two version of R2R are hereHEADmaster

1 files changed, 1583 insertions, 0 deletions

diff --git a/.venv/lib/python3.12/site-packages/google/protobuf/internal/python_message.py b/.venv/lib/python3.12/site-packages/google/protobuf/internal/python_message.py
new file mode 100644
index 00000000..1f901688
--- /dev/null
+++ b/.venv/lib/python3.12/site-packages/google/protobuf/internal/python_message.py
@@ -0,0 +1,1583 @@
+# Protocol Buffers - Google's data interchange format
+# Copyright 2008 Google Inc.  All rights reserved.
+#
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file or at
+# https://developers.google.com/open-source/licenses/bsd
+
+# This code is meant to work on Python 2.4 and above only.
+#
+# TODO: Helpers for verbose, common checks like seeing if a
+# descriptor's cpp_type is CPPTYPE_MESSAGE.
+
+"""Contains a metaclass and helper functions used to create
+protocol message classes from Descriptor objects at runtime.
+
+Recall that a metaclass is the "type" of a class.
+(A class is to a metaclass what an instance is to a class.)
+
+In this case, we use the GeneratedProtocolMessageType metaclass
+to inject all the useful functionality into the classes
+output by the protocol compiler at compile-time.
+
+The upshot of all this is that the real implementation
+details for ALL pure-Python protocol buffers are *here in
+this file*.
+"""
+
+__author__ = 'robinson@google.com (Will Robinson)'
+
+import datetime
+from io import BytesIO
+import struct
+import sys
+import warnings
+import weakref
+
+from google.protobuf import descriptor as descriptor_mod
+from google.protobuf import message as message_mod
+from google.protobuf import text_format
+# We use "as" to avoid name collisions with variables.
+from google.protobuf.internal import api_implementation
+from google.protobuf.internal import containers
+from google.protobuf.internal import decoder
+from google.protobuf.internal import encoder
+from google.protobuf.internal import enum_type_wrapper
+from google.protobuf.internal import extension_dict
+from google.protobuf.internal import message_listener as message_listener_mod
+from google.protobuf.internal import type_checkers
+from google.protobuf.internal import well_known_types
+from google.protobuf.internal import wire_format
+
+_FieldDescriptor = descriptor_mod.FieldDescriptor
+_AnyFullTypeName = 'google.protobuf.Any'
+_StructFullTypeName = 'google.protobuf.Struct'
+_ListValueFullTypeName = 'google.protobuf.ListValue'
+_ExtensionDict = extension_dict._ExtensionDict
+
+class GeneratedProtocolMessageType(type):
+
+  """Metaclass for protocol message classes created at runtime from Descriptors.
+
+  We add implementations for all methods described in the Message class.  We
+  also create properties to allow getting/setting all fields in the protocol
+  message.  Finally, we create slots to prevent users from accidentally
+  "setting" nonexistent fields in the protocol message, which then wouldn't get
+  serialized / deserialized properly.
+
+  The protocol compiler currently uses this metaclass to create protocol
+  message classes at runtime.  Clients can also manually create their own
+  classes at runtime, as in this example:
+
+  mydescriptor = Descriptor(.....)
+  factory = symbol_database.Default()
+  factory.pool.AddDescriptor(mydescriptor)
+  MyProtoClass = message_factory.GetMessageClass(mydescriptor)
+  myproto_instance = MyProtoClass()
+  myproto.foo_field = 23
+  ...
+  """
+
+  # Must be consistent with the protocol-compiler code in
+  # proto2/compiler/internal/generator.*.
+  _DESCRIPTOR_KEY = 'DESCRIPTOR'
+
+  def __new__(cls, name, bases, dictionary):
+    """Custom allocation for runtime-generated class types.
+
+    We override __new__ because this is apparently the only place
+    where we can meaningfully set __slots__ on the class we're creating(?).
+    (The interplay between metaclasses and slots is not very well-documented).
+
+    Args:
+      name: Name of the class (ignored, but required by the
+        metaclass protocol).
+      bases: Base classes of the class we're constructing.
+        (Should be message.Message).  We ignore this field, but
+        it's required by the metaclass protocol
+      dictionary: The class dictionary of the class we're
+        constructing.  dictionary[_DESCRIPTOR_KEY] must contain
+        a Descriptor object describing this protocol message
+        type.
+
+    Returns:
+      Newly-allocated class.
+
+    Raises:
+      RuntimeError: Generated code only work with python cpp extension.
+    """
+    descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
+
+    if isinstance(descriptor, str):
+      raise RuntimeError('The generated code only work with python cpp '
+                         'extension, but it is using pure python runtime.')
+
+    # If a concrete class already exists for this descriptor, don't try to
+    # create another.  Doing so will break any messages that already exist with
+    # the existing class.
+    #
+    # The C++ implementation appears to have its own internal `PyMessageFactory`
+    # to achieve similar results.
+    #
+    # This most commonly happens in `text_format.py` when using descriptors from
+    # a custom pool; it calls message_factory.GetMessageClass() on a
+    # descriptor which already has an existing concrete class.
+    new_class = getattr(descriptor, '_concrete_class', None)
+    if new_class:
+      return new_class
+
+    if descriptor.full_name in well_known_types.WKTBASES:
+      bases += (well_known_types.WKTBASES[descriptor.full_name],)
+    _AddClassAttributesForNestedExtensions(descriptor, dictionary)
+    _AddSlots(descriptor, dictionary)
+
+    superclass = super(GeneratedProtocolMessageType, cls)
+    new_class = superclass.__new__(cls, name, bases, dictionary)
+    return new_class
+
+  def __init__(cls, name, bases, dictionary):
+    """Here we perform the majority of our work on the class.
+    We add enum getters, an __init__ method, implementations
+    of all Message methods, and properties for all fields
+    in the protocol type.
+
+    Args:
+      name: Name of the class (ignored, but required by the
+        metaclass protocol).
+      bases: Base classes of the class we're constructing.
+        (Should be message.Message).  We ignore this field, but
+        it's required by the metaclass protocol
+      dictionary: The class dictionary of the class we're
+        constructing.  dictionary[_DESCRIPTOR_KEY] must contain
+        a Descriptor object describing this protocol message
+        type.
+    """
+    descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
+
+    # If this is an _existing_ class looked up via `_concrete_class` in the
+    # __new__ method above, then we don't need to re-initialize anything.
+    existing_class = getattr(descriptor, '_concrete_class', None)
+    if existing_class:
+      assert existing_class is cls, (
+          'Duplicate `GeneratedProtocolMessageType` created for descriptor %r'
+          % (descriptor.full_name))
+      return
+
+    cls._message_set_decoders_by_tag = {}
+    cls._fields_by_tag = {}
+    if (descriptor.has_options and
+        descriptor.GetOptions().message_set_wire_format):
+      cls._message_set_decoders_by_tag[decoder.MESSAGE_SET_ITEM_TAG] = (
+          decoder.MessageSetItemDecoder(descriptor),
+          None,
+      )
+
+    # Attach stuff to each FieldDescriptor for quick lookup later on.
+    for field in descriptor.fields:
+      _AttachFieldHelpers(cls, field)
+
+    if descriptor.is_extendable and hasattr(descriptor.file, 'pool'):
+      extensions = descriptor.file.pool.FindAllExtensions(descriptor)
+      for ext in extensions:
+        _AttachFieldHelpers(cls, ext)
+
+    descriptor._concrete_class = cls  # pylint: disable=protected-access
+    _AddEnumValues(descriptor, cls)
+    _AddInitMethod(descriptor, cls)
+    _AddPropertiesForFields(descriptor, cls)
+    _AddPropertiesForExtensions(descriptor, cls)
+    _AddStaticMethods(cls)
+    _AddMessageMethods(descriptor, cls)
+    _AddPrivateHelperMethods(descriptor, cls)
+
+    superclass = super(GeneratedProtocolMessageType, cls)
+    superclass.__init__(name, bases, dictionary)
+
+
+# Stateless helpers for GeneratedProtocolMessageType below.
+# Outside clients should not access these directly.
+#
+# I opted not to make any of these methods on the metaclass, to make it more
+# clear that I'm not really using any state there and to keep clients from
+# thinking that they have direct access to these construction helpers.
+
+
+def _PropertyName(proto_field_name):
+  """Returns the name of the public property attribute which
+  clients can use to get and (in some cases) set the value
+  of a protocol message field.
+
+  Args:
+    proto_field_name: The protocol message field name, exactly
+      as it appears (or would appear) in a .proto file.
+  """
+  # TODO: Escape Python keywords (e.g., yield), and test this support.
+  # nnorwitz makes my day by writing:
+  # """
+  # FYI.  See the keyword module in the stdlib. This could be as simple as:
+  #
+  # if keyword.iskeyword(proto_field_name):
+  #   return proto_field_name + "_"
+  # return proto_field_name
+  # """
+  # Kenton says:  The above is a BAD IDEA.  People rely on being able to use
+  #   getattr() and setattr() to reflectively manipulate field values.  If we
+  #   rename the properties, then every such user has to also make sure to apply
+  #   the same transformation.  Note that currently if you name a field "yield",
+  #   you can still access it just fine using getattr/setattr -- it's not even
+  #   that cumbersome to do so.
+  # TODO:  Remove this method entirely if/when everyone agrees with my
+  #   position.
+  return proto_field_name
+
+
+def _AddSlots(message_descriptor, dictionary):
+  """Adds a __slots__ entry to dictionary, containing the names of all valid
+  attributes for this message type.
+
+  Args:
+    message_descriptor: A Descriptor instance describing this message type.
+    dictionary: Class dictionary to which we'll add a '__slots__' entry.
+  """
+  dictionary['__slots__'] = ['_cached_byte_size',
+                             '_cached_byte_size_dirty',
+                             '_fields',
+                             '_unknown_fields',
+                             '_is_present_in_parent',
+                             '_listener',
+                             '_listener_for_children',
+                             '__weakref__',
+                             '_oneofs']
+
+
+def _IsMessageSetExtension(field):
+  return (field.is_extension and
+          field.containing_type.has_options and
+          field.containing_type.GetOptions().message_set_wire_format and
+          field.type == _FieldDescriptor.TYPE_MESSAGE and
+          field.label == _FieldDescriptor.LABEL_OPTIONAL)
+
+
+def _IsMapField(field):
+  return (field.type == _FieldDescriptor.TYPE_MESSAGE and
+          field.message_type._is_map_entry)
+
+
+def _IsMessageMapField(field):
+  value_type = field.message_type.fields_by_name['value']
+  return value_type.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE
+
+def _AttachFieldHelpers(cls, field_descriptor):
+  is_repeated = field_descriptor.label == _FieldDescriptor.LABEL_REPEATED
+  field_descriptor._default_constructor = _DefaultValueConstructorForField(
+      field_descriptor
+  )
+
+  def AddFieldByTag(wiretype, is_packed):
+    tag_bytes = encoder.TagBytes(field_descriptor.number, wiretype)
+    cls._fields_by_tag[tag_bytes] = (field_descriptor, is_packed)
+
+  AddFieldByTag(
+      type_checkers.FIELD_TYPE_TO_WIRE_TYPE[field_descriptor.type], False
+  )
+
+  if is_repeated and wire_format.IsTypePackable(field_descriptor.type):
+    # To support wire compatibility of adding packed = true, add a decoder for
+    # packed values regardless of the field's options.
+    AddFieldByTag(wire_format.WIRETYPE_LENGTH_DELIMITED, True)
+
+
+def _MaybeAddEncoder(cls, field_descriptor):
+  if hasattr(field_descriptor, '_encoder'):
+    return
+  is_repeated = (field_descriptor.label == _FieldDescriptor.LABEL_REPEATED)
+  is_map_entry = _IsMapField(field_descriptor)
+  is_packed = field_descriptor.is_packed
+
+  if is_map_entry:
+    field_encoder = encoder.MapEncoder(field_descriptor)
+    sizer = encoder.MapSizer(field_descriptor,
+                             _IsMessageMapField(field_descriptor))
+  elif _IsMessageSetExtension(field_descriptor):
+    field_encoder = encoder.MessageSetItemEncoder(field_descriptor.number)
+    sizer = encoder.MessageSetItemSizer(field_descriptor.number)
+  else:
+    field_encoder = type_checkers.TYPE_TO_ENCODER[field_descriptor.type](
+        field_descriptor.number, is_repeated, is_packed)
+    sizer = type_checkers.TYPE_TO_SIZER[field_descriptor.type](
+        field_descriptor.number, is_repeated, is_packed)
+
+  field_descriptor._sizer = sizer
+  field_descriptor._encoder = field_encoder
+
+
+def _MaybeAddDecoder(cls, field_descriptor):
+  if hasattr(field_descriptor, '_decoders'):
+    return
+
+  is_repeated = field_descriptor.label == _FieldDescriptor.LABEL_REPEATED
+  is_map_entry = _IsMapField(field_descriptor)
+  helper_decoders = {}
+
+  def AddDecoder(is_packed):
+    decode_type = field_descriptor.type
+    if (decode_type == _FieldDescriptor.TYPE_ENUM and
+        not field_descriptor.enum_type.is_closed):
+      decode_type = _FieldDescriptor.TYPE_INT32
+
+    oneof_descriptor = None
+    if field_descriptor.containing_oneof is not None:
+      oneof_descriptor = field_descriptor
+
+    if is_map_entry:
+      is_message_map = _IsMessageMapField(field_descriptor)
+
+      field_decoder = decoder.MapDecoder(
+          field_descriptor, _GetInitializeDefaultForMap(field_descriptor),
+          is_message_map)
+    elif decode_type == _FieldDescriptor.TYPE_STRING:
+      field_decoder = decoder.StringDecoder(
+          field_descriptor.number, is_repeated, is_packed,
+          field_descriptor, field_descriptor._default_constructor,
+          not field_descriptor.has_presence)
+    elif field_descriptor.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+      field_decoder = type_checkers.TYPE_TO_DECODER[decode_type](
+          field_descriptor.number, is_repeated, is_packed,
+          field_descriptor, field_descriptor._default_constructor)
+    else:
+      field_decoder = type_checkers.TYPE_TO_DECODER[decode_type](
+          field_descriptor.number, is_repeated, is_packed,
+          # pylint: disable=protected-access
+          field_descriptor, field_descriptor._default_constructor,
+          not field_descriptor.has_presence)
+
+    helper_decoders[is_packed] = field_decoder
+
+  AddDecoder(False)
+
+  if is_repeated and wire_format.IsTypePackable(field_descriptor.type):
+    # To support wire compatibility of adding packed = true, add a decoder for
+    # packed values regardless of the field's options.
+    AddDecoder(True)
+
+  field_descriptor._decoders = helper_decoders
+
+
+def _AddClassAttributesForNestedExtensions(descriptor, dictionary):
+  extensions = descriptor.extensions_by_name
+  for extension_name, extension_field in extensions.items():
+    assert extension_name not in dictionary
+    dictionary[extension_name] = extension_field
+
+
+def _AddEnumValues(descriptor, cls):
+  """Sets class-level attributes for all enum fields defined in this message.
+
+  Also exporting a class-level object that can name enum values.
+
+  Args:
+    descriptor: Descriptor object for this message type.
+    cls: Class we're constructing for this message type.
+  """
+  for enum_type in descriptor.enum_types:
+    setattr(cls, enum_type.name, enum_type_wrapper.EnumTypeWrapper(enum_type))
+    for enum_value in enum_type.values:
+      setattr(cls, enum_value.name, enum_value.number)
+
+
+def _GetInitializeDefaultForMap(field):
+  if field.label != _FieldDescriptor.LABEL_REPEATED:
+    raise ValueError('map_entry set on non-repeated field %s' % (
+        field.name))
+  fields_by_name = field.message_type.fields_by_name
+  key_checker = type_checkers.GetTypeChecker(fields_by_name['key'])
+
+  value_field = fields_by_name['value']
+  if _IsMessageMapField(field):
+    def MakeMessageMapDefault(message):
+      return containers.MessageMap(
+          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,
+          field.message_type)
+    return MakePrimitiveMapDefault
+
+def _DefaultValueConstructorForField(field):
+  """Returns a function which returns a default value for a field.
+
+  Args:
+    field: FieldDescriptor object for this field.
+
+  The returned function has one argument:
+    message: Message instance containing this field, or a weakref proxy
+      of same.
+
+  That function in turn returns a default value for this field.  The default
+    value may refer back to |message| via a weak reference.
+  """
+
+  if _IsMapField(field):
+    return _GetInitializeDefaultForMap(field)
+
+  if field.label == _FieldDescriptor.LABEL_REPEATED:
+    if field.has_default_value and field.default_value != []:
+      raise ValueError('Repeated field default value not empty list: %s' % (
+          field.default_value))
+    if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+      # We can't look at _concrete_class yet since it might not have
+      # been set.  (Depends on order in which we initialize the classes).
+      message_type = field.message_type
+      def MakeRepeatedMessageDefault(message):
+        return containers.RepeatedCompositeFieldContainer(
+            message._listener_for_children, field.message_type)
+      return MakeRepeatedMessageDefault
+    else:
+      type_checker = type_checkers.GetTypeChecker(field)
+      def MakeRepeatedScalarDefault(message):
+        return containers.RepeatedScalarFieldContainer(
+            message._listener_for_children, type_checker)
+      return MakeRepeatedScalarDefault
+
+  if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+    message_type = field.message_type
+    def MakeSubMessageDefault(message):
+      # _concrete_class may not yet be initialized.
+      if not hasattr(message_type, '_concrete_class'):
+        from google.protobuf import message_factory
+        message_factory.GetMessageClass(message_type)
+      result = message_type._concrete_class()
+      result._SetListener(
+          _OneofListener(message, field)
+          if field.containing_oneof is not None
+          else message._listener_for_children)
+      return result
+    return MakeSubMessageDefault
+
+  def MakeScalarDefault(message):
+    # TODO: This may be broken since there may not be
+    # default_value.  Combine with has_default_value somehow.
+    return field.default_value
+  return MakeScalarDefault
+
+
+def _ReraiseTypeErrorWithFieldName(message_name, field_name):
+  """Re-raise the currently-handled TypeError with the field name added."""
+  exc = sys.exc_info()[1]
+  if len(exc.args) == 1 and type(exc) is TypeError:
+    # simple TypeError; add field name to exception message
+    exc = TypeError('%s for field %s.%s' % (str(exc), message_name, field_name))
+
+  # re-raise possibly-amended exception with original traceback:
+  raise exc.with_traceback(sys.exc_info()[2])
+
+
+def _AddInitMethod(message_descriptor, cls):
+  """Adds an __init__ method to cls."""
+
+  def _GetIntegerEnumValue(enum_type, value):
+    """Convert a string or integer enum value to an integer.
+
+    If the value is a string, it is converted to the enum value in
+    enum_type with the same name.  If the value is not a string, it's
+    returned as-is.  (No conversion or bounds-checking is done.)
+    """
+    if isinstance(value, str):
+      try:
+        return enum_type.values_by_name[value].number
+      except KeyError:
+        raise ValueError('Enum type %s: unknown label "%s"' % (
+            enum_type.full_name, value))
+    return value
+
+  def init(self, **kwargs):
+    self._cached_byte_size = 0
+    self._cached_byte_size_dirty = len(kwargs) > 0
+    self._fields = {}
+    # Contains a mapping from oneof field descriptors to the descriptor
+    # of the currently set field in that oneof field.
+    self._oneofs = {}
+
+    # _unknown_fields is () when empty for efficiency, and will be turned into
+    # a list if fields are added.
+    self._unknown_fields = ()
+    self._is_present_in_parent = False
+    self._listener = message_listener_mod.NullMessageListener()
+    self._listener_for_children = _Listener(self)
+    for field_name, field_value in kwargs.items():
+      field = _GetFieldByName(message_descriptor, field_name)
+      if field is None:
+        raise TypeError('%s() got an unexpected keyword argument "%s"' %
+                        (message_descriptor.name, field_name))
+      if field_value is None:
+        # field=None is the same as no field at all.
+        continue
+      if field.label == _FieldDescriptor.LABEL_REPEATED:
+        field_copy = field._default_constructor(self)
+        if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:  # Composite
+          if _IsMapField(field):
+            if _IsMessageMapField(field):
+              for key in field_value:
+                field_copy[key].MergeFrom(field_value[key])
+            else:
+              field_copy.update(field_value)
+          else:
+            for val in field_value:
+              if isinstance(val, dict):
+                field_copy.add(**val)
+              else:
+                field_copy.add().MergeFrom(val)
+        else:  # Scalar
+          if field.cpp_type == _FieldDescriptor.CPPTYPE_ENUM:
+            field_value = [_GetIntegerEnumValue(field.enum_type, val)
+                           for val in field_value]
+          field_copy.extend(field_value)
+        self._fields[field] = field_copy
+      elif field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+        field_copy = field._default_constructor(self)
+        new_val = None
+        if isinstance(field_value, message_mod.Message):
+          new_val = field_value
+        elif isinstance(field_value, dict):
+          if field.message_type.full_name == _StructFullTypeName:
+            field_copy.Clear()
+            if len(field_value) == 1 and 'fields' in field_value:
+              try:
+                field_copy.update(field_value)
+              except:
+                # Fall back to init normal message field
+                field_copy.Clear()
+                new_val = field.message_type._concrete_class(**field_value)
+            else:
+              field_copy.update(field_value)
+          else:
+            new_val = field.message_type._concrete_class(**field_value)
+        elif hasattr(field_copy, '_internal_assign'):
+          field_copy._internal_assign(field_value)
+        else:
+          raise TypeError(
+              'Message field {0}.{1} must be initialized with a '
+              'dict or instance of same class, got {2}.'.format(
+                  message_descriptor.name,
+                  field_name,
+                  type(field_value).__name__,
+              )
+          )
+
+        if new_val != None:
+          try:
+            field_copy.MergeFrom(new_val)
+          except TypeError:
+            _ReraiseTypeErrorWithFieldName(message_descriptor.name, field_name)
+        self._fields[field] = field_copy
+      else:
+        if field.cpp_type == _FieldDescriptor.CPPTYPE_ENUM:
+          field_value = _GetIntegerEnumValue(field.enum_type, field_value)
+        try:
+          setattr(self, field_name, field_value)
+        except TypeError:
+          _ReraiseTypeErrorWithFieldName(message_descriptor.name, field_name)
+
+  init.__module__ = None
+  init.__doc__ = None
+  cls.__init__ = init
+
+
+def _GetFieldByName(message_descriptor, field_name):
+  """Returns a field descriptor by field name.
+
+  Args:
+    message_descriptor: A Descriptor describing all fields in message.
+    field_name: The name of the field to retrieve.
+  Returns:
+    The field descriptor associated with the field name.
+  """
+  try:
+    return message_descriptor.fields_by_name[field_name]
+  except KeyError:
+    raise ValueError('Protocol message %s has no "%s" field.' %
+                     (message_descriptor.name, field_name))
+
+
+def _AddPropertiesForFields(descriptor, cls):
+  """Adds properties for all fields in this protocol message type."""
+  for field in descriptor.fields:
+    _AddPropertiesForField(field, cls)
+
+  if descriptor.is_extendable:
+    # _ExtensionDict is just an adaptor with no state so we allocate a new one
+    # every time it is accessed.
+    cls.Extensions = property(lambda self: _ExtensionDict(self))
+
+
+def _AddPropertiesForField(field, cls):
+  """Adds a public property for a protocol message field.
+  Clients can use this property to get and (in the case
+  of non-repeated scalar fields) directly set the value
+  of a protocol message field.
+
+  Args:
+    field: A FieldDescriptor for this field.
+    cls: The class we're constructing.
+  """
+  # Catch it if we add other types that we should
+  # handle specially here.
+  assert _FieldDescriptor.MAX_CPPTYPE == 10
+
+  constant_name = field.name.upper() + '_FIELD_NUMBER'
+  setattr(cls, constant_name, field.number)
+
+  if field.label == _FieldDescriptor.LABEL_REPEATED:
+    _AddPropertiesForRepeatedField(field, cls)
+  elif field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+    _AddPropertiesForNonRepeatedCompositeField(field, cls)
+  else:
+    _AddPropertiesForNonRepeatedScalarField(field, cls)
+
+
+class _FieldProperty(property):
+  __slots__ = ('DESCRIPTOR',)
+
+  def __init__(self, descriptor, getter, setter, doc):
+    property.__init__(self, getter, setter, doc=doc)
+    self.DESCRIPTOR = descriptor
+
+
+def _AddPropertiesForRepeatedField(field, cls):
+  """Adds a public property for a "repeated" protocol message field.  Clients
+  can use this property to get the value of the field, which will be either a
+  RepeatedScalarFieldContainer or RepeatedCompositeFieldContainer (see
+  below).
+
+  Note that when clients add values to these containers, we perform
+  type-checking in the case of repeated scalar fields, and we also set any
+  necessary "has" bits as a side-effect.
+
+  Args:
+    field: A FieldDescriptor for this field.
+    cls: The class we're constructing.
+  """
+  proto_field_name = field.name
+  property_name = _PropertyName(proto_field_name)
+
+  def getter(self):
+    field_value = self._fields.get(field)
+    if field_value is None:
+      # Construct a new object to represent this field.
+      field_value = field._default_constructor(self)
+
+      # Atomically check if another thread has preempted us and, if not, swap
+      # in the new object we just created.  If someone has preempted us, we
+      # take that object and discard ours.
+      # WARNING:  We are relying on setdefault() being atomic.  This is true
+      #   in CPython but we haven't investigated others.  This warning appears
+      #   in several other locations in this file.
+      field_value = self._fields.setdefault(field, field_value)
+    return field_value
+  getter.__module__ = None
+  getter.__doc__ = 'Getter for %s.' % proto_field_name
+
+  # We define a setter just so we can throw an exception with a more
+  # helpful error message.
+  def setter(self, new_value):
+    raise AttributeError('Assignment not allowed to repeated field '
+                         '"%s" in protocol message object.' % proto_field_name)
+
+  doc = 'Magic attribute generated for "%s" proto field.' % proto_field_name
+  setattr(cls, property_name, _FieldProperty(field, getter, setter, doc=doc))
+
+
+def _AddPropertiesForNonRepeatedScalarField(field, cls):
+  """Adds a public property for a nonrepeated, scalar protocol message field.
+  Clients can use this property to get and directly set the value of the field.
+  Note that when the client sets the value of a field by using this property,
+  all necessary "has" bits are set as a side-effect, and we also perform
+  type-checking.
+
+  Args:
+    field: A FieldDescriptor for this field.
+    cls: The class we're constructing.
+  """
+  proto_field_name = field.name
+  property_name = _PropertyName(proto_field_name)
+  type_checker = type_checkers.GetTypeChecker(field)
+  default_value = field.default_value
+
+  def getter(self):
+    # TODO: This may be broken since there may not be
+    # default_value.  Combine with has_default_value somehow.
+    return self._fields.get(field, default_value)
+  getter.__module__ = None
+  getter.__doc__ = 'Getter for %s.' % proto_field_name
+
+  def field_setter(self, new_value):
+    # pylint: disable=protected-access
+    # Testing the value for truthiness captures all of the proto3 defaults
+    # (0, 0.0, enum 0, and False).
+    try:
+      new_value = type_checker.CheckValue(new_value)
+    except TypeError as e:
+      raise TypeError(
+          'Cannot set %s to %.1024r: %s' % (field.full_name, new_value, e))
+    if not field.has_presence and not new_value:
+      self._fields.pop(field, None)
+    else:
+      self._fields[field] = new_value
+    # Check _cached_byte_size_dirty inline to improve performance, since scalar
+    # setters are called frequently.
+    if not self._cached_byte_size_dirty:
+      self._Modified()
+
+  if field.containing_oneof:
+    def setter(self, new_value):
+      field_setter(self, new_value)
+      self._UpdateOneofState(field)
+  else:
+    setter = field_setter
+
+  setter.__module__ = None
+  setter.__doc__ = 'Setter for %s.' % proto_field_name
+
+  # Add a property to encapsulate the getter/setter.
+  doc = 'Magic attribute generated for "%s" proto field.' % proto_field_name
+  setattr(cls, property_name, _FieldProperty(field, getter, setter, doc=doc))
+
+
+def _AddPropertiesForNonRepeatedCompositeField(field, cls):
+  """Adds a public property for a nonrepeated, composite protocol message field.
+  A composite field is a "group" or "message" field.
+
+  Clients can use this property to get the value of the field, but cannot
+  assign to the property directly.
+
+  Args:
+    field: A FieldDescriptor for this field.
+    cls: The class we're constructing.
+  """
+  # TODO: Remove duplication with similar method
+  # for non-repeated scalars.
+  proto_field_name = field.name
+  property_name = _PropertyName(proto_field_name)
+
+  def getter(self):
+    field_value = self._fields.get(field)
+    if field_value is None:
+      # Construct a new object to represent this field.
+      field_value = field._default_constructor(self)
+
+      # Atomically check if another thread has preempted us and, if not, swap
+      # in the new object we just created.  If someone has preempted us, we
+      # take that object and discard ours.
+      # WARNING:  We are relying on setdefault() being atomic.  This is true
+      #   in CPython but we haven't investigated others.  This warning appears
+      #   in several other locations in this file.
+      field_value = self._fields.setdefault(field, field_value)
+    return field_value
+  getter.__module__ = None
+  getter.__doc__ = 'Getter for %s.' % proto_field_name
+
+  # We define a setter just so we can throw an exception with a more
+  # helpful error message.
+  def setter(self, new_value):
+    if field.message_type.full_name == 'google.protobuf.Timestamp':
+      getter(self)
+      self._fields[field].FromDatetime(new_value)
+    elif field.message_type.full_name == 'google.protobuf.Duration':
+      getter(self)
+      self._fields[field].FromTimedelta(new_value)
+    elif field.message_type.full_name == _StructFullTypeName:
+      getter(self)
+      self._fields[field].Clear()
+      self._fields[field].update(new_value)
+    elif field.message_type.full_name == _ListValueFullTypeName:
+      getter(self)
+      self._fields[field].Clear()
+      self._fields[field].extend(new_value)
+    else:
+      raise AttributeError(
+          'Assignment not allowed to composite field '
+          '"%s" in protocol message object.' % proto_field_name
+      )
+
+  # Add a property to encapsulate the getter.
+  doc = 'Magic attribute generated for "%s" proto field.' % proto_field_name
+  setattr(cls, property_name, _FieldProperty(field, getter, setter, doc=doc))
+
+
+def _AddPropertiesForExtensions(descriptor, cls):
+  """Adds properties for all fields in this protocol message type."""
+  extensions = descriptor.extensions_by_name
+  for extension_name, extension_field in extensions.items():
+    constant_name = extension_name.upper() + '_FIELD_NUMBER'
+    setattr(cls, constant_name, extension_field.number)
+
+  # TODO: Migrate all users of these attributes to functions like
+  #   pool.FindExtensionByNumber(descriptor).
+  if descriptor.file is not None:
+    # TODO: Use cls.MESSAGE_FACTORY.pool when available.
+    pool = descriptor.file.pool
+
+def _AddStaticMethods(cls):
+  def FromString(s):
+    message = cls()
+    message.MergeFromString(s)
+    return message
+  cls.FromString = staticmethod(FromString)
+
+
+def _IsPresent(item):
+  """Given a (FieldDescriptor, value) tuple from _fields, return true if the
+  value should be included in the list returned by ListFields()."""
+
+  if item[0].label == _FieldDescriptor.LABEL_REPEATED:
+    return bool(item[1])
+  elif item[0].cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+    return item[1]._is_present_in_parent
+  else:
+    return True
+
+
+def _AddListFieldsMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+
+  def ListFields(self):
+    all_fields = [item for item in self._fields.items() if _IsPresent(item)]
+    all_fields.sort(key = lambda item: item[0].number)
+    return all_fields
+
+  cls.ListFields = ListFields
+
+
+def _AddHasFieldMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+
+  hassable_fields = {}
+  for field in message_descriptor.fields:
+    if field.label == _FieldDescriptor.LABEL_REPEATED:
+      continue
+    # For proto3, only submessages and fields inside a oneof have presence.
+    if not field.has_presence:
+      continue
+    hassable_fields[field.name] = field
+
+  # Has methods are supported for oneof descriptors.
+  for oneof in message_descriptor.oneofs:
+    hassable_fields[oneof.name] = oneof
+
+  def HasField(self, field_name):
+    try:
+      field = hassable_fields[field_name]
+    except KeyError as exc:
+      raise ValueError('Protocol message %s has no non-repeated field "%s" '
+                       'nor has presence is not available for this field.' % (
+                           message_descriptor.full_name, field_name)) from exc
+
+    if isinstance(field, descriptor_mod.OneofDescriptor):
+      try:
+        return HasField(self, self._oneofs[field].name)
+      except KeyError:
+        return False
+    else:
+      if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+        value = self._fields.get(field)
+        return value is not None and value._is_present_in_parent
+      else:
+        return field in self._fields
+
+  cls.HasField = HasField
+
+
+def _AddClearFieldMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+  def ClearField(self, field_name):
+    try:
+      field = message_descriptor.fields_by_name[field_name]
+    except KeyError:
+      try:
+        field = message_descriptor.oneofs_by_name[field_name]
+        if field in self._oneofs:
+          field = self._oneofs[field]
+        else:
+          return
+      except KeyError:
+        raise ValueError('Protocol message %s has no "%s" field.' %
+                         (message_descriptor.name, field_name))
+
+    if field in self._fields:
+      # To match the C++ implementation, we need to invalidate iterators
+      # for map fields when ClearField() happens.
+      if hasattr(self._fields[field], 'InvalidateIterators'):
+        self._fields[field].InvalidateIterators()
+
+      # Note:  If the field is a sub-message, its listener will still point
+      #   at us.  That's fine, because the worst than can happen is that it
+      #   will call _Modified() and invalidate our byte size.  Big deal.
+      del self._fields[field]
+
+      if self._oneofs.get(field.containing_oneof, None) is field:
+        del self._oneofs[field.containing_oneof]
+
+    # Always call _Modified() -- even if nothing was changed, this is
+    # a mutating method, and thus calling it should cause the field to become
+    # present in the parent message.
+    self._Modified()
+
+  cls.ClearField = ClearField
+
+
+def _AddClearExtensionMethod(cls):
+  """Helper for _AddMessageMethods()."""
+  def ClearExtension(self, field_descriptor):
+    extension_dict._VerifyExtensionHandle(self, field_descriptor)
+
+    # Similar to ClearField(), above.
+    if field_descriptor in self._fields:
+      del self._fields[field_descriptor]
+    self._Modified()
+  cls.ClearExtension = ClearExtension
+
+
+def _AddHasExtensionMethod(cls):
+  """Helper for _AddMessageMethods()."""
+  def HasExtension(self, field_descriptor):
+    extension_dict._VerifyExtensionHandle(self, field_descriptor)
+    if field_descriptor.label == _FieldDescriptor.LABEL_REPEATED:
+      raise KeyError('"%s" is repeated.' % field_descriptor.full_name)
+
+    if field_descriptor.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+      value = self._fields.get(field_descriptor)
+      return value is not None and value._is_present_in_parent
+    else:
+      return field_descriptor in self._fields
+  cls.HasExtension = HasExtension
+
+def _InternalUnpackAny(msg):
+  """Unpacks Any message and returns the unpacked message.
+
+  This internal method is different from public Any Unpack method which takes
+  the target message as argument. _InternalUnpackAny method does not have
+  target message type and need to find the message type in descriptor pool.
+
+  Args:
+    msg: An Any message to be unpacked.
+
+  Returns:
+    The unpacked message.
+  """
+  # TODO: Don't use the factory of generated messages.
+  # To make Any work with custom factories, use the message factory of the
+  # parent message.
+  # pylint: disable=g-import-not-at-top
+  from google.protobuf import symbol_database
+  factory = symbol_database.Default()
+
+  type_url = msg.type_url
+
+  if not type_url:
+    return None
+
+  # TODO: For now we just strip the hostname.  Better logic will be
+  # required.
+  type_name = type_url.split('/')[-1]
+  descriptor = factory.pool.FindMessageTypeByName(type_name)
+
+  if descriptor is None:
+    return None
+
+  # Unable to import message_factory at top because of circular import.
+  # pylint: disable=g-import-not-at-top
+  from google.protobuf import message_factory
+  message_class = message_factory.GetMessageClass(descriptor)
+  message = message_class()
+
+  message.ParseFromString(msg.value)
+  return message
+
+
+def _AddEqualsMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+  def __eq__(self, other):
+    if self.DESCRIPTOR.full_name == _ListValueFullTypeName and isinstance(
+        other, list
+    ):
+      return self._internal_compare(other)
+    if self.DESCRIPTOR.full_name == _StructFullTypeName and isinstance(
+        other, dict
+    ):
+      return self._internal_compare(other)
+
+    if (not isinstance(other, message_mod.Message) or
+        other.DESCRIPTOR != self.DESCRIPTOR):
+      return NotImplemented
+
+    if self is other:
+      return True
+
+    if self.DESCRIPTOR.full_name == _AnyFullTypeName:
+      any_a = _InternalUnpackAny(self)
+      any_b = _InternalUnpackAny(other)
+      if any_a and any_b:
+        return any_a == any_b
+
+    if not self.ListFields() == other.ListFields():
+      return False
+
+    # TODO: Fix UnknownFieldSet to consider MessageSet extensions,
+    # then use it for the comparison.
+    unknown_fields = list(self._unknown_fields)
+    unknown_fields.sort()
+    other_unknown_fields = list(other._unknown_fields)
+    other_unknown_fields.sort()
+    return unknown_fields == other_unknown_fields
+
+  cls.__eq__ = __eq__
+
+
+def _AddStrMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+  def __str__(self):
+    return text_format.MessageToString(self)
+  cls.__str__ = __str__
+
+
+def _AddReprMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+  def __repr__(self):
+    return text_format.MessageToString(self)
+  cls.__repr__ = __repr__
+
+
+def _AddUnicodeMethod(unused_message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+
+  def __unicode__(self):
+    return text_format.MessageToString(self, as_utf8=True).decode('utf-8')
+  cls.__unicode__ = __unicode__
+
+
+def _AddContainsMethod(message_descriptor, cls):
+
+  if message_descriptor.full_name == 'google.protobuf.Struct':
+    def __contains__(self, key):
+      return key in self.fields
+  elif message_descriptor.full_name == 'google.protobuf.ListValue':
+    def __contains__(self, value):
+      return value in self.items()
+  else:
+    def __contains__(self, field):
+      return self.HasField(field)
+
+  cls.__contains__ = __contains__
+
+
+def _BytesForNonRepeatedElement(value, field_number, field_type):
+  """Returns the number of bytes needed to serialize a non-repeated element.
+  The returned byte count includes space for tag information and any
+  other additional space associated with serializing value.
+
+  Args:
+    value: Value we're serializing.
+    field_number: Field number of this value.  (Since the field number
+      is stored as part of a varint-encoded tag, this has an impact
+      on the total bytes required to serialize the value).
+    field_type: The type of the field.  One of the TYPE_* constants
+      within FieldDescriptor.
+  """
+  try:
+    fn = type_checkers.TYPE_TO_BYTE_SIZE_FN[field_type]
+    return fn(field_number, value)
+  except KeyError:
+    raise message_mod.EncodeError('Unrecognized field type: %d' % field_type)
+
+
+def _AddByteSizeMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+
+  def ByteSize(self):
+    if not self._cached_byte_size_dirty:
+      return self._cached_byte_size
+
+    size = 0
+    descriptor = self.DESCRIPTOR
+    if descriptor._is_map_entry:
+      # Fields of map entry should always be serialized.
+      key_field = descriptor.fields_by_name['key']
+      _MaybeAddEncoder(cls, key_field)
+      size = key_field._sizer(self.key)
+      value_field = descriptor.fields_by_name['value']
+      _MaybeAddEncoder(cls, value_field)
+      size += value_field._sizer(self.value)
+    else:
+      for field_descriptor, field_value in self.ListFields():
+        _MaybeAddEncoder(cls, field_descriptor)
+        size += field_descriptor._sizer(field_value)
+      for tag_bytes, value_bytes in self._unknown_fields:
+        size += len(tag_bytes) + len(value_bytes)
+
+    self._cached_byte_size = size
+    self._cached_byte_size_dirty = False
+    self._listener_for_children.dirty = False
+    return size
+
+  cls.ByteSize = ByteSize
+
+
+def _AddSerializeToStringMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+
+  def SerializeToString(self, **kwargs):
+    # Check if the message has all of its required fields set.
+    if not self.IsInitialized():
+      raise message_mod.EncodeError(
+          'Message %s is missing required fields: %s' % (
+          self.DESCRIPTOR.full_name, ','.join(self.FindInitializationErrors())))
+    return self.SerializePartialToString(**kwargs)
+  cls.SerializeToString = SerializeToString
+
+
+def _AddSerializePartialToStringMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+
+  def SerializePartialToString(self, **kwargs):
+    out = BytesIO()
+    self._InternalSerialize(out.write, **kwargs)
+    return out.getvalue()
+  cls.SerializePartialToString = SerializePartialToString
+
+  def InternalSerialize(self, write_bytes, deterministic=None):
+    if deterministic is None:
+      deterministic = (
+          api_implementation.IsPythonDefaultSerializationDeterministic())
+    else:
+      deterministic = bool(deterministic)
+
+    descriptor = self.DESCRIPTOR
+    if descriptor._is_map_entry:
+      # Fields of map entry should always be serialized.
+      key_field = descriptor.fields_by_name['key']
+      _MaybeAddEncoder(cls, key_field)
+      key_field._encoder(write_bytes, self.key, deterministic)
+      value_field = descriptor.fields_by_name['value']
+      _MaybeAddEncoder(cls, value_field)
+      value_field._encoder(write_bytes, self.value, deterministic)
+    else:
+      for field_descriptor, field_value in self.ListFields():
+        _MaybeAddEncoder(cls, field_descriptor)
+        field_descriptor._encoder(write_bytes, field_value, deterministic)
+      for tag_bytes, value_bytes in self._unknown_fields:
+        write_bytes(tag_bytes)
+        write_bytes(value_bytes)
+  cls._InternalSerialize = InternalSerialize
+
+
+def _AddMergeFromStringMethod(message_descriptor, cls):
+  """Helper for _AddMessageMethods()."""
+  def MergeFromString(self, serialized):
+    serialized = memoryview(serialized)
+    length = len(serialized)
+    try:
+      if self._InternalParse(serialized, 0, length) != length:
+        # The only reason _InternalParse would return early is if it
+        # encountered an end-group tag.
+        raise message_mod.DecodeError('Unexpected end-group tag.')
+    except (IndexError, TypeError):
+      # Now ord(buf[p:p+1]) == ord('') gets TypeError.
+      raise message_mod.DecodeError('Truncated message.')
+    except struct.error as e:
+      raise message_mod.DecodeError(e)
+    return length   # Return this for legacy reasons.
+  cls.MergeFromString = MergeFromString
+
+  local_ReadTag = decoder.ReadTag
+  local_SkipField = decoder.SkipField
+  fields_by_tag = cls._fields_by_tag
+  message_set_decoders_by_tag = cls._message_set_decoders_by_tag
+
+  def InternalParse(self, buffer, pos, end):
+    """Create a message from serialized bytes.
+
+    Args:
+      self: Message, instance of the proto message object.
+      buffer: memoryview of the serialized data.
+      pos: int, position to start in the serialized data.
+      end: int, end position of the serialized data.
+
+    Returns:
+      Message object.
+    """
+    # Guard against internal misuse, since this function is called internally
+    # quite extensively, and its easy to accidentally pass bytes.
+    assert isinstance(buffer, memoryview)
+    self._Modified()
+    field_dict = self._fields
+    while pos != end:
+      (tag_bytes, new_pos) = local_ReadTag(buffer, pos)
+      field_decoder, field_des = message_set_decoders_by_tag.get(
+          tag_bytes, (None, None)
+      )
+      if field_decoder:
+        pos = field_decoder(buffer, new_pos, end, self, field_dict)
+        continue
+      field_des, is_packed = fields_by_tag.get(tag_bytes, (None, None))
+      if field_des is None:
+        if not self._unknown_fields:   # pylint: disable=protected-access
+          self._unknown_fields = []    # pylint: disable=protected-access
+        # pylint: disable=protected-access
+        (tag, _) = decoder._DecodeVarint(tag_bytes, 0)
+        field_number, wire_type = wire_format.UnpackTag(tag)
+        if field_number == 0:
+          raise message_mod.DecodeError('Field number 0 is illegal.')
+        # TODO: remove old_pos.
+        old_pos = new_pos
+        (data, new_pos) = decoder._DecodeUnknownField(
+            buffer, new_pos, wire_type)  # pylint: disable=protected-access
+        if new_pos == -1:
+          return pos
+        # TODO: remove _unknown_fields.
+        new_pos = local_SkipField(buffer, old_pos, end, tag_bytes)
+        if new_pos == -1:
+          return pos
+        self._unknown_fields.append(
+            (tag_bytes, buffer[old_pos:new_pos].tobytes()))
+        pos = new_pos
+      else:
+        _MaybeAddDecoder(cls, field_des)
+        field_decoder = field_des._decoders[is_packed]
+        pos = field_decoder(buffer, new_pos, end, self, field_dict)
+        if field_des.containing_oneof:
+          self._UpdateOneofState(field_des)
+    return pos
+  cls._InternalParse = InternalParse
+
+
+def _AddIsInitializedMethod(message_descriptor, cls):
+  """Adds the IsInitialized and FindInitializationError methods to the
+  protocol message class."""
+
+  required_fields = [field for field in message_descriptor.fields
+                           if field.label == _FieldDescriptor.LABEL_REQUIRED]
+
+  def IsInitialized(self, errors=None):
+    """Checks if all required fields of a message are set.
+
+    Args:
+      errors:  A list which, if provided, will be populated with the field
+               paths of all missing required fields.
+
+    Returns:
+      True iff the specified message has all required fields set.
+    """
+
+    # Performance is critical so we avoid HasField() and ListFields().
+
+    for field in required_fields:
+      if (field not in self._fields or
+          (field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE and
+           not self._fields[field]._is_present_in_parent)):
+        if errors is not None:
+          errors.extend(self.FindInitializationErrors())
+        return False
+
+    for field, value in list(self._fields.items()):  # dict can change size!
+      if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+        if field.label == _FieldDescriptor.LABEL_REPEATED:
+          if (field.message_type._is_map_entry):
+            continue
+          for element in value:
+            if not element.IsInitialized():
+              if errors is not None:
+                errors.extend(self.FindInitializationErrors())
+              return False
+        elif value._is_present_in_parent and not value.IsInitialized():
+          if errors is not None:
+            errors.extend(self.FindInitializationErrors())
+          return False
+
+    return True
+
+  cls.IsInitialized = IsInitialized
+
+  def FindInitializationErrors(self):
+    """Finds required fields which are not initialized.
+
+    Returns:
+      A list of strings.  Each string is a path to an uninitialized field from
+      the top-level message, e.g. "foo.bar[5].baz".
+    """
+
+    errors = []  # simplify things
+
+    for field in required_fields:
+      if not self.HasField(field.name):
+        errors.append(field.name)
+
+    for field, value in self.ListFields():
+      if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+        if field.is_extension:
+          name = '(%s)' % field.full_name
+        else:
+          name = field.name
+
+        if _IsMapField(field):
+          if _IsMessageMapField(field):
+            for key in value:
+              element = value[key]
+              prefix = '%s[%s].' % (name, key)
+              sub_errors = element.FindInitializationErrors()
+              errors += [prefix + error for error in sub_errors]
+          else:
+            # ScalarMaps can't have any initialization errors.
+            pass
+        elif field.label == _FieldDescriptor.LABEL_REPEATED:
+          for i in range(len(value)):
+            element = value[i]
+            prefix = '%s[%d].' % (name, i)
+            sub_errors = element.FindInitializationErrors()
+            errors += [prefix + error for error in sub_errors]
+        else:
+          prefix = name + '.'
+          sub_errors = value.FindInitializationErrors()
+          errors += [prefix + error for error in sub_errors]
+
+    return errors
+
+  cls.FindInitializationErrors = FindInitializationErrors
+
+
+def _FullyQualifiedClassName(klass):
+  module = klass.__module__
+  name = getattr(klass, '__qualname__', klass.__name__)
+  if module in (None, 'builtins', '__builtin__'):
+    return name
+  return module + '.' + name
+
+
+def _AddMergeFromMethod(cls):
+  LABEL_REPEATED = _FieldDescriptor.LABEL_REPEATED
+  CPPTYPE_MESSAGE = _FieldDescriptor.CPPTYPE_MESSAGE
+
+  def MergeFrom(self, msg):
+    if not isinstance(msg, cls):
+      raise TypeError(
+          'Parameter to MergeFrom() must be instance of same class: '
+          'expected %s got %s.' % (_FullyQualifiedClassName(cls),
+                                   _FullyQualifiedClassName(msg.__class__)))
+
+    assert msg is not self
+    self._Modified()
+
+    fields = self._fields
+
+    for field, value in msg._fields.items():
+      if field.label == LABEL_REPEATED:
+        field_value = fields.get(field)
+        if field_value is None:
+          # Construct a new object to represent this field.
+          field_value = field._default_constructor(self)
+          fields[field] = field_value
+        field_value.MergeFrom(value)
+      elif field.cpp_type == CPPTYPE_MESSAGE:
+        if value._is_present_in_parent:
+          field_value = fields.get(field)
+          if field_value is None:
+            # Construct a new object to represent this field.
+            field_value = field._default_constructor(self)
+            fields[field] = field_value
+          field_value.MergeFrom(value)
+      else:
+        self._fields[field] = value
+        if field.containing_oneof:
+          self._UpdateOneofState(field)
+
+    if msg._unknown_fields:
+      if not self._unknown_fields:
+        self._unknown_fields = []
+      self._unknown_fields.extend(msg._unknown_fields)
+
+  cls.MergeFrom = MergeFrom
+
+
+def _AddWhichOneofMethod(message_descriptor, cls):
+  def WhichOneof(self, oneof_name):
+    """Returns the name of the currently set field inside a oneof, or None."""
+    try:
+      field = message_descriptor.oneofs_by_name[oneof_name]
+    except KeyError:
+      raise ValueError(
+          'Protocol message has no oneof "%s" field.' % oneof_name)
+
+    nested_field = self._oneofs.get(field, None)
+    if nested_field is not None and self.HasField(nested_field.name):
+      return nested_field.name
+    else:
+      return None
+
+  cls.WhichOneof = WhichOneof
+
+
+def _Clear(self):
+  # Clear fields.
+  self._fields = {}
+  self._unknown_fields = ()
+
+  self._oneofs = {}
+  self._Modified()
+
+
+def _UnknownFields(self):
+  raise NotImplementedError('Please use the add-on feaure '
+                            'unknown_fields.UnknownFieldSet(message) in '
+                            'unknown_fields.py instead.')
+
+
+def _DiscardUnknownFields(self):
+  self._unknown_fields = []
+  for field, value in self.ListFields():
+    if field.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
+      if _IsMapField(field):
+        if _IsMessageMapField(field):
+          for key in value:
+            value[key].DiscardUnknownFields()
+      elif field.label == _FieldDescriptor.LABEL_REPEATED:
+        for sub_message in value:
+          sub_message.DiscardUnknownFields()
+      else:
+        value.DiscardUnknownFields()
+
+
+def _SetListener(self, listener):
+  if listener is None:
+    self._listener = message_listener_mod.NullMessageListener()
+  else:
+    self._listener = listener
+
+
+def _AddMessageMethods(message_descriptor, cls):
+  """Adds implementations of all Message methods to cls."""
+  _AddListFieldsMethod(message_descriptor, cls)
+  _AddHasFieldMethod(message_descriptor, cls)
+  _AddClearFieldMethod(message_descriptor, cls)
+  if message_descriptor.is_extendable:
+    _AddClearExtensionMethod(cls)
+    _AddHasExtensionMethod(cls)
+  _AddEqualsMethod(message_descriptor, cls)
+  _AddStrMethod(message_descriptor, cls)
+  _AddReprMethod(message_descriptor, cls)
+  _AddUnicodeMethod(message_descriptor, cls)
+  _AddContainsMethod(message_descriptor, cls)
+  _AddByteSizeMethod(message_descriptor, cls)
+  _AddSerializeToStringMethod(message_descriptor, cls)
+  _AddSerializePartialToStringMethod(message_descriptor, cls)
+  _AddMergeFromStringMethod(message_descriptor, cls)
+  _AddIsInitializedMethod(message_descriptor, cls)
+  _AddMergeFromMethod(cls)
+  _AddWhichOneofMethod(message_descriptor, cls)
+  # Adds methods which do not depend on cls.
+  cls.Clear = _Clear
+  cls.DiscardUnknownFields = _DiscardUnknownFields
+  cls._SetListener = _SetListener
+
+
+def _AddPrivateHelperMethods(message_descriptor, cls):
+  """Adds implementation of private helper methods to cls."""
+
+  def Modified(self):
+    """Sets the _cached_byte_size_dirty bit to true,
+    and propagates this to our listener iff this was a state change.
+    """
+
+    # Note:  Some callers check _cached_byte_size_dirty before calling
+    #   _Modified() as an extra optimization.  So, if this method is ever
+    #   changed such that it does stuff even when _cached_byte_size_dirty is
+    #   already true, the callers need to be updated.
+    if not self._cached_byte_size_dirty:
+      self._cached_byte_size_dirty = True
+      self._listener_for_children.dirty = True
+      self._is_present_in_parent = True
+      self._listener.Modified()
+
+  def _UpdateOneofState(self, field):
+    """Sets field as the active field in its containing oneof.
+
+    Will also delete currently active field in the oneof, if it is different
+    from the argument. Does not mark the message as modified.
+    """
+    other_field = self._oneofs.setdefault(field.containing_oneof, field)
+    if other_field is not field:
+      del self._fields[other_field]
+      self._oneofs[field.containing_oneof] = field
+
+  cls._Modified = Modified
+  cls.SetInParent = Modified
+  cls._UpdateOneofState = _UpdateOneofState
+
+
+class _Listener(object):
+
+  """MessageListener implementation that a parent message registers with its
+  child message.
+
+  In order to support semantics like:
+
+    foo.bar.baz.moo = 23
+    assert foo.HasField('bar')
+
+  ...child objects must have back references to their parents.
+  This helper class is at the heart of this support.
+  """
+
+  def __init__(self, parent_message):
+    """Args:
+      parent_message: The message whose _Modified() method we should call when
+        we receive Modified() messages.
+    """
+    # This listener establishes a back reference from a child (contained) object
+    # to its parent (containing) object.  We make this a weak reference to avoid
+    # creating cyclic garbage when the client finishes with the 'parent' object
+    # in the tree.
+    if isinstance(parent_message, weakref.ProxyType):
+      self._parent_message_weakref = parent_message
+    else:
+      self._parent_message_weakref = weakref.proxy(parent_message)
+
+    # As an optimization, we also indicate directly on the listener whether
+    # or not the parent message is dirty.  This way we can avoid traversing
+    # up the tree in the common case.
+    self.dirty = False
+
+  def Modified(self):
+    if self.dirty:
+      return
+    try:
+      # Propagate the signal to our parents iff this is the first field set.
+      self._parent_message_weakref._Modified()
+    except ReferenceError:
+      # We can get here if a client has kept a reference to a child object,
+      # and is now setting a field on it, but the child's parent has been
+      # garbage-collected.  This is not an error.
+      pass
+
+
+class _OneofListener(_Listener):
+  """Special listener implementation for setting composite oneof fields."""
+
+  def __init__(self, parent_message, field):
+    """Args:
+      parent_message: The message whose _Modified() method we should call when
+        we receive Modified() messages.
+      field: The descriptor of the field being set in the parent message.
+    """
+    super(_OneofListener, self).__init__(parent_message)
+    self._field = field
+
+  def Modified(self):
+    """Also updates the state of the containing oneof in the parent message."""
+    try:
+      self._parent_message_weakref._UpdateOneofState(self._field)
+      super(_OneofListener, self).Modified()
+    except ReferenceError:
+      pass