argparse subparsers not recognized

Question

I have the following test code:

import argparse
myparser = argparse.ArgumentParser(prog='test')
myparser.add_argument('mode', choices=['A', 'B'])
subparsers = myparser.add_subparsers()
a_parser = subparsers.add_parser('A')
b_parser = subparsers.add_parser('B')
a_parser.add_argument('frog',action='store')
b_parser.add_argument('toad',action='store')
print(myparser)
try:
    args = myparser.parse_args(['A', 'frogname'])
    print(args)
except ArgumentError as ae:
    print(ae)

When I run it I get the following:

ArgumentParser(prog='test', usage=None, description=None, formatter_class=<class 'argparse.HelpFormatter'>, conflict_handler='error', add_help=True)
usage: test [-h] {A,B} {A,B} ...
test: error: invalid choice: 'frogname' (choose from 'A', 'B')

I'm not sure why I'm getting multiple copies of the 'mode' argument or why my subparsers are being ignored.

user2201041 · Accepted Answer · 2018-11-28 16:50:53Z

If you are using mode to try to select the subparser, you don't need to do that. That's part of what add_parser() does for you.

myparser = argparse.ArgumentParser(prog='test')
# myparser.add_argument('mode', choices=['A', 'B'])  # Don't think you need this
subparsers = myparser.add_subparsers()
a_parser = subparsers.add_parser('A')
b_parser = subparsers.add_parser('B')
a_parser.add_argument('frog',action='store')
b_parser.add_argument('toad',action='store')

args = myparser.parse_args(['A', 'frogname'])
print(args)
>>> Namespace(frog='frogname')

If mode is something separate that you want to set in addition to choosing the subparser, you need to pass that argument separately

myparser = argparse.ArgumentParser(prog='test')
myparser.add_argument('mode', choices=['A', 'B'])
subparsers = myparser.add_subparsers()
a_parser = subparsers.add_parser('A')
b_parser = subparsers.add_parser('B')
a_parser.add_argument('frog',action='store')
b_parser.add_argument('toad',action='store')

args = myparser.parse_args(['A', 'A', 'frogname'])
print(args)
>>> Namespace(frog='frogname', mode='A')

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