How to use the pybase64.__main__.LicenseAction function in pybase64

def main(args=None):
    # main parser
    parser = argparse.ArgumentParser(
        prog=__package__,
        description=__package__ + ' command-line tool.')
    parser.add_argument(
        '-V', '--version',
        action='version',
        version=__package__ + ' ' + pybase64.get_version())
    parser.add_argument(
        '--license',
        action=LicenseAction,
        license=pybase64.get_license_text())
    # create sub-parsers
    subparsers = parser.add_subparsers(help='tool help')
    # benchmark parser
    benchmark_parser = subparsers.add_parser('benchmark', help='-h for usage')
    benchmark_parser.add_argument(
        '-d', '--duration',
        metavar='D',
        dest='duration',
        type=float,
        default=1.0,
        help='expected duration for a single encode or decode test')
    benchmark_parser.add_argument(
        'input',
        type=argparse.FileType('rb'),
        help='input file used for the benchmark')

def __init__(self,
                 option_strings,
                 license=None,
                 dest=argparse.SUPPRESS,
                 default=argparse.SUPPRESS,
                 help="show license information and exit"):
        super(LicenseAction, self).__init__(
            option_strings=option_strings,
            dest=dest,
            default=default,
            nargs=0,
            help=help)
        self.license = license