How to parse optional arguments using python argparse?

Question

I am trying to parse a command line like this

cmd {command [COMMAND_OPTS]}

cmd a {1,2}

cmd b

cmd c

Among the commands{a,b,c}, when the command is "a", there might be a COMMAND_OPTS(choices) for "a", say{1,2}, b or c won't have any arguments. And here is what I tried:

import argparse

if __name__ == "__main__":
parser = argparse.ArgumentParser()
parser.add_argument('-cmd', nargs = '+', choices = ['a', 'b', 'c'])
# sub_parser = parser.add_subparsers()
# parse_a = sub_parser.add_parser('a')
# parser_a.add_argument("a", default = "1", choices = ["1", "2"])
args = parser.parse_args()
if args.cmd:
    print args.cmd

How to parse this with Python Argparse? It seems the subparser is not intended for this problem..

Thanks,

Please provide a Minimal, Complete, and Verifiable example of the problem you are experiencing. You need to make an attempting at solving this yourself so that we have something to debug. Otherwise, you may need to hire someone to do the job for you. — Noctis Skytower
– Noctis Skytower, Commented Feb 18, 2016 at 16:28

hpaulj · Accepted Answer · 2016-02-18 17:26:09Z

3

Put all the commands in the subparsers

parser = argparse.ArgumentParser()
sub_parser = parser.add_subparsers(dest='cmd')
parser_a = sub_parser.add_parser('a')
parser_a.add_argument("a", choices = ["1", "2"])
parser_b = sub_parser.add_parser('b')
parser_c = sub_parser.add_parser('c')
args = parser.parse_args()

args.cmd should end up being one of a,b,c. And if given a is should have a args.a attribute with value '1' or '2'. That argument is required so it doesn't make sense to specify a default.

From an interactive ipython shell:

In [13]: parser.parse_args(['b'])
Out[13]: Namespace(cmd='b')
In [14]: parser.parse_args(['c'])
Out[14]: Namespace(cmd='c')
In [15]: parser.parse_args(['a','1'])
Out[15]: Namespace(a='1', cmd='a')

edited Feb 18, 2016 at 17:26

answered Feb 18, 2016 at 17:20

hpaulj

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