def testDefaultValueForCustomMessages(self):
    """Check the value returned by non-existent fields."""
    def _CheckValueAndType(value, expected_value, expected_type):
      self.assertEqual(value, expected_value)
      self.assertIsInstance(value, expected_type)

    def _CheckDefaultValues(msg):
      try:
        int64 = long
      except NameError:  # Python3
        int64 = int
      try:
        unicode_type = unicode
      except NameError:  # Python3
        unicode_type = str
      _CheckValueAndType(msg.optional_int32, 0, int)
      _CheckValueAndType(msg.optional_uint64, 0, (int64, int))
      _CheckValueAndType(msg.optional_float, 0, (float, int))
      _CheckValueAndType(msg.optional_double, 0, (float, int))
      _CheckValueAndType(msg.optional_bool, False, bool)
      _CheckValueAndType(msg.optional_string, u'', unicode_type)
      _CheckValueAndType(msg.optional_bytes, b'', bytes)
      _CheckValueAndType(msg.optional_nested_enum, msg.FOO, int)
    # First for the generated message
    _CheckDefaultValues(unittest_pb2.TestAllTypes())
    # Then for a message built with from the DescriptorPool.
    pool = descriptor_pool.DescriptorPool()
    pool.Add(descriptor_pb2.FileDescriptorProto.FromString(
        unittest_import_public_pb2.DESCRIPTOR.serialized_pb))
    pool.Add(descriptor_pb2.FileDescriptorProto.FromString(
        unittest_import_pb2.DESCRIPTOR.serialized_pb))
    pool.Add(descriptor_pb2.FileDescriptorProto.FromString(
        unittest_pb2.DESCRIPTOR.serialized_pb))
    message_class = message_factory.MessageFactory(pool).GetPrototype(
        pool.FindMessageTypeByName(
            unittest_pb2.TestAllTypes.DESCRIPTOR.full_name))
    _CheckDefaultValues(message_class())
Check the value returned by non-existent fields.
deps/protobuf/python/google/protobuf/internal/descriptor_pool_test.py