def GetMessages(self, files):
    # TODO(amauryfa): Fix the differences with MessageFactory.
    """Gets all registered messages from a specified file.

    Only messages already created and registered will be returned; (this is the
    case for imported _pb2 modules)
    But unlike MessageFactory, this version also returns already defined nested
    messages, but does not register any message extensions.

    Args:
      files (list[str]): The file names to extract messages from.

    Returns:
      A dictionary mapping proto names to the message classes.

    Raises:
      KeyError: if a file could not be found.
    """

    def _GetAllMessages(desc):
      """Walk a message Descriptor and recursively yields all message names."""
      yield desc
      for msg_desc in desc.nested_types:
        for nested_desc in _GetAllMessages(msg_desc):
          yield nested_desc

    result = {}
    for file_name in files:
      file_desc = self.pool.FindFileByName(file_name)
      for msg_desc in file_desc.message_types_by_name.values():
        for desc in _GetAllMessages(msg_desc):
          try:
            result[desc.full_name] = self._classes[desc]
          except KeyError:
            # This descriptor has no registered class, skip it.
            pass
    return result
Gets all registered messages from a specified file.

    Only messages already created and registered will be returned; (this is the
    case for imported _pb2 modules)
    But unlike MessageFactory, this version also returns already defined nested
    messages, but does not register any message extensions.

    Args:
      files (list[str]): The file names to extract messages from.

    Returns:
      A dictionary mapping proto names to the message classes.

    Raises:
      KeyError: if a file could not be found.
    
deps/protobuf/python/google/protobuf/symbol_database.py