace python
+}  // namespace protobuf
+}  // namespace google
diff --git a/python/google/protobuf/pyext/message_factory.h b/python/google/protobuf/pyext/message_factory.h
new file mode 100644
index 00000000..07cccbfb
--- /dev/null
+++ b/python/google/protobuf/pyext/message_factory.h
@@ -0,0 +1,103 @@
+// 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.
+
+#ifndef GOOGLE_PROTOBUF_PYTHON_CPP_MESSAGE_FACTORY_H__
+#define GOOGLE_PROTOBUF_PYTHON_CPP_MESSAGE_FACTORY_H__
+
+#include <Python.h>
+
+#include <google/protobuf/stubs/hash.h>
+#include <google/protobuf/descriptor.h>
+#include <google/protobuf/pyext/descriptor_pool.h>
+
+namespace google {
+namespace protobuf {
+class MessageFactory;
+
+namespace python {
+
+// The (meta) type of all Messages classes.
+struct CMessageClass;
+
+struct PyMessageFactory {
+  PyObject_HEAD
+
+  // 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 PyMessageFactory.
+  // The C++ one creates messages, when the Python one creates classes.
+  MessageFactory* message_factory;
+
+  // borrowed reference to a Python DescriptorPool.
+  // TODO(amauryfa): invert the dependency: the MessageFactory owns the
+  // DescriptorPool, not the opposite.
+  PyDescriptorPool* pool;
+
+  // Make our own mapping to retrieve Python classes from C++ descriptors.
+  //
+  // Descriptor pointers stored here are owned by the DescriptorPool above.
+  // Python references to classes are owned by this PyDescriptorPool.
+  typedef hash_map<const Descriptor*, CMessageClass*> ClassesByMessageMap;
+  ClassesByMessageMap* classes_by_descriptor;
+};
+
+extern PyTypeObject PyMessageFactory_Type;
+
+namespace message_factory {
+
+// Creates a new MessageFactory instance.
+PyMessageFactory* NewMessageFactory(PyTypeObject* type, PyDescriptorPool* pool);
+
+// Registers a new Python class for the given message descriptor.
+// On error, returns -1 with a Python exception set.
+int RegisterMessageClass(PyMessageFactory* self,
+                         const Descriptor* message_descriptor,
+                         CMessageClass* message_class);
+
+// Retrieves the Python class registered with the given message descriptor.
+//
+// Returns a *borrowed* reference if found, otherwise returns NULL with an
+// exception set.
+CMessageClass* GetMessageClass(PyMessageFactory* self,
+                               const Descriptor* message_descriptor);
+
+}  // namespace message_factory
+
+// Initialize objects used by this module.
+// On error, returns false with a Python exception set.
+bool InitMessageFactory();
+
+}  // namespace python
+}  // namespace protobuf
+
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_PYTHON_CPP_MESSAGE_FACTORY_H__
diff --git a/python/google/protobuf/pyext/repeated_composite_container.cc b/python/google/protobuf/pyext/repeated_composite_container.cc
index bb2f6db2..43a2bc12 100644
--- a/python/google/protobuf/pyext/repeated_composite_container.cc
+++ b/python/google/protobuf/pyext/repeated_composite_container.cc
@@ -364,7 +364,7 @@ static int SortPythonMessages(RepeatedCompositeContainer* self,
   ScopedPyObjectPtr m(PyObject_GetAttrString(self->child_messages, "sort"));
   if (m == NULL)
     return -1;
-  if (PyObject_Call(m.get(), args, kwds) == NULL)
+  if (ScopedPyObjectPtr(PyObject_Call(m.get(), args, kwds)) == NULL)
     return -1;
   if (self->message != NULL) {
     ReorderAttached(self);
diff --git a/python/google/protobuf/symbol_database.py b/python/google/protobuf/symbol_database.py
index aa466abd..ecbef211 100644
--- a/python/google/protobuf/symbol_database.py
+++ b/python/google/protobuf/symbol_database.py
@@ -129,7 +129,8 @@ class SymbolDatabase(message_factory.MessageFactory):
 
     Only messages already created and registered will be returned; (this is the
     case for imported _pb2 modules)
-    But unlike MessageFactory, this version also returns nested messages.
+    But unlike MessageFactory, this version also returns already defined nested
+    messages, but does not register any message extensions.
 
     Args:
       files: The file names to extract messages from.
diff --git a/python/google/protobuf/text_format.py b/python/google/protobuf/text_format.py
index 06b79d77..90f6ce42 100755
--- a/python/google/protobuf/text_format.py
+++ b/python/google/protobuf/text_format.py
@@ -228,13 +228,13 @@ def _BuildMessageFromTypeName(type_name, descriptor_pool):
     wasn't found matching type_name.
   """
   # pylint: disable=g-import-not-at-top
-  from google.protobuf import message_factory
-  factory = message_factory.MessageFactory(descriptor_pool)
+  from google.protobuf import symbol_database
+  database = symbol_database.Default()
   try:
     message_descriptor = descriptor_pool.FindMessageTypeByName(type_name)
   except KeyError:
     return None
-  message_type = factory.GetPrototype(message_descriptor)
+  message_type = database.GetPrototype(message_descriptor)
   return message_type()
 
 
@@ -317,8 +317,7 @@ class _Printer(object):
           # of this file to work around.
           #
           # TODO(haberman): refactor and optimize if this becomes an issue.
-          entry_submsg = field.message_type._concrete_class(key=key,
-                                                            value=value[key])
+          entry_submsg = value.GetEntryClass()(key=key, value=value[key])
           self.PrintField(field, entry_submsg)
       elif field.label == descriptor.FieldDescriptor.LABEL_REPEATED:
         for element in value:
@@ -749,8 +748,7 @@ class _Parser(object):
       if field.is_extension:
         sub_message = message.Extensions[field].add()
       elif is_map_entry:
-        # pylint: disable=protected-access
-        sub_message = field.message_type._concrete_class()
+        sub_message = getattr(message, field.name).GetEntryClass()()
       else:
         sub_message = getattr(message, field.name).add()
     else:
@@ -1448,9 +1446,9 @@ def ParseBool(text):
   Raises:
     ValueError: If text is not a valid boolean.
   """
-  if text in ('true', 't', '1'):
+  if text in ('true', 't', '1', 'True'):
     return True
-  elif text in ('false', 'f', '0'):
+  elif text in ('false', 'f', '0', 'False'):
     return False
   else:
     raise ValueError('Expected "true" or "false".')