Python argparse: command-line argument that can be either named or positional

Question

I am trying to make a Python program that uses the argparse module to parse command-line options.

I want to make an optional argument that can either be

Answer 1

Here is a solution that I think does everything you want:

import argparse
if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument("-u", "--user-name", default="admin")
    # Gather all extra args into a list named "args.extra"
    parser.add_argument("extra", nargs='*')
    args = parser.parse_args()
    # Set args.user_name to first extra arg if it is not given and len(args.extra) > 0
    if args.user_name == parser.get_default("user_name") and args.extra:
        args.user_name = args.extra.pop(0)
    print args

If you run myScript -u batman or myScript --user-name=batman, args.user_name is set to 'batman'. If you do myScript batman, args.user_name is again set to 'batman'. And finally, if you just do myScript, args.user_name is set to 'admin'.

Also, as an added bonus, you now have all of the extra arguments that were passed to the script stored in args.extra. Hope this helps.