parser = ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.set_defaults(mode='insert')
group.add_argument('--delete', action='store_const', dest='mode', const=
    'delete')
group.add_argument('--update', action='store_const', dest='mode', const=
    'update')
group.add_argument('--insert', action='store_const', dest='mode', const=
    'insert')
parser.add_argument('value', nargs='?')
args = parser.parse_args()
How to include one positional argument into argparse mutually exclusive group?