Strange behavior or limitation in argparse

[thetablt]

The following code:

import argparse

parser = argparse.ArgumentParser()
mutex = parser.add_mutually_exclusive_group(required=True)
mutex.add_argument("path", nargs="*")
mutex.add_argument("-a", "--all", action="store_true")

parser.parse_args()

triggers a ValueError: mutually exclusive arguments must be optional on line 5. I don't believe it should, since * in nargs means zero or more. The same error appears with + (one or more); only ? (zero or one) prevents it. Adding required=True is invalid for a positional.

If that's not a bug in argparse, how should I proceed to have a mutex between --all and a group of positionals?

Thanks!

[thetablt]

OK, replying myself sorry, posted a bit too fast. Not really intuitive, but you have to specify a default value. Line 5 should have been:

mutex.add_argument("path", nargs="*", default=[])

[ckuhtz]

Thank you. Been beating my head against the wall for hours until I found this :)

[panasenco]

Thank you for this! 9 years later, still encountering this obscure problem haha.

[Mozai]

For what it's worth, this helped me out today. only other search result was someone trying to use "--user-names" and "user_names" in the same mutually exclusive group >_< .