How can python 2.x argparser get either one required argument or one optional?

Question

linux

How can python 2.x argparser get EITHER one required argument OR one optional?
That is, EITHER python @[email protected] is a required parameter
OR python @[email protected] is an optional parameter

Answer 1

What's the problem?

from argparse import ArgumentParser

parser = ArgumentParser(usage="Here is usagage")
parser.add_argument("positional",nargs="*")
parser.add_argument("--flag")

if __name__ == "__main__":
    args = parser.parse_args()
    if args.positional and not args.flag:
        print("i'm positional")
    elif args.flag and not args.flag:
        print ("i'm flag")
    else:
        raise Exception("RTFM")