example of a argparse optional

Example 1: python argument parser default value

parser.add_argument("-v", "--verbose", action="store_true",
                    default="your default value", help="verbose output")

Example 2: argparse accept only few options

...
parser.add_argument('--val',
                    choices=['a', 'b', 'c'],
                    help='Special testing value')

args = parser.parse_args(sys.argv[1:])