def make_basic_parser():
    parser = argparse.ArgumentParser(description='Basic parser (only username/password).', add_help=False)
    parser.add_argument('--username', type=str, help='Username to access database')
    parser.add_argument('--password', type=str, help='Password to access database')
    return parser


def alter_table_parser():
    parent = make_basic_parser()
    parser = argparse.ArgumentParser(description='Alter a table', parents=[parent])
    parser.add_argument('--table', type=str, help='Table to alter')
    return parser


if __name__ == "__main__":
    parser = alter_table_parser()
    args = parser.parse_args()
    print("Received arguments: %s" % (args))

$ python ./stack_055_A.py --username foo --password bar --table baz
Received arguments: Namespace(password='bar', table='baz', username='foo')