code: def _add_message_file(arg_parser, help_text):
      
      arg_parser.add_argument('--msg-file',
                              type=argparse.FileType('r'),
                              help=help_text)
docs: Add mesage file argument with help_text to arg_parser.
      :param arg_parser: ArgumentParser parser to add this argument to.
      :param help_text: str: help text for this argument