def add_verbosity_argument(parser, default=0):
    """Add a verbosity argument to parser.

    Note:
      The argument is '-v' or '--verbosity'.
      Add multiple '-v' arguments, e.g. '-vv' or '-vvv' to
      increase the level of verbosity.

    Args:
      parser: A argparse object.
      default: The default level, defaults to 0.
    """
    parser.add_argument('-v', '--verbosity', help='Set level of verbosity.',
        action='count', default=default)
