code: def __validate_path_parameters(self, field, path_parameters):
      
      for param in path_parameters:
        segment_list = param.split('.')
        if segment_list[0] != field.name:
          raise TypeError('Subfield %r can\'t come from field %r.'
                          % (param, field.name))
        self.__validate_simple_subfield(field.name, field, segment_list[1:])
docs: Verifies that all path parameters correspond to an existing subfield.
  
      Args:
        field: An instance of a subclass of messages.Field. Should be the root
            level property name in each path parameter in path_parameters. For
            example, if the field is called 'foo', then each path parameter should
            begin with 'foo.'.
        path_parameters: A list of Strings representing URI parameter variables.
  
      Raises:
        TypeError: If one of the path parameters does not start with field.name.