Parsing multiple subcommands at once using parse_known_args

Question

import argparse
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(help='config command help')

# create parser for config command 
parser_config = subparsers.add_parser('config', help='config help')
parser_config.add_argument('--configname', required=True, nargs=1)
parser_config.add_argument('--login', required=True, nargs=1)
parser_config.add_argument('--password', required=True, nargs=1)

parser_config1 = subparsers.add_parser('config1', help='config help')
parser_config1.add_argument('--configname', required=True, nargs=1)
parser_config1.add_argument('--login', required=True, nargs=1)
parser_config1.add_argument('--password', required=True, nargs=1)


rest = 'config --configname name1 --login abc1 --password def1 config1 --configname name2 --login abc2 --password def2'.split()

print(rest)
while rest:
        args,rest =  parser.parse_known_args(rest)
        argslist.append(args)
        print(args, rest)

Gives:

$ python3 create_config.py 
['config', '--configname', 'name1', '--login', 'abc1', '--password', 'def1', 'config1', '--configname', 'name2', '--login', 'abc2', '--password', 'def2']
Namespace(configname=['name2'], login=['abc2'], password=['def2']) ['config1'] [Namespace(configname=['name2'], login=['abc2'], password=['def2'])]
usage: create_config.py config1 [-h] --configname CONFIGNAME --login LOGIN
                                --password PASSWORD
create_config.py config1: error: the following arguments are required: --configname, --login, --password

I was hoping to see

['config', '--configname', 'name1', '--login', 'abc1', '--password', 'def1', 'config1', '--configname', 'name2', '--login', 'abc2', '--password', 'def2']
Namespace(configname=['name1'], login=['abc1'], password=['def1']) ['config1', '--configname', 'name2', '--login', 'abc2', '--password', 'def2']
Namespace(configname=['name2'], login=['abc2'], password=['def2']) []

How can I accomplish this ?

hpaulj · Accepted Answer · 2018-05-13 21:53:33Z

2

The config subparser gets:

['--configname', 'name1', '--login', 'abc1', '--password', 'def1', 'config1', '--configname', 'name2', '--login', 'abc2', '--password', 'def2']

It parses

['--configname', 'name1', '--login', 'abc1', '--password', 'def1']

as expected. It then sees config1, which it can't handle (no positionals). It puts that in the extras list, and continues to parse the rest

['--configname', 'name2', '--login', 'abc2', '--password', 'def2']

That overwrites the previous optional's values, which is what you end up seeing in the args.

I think that if the two subparsers took different flags, then this approach would work. I think issues like this were explored in the links to your previous question, but I'd have to study them to be sure.

Anyways, parse_known_args doesn't just quit when it encounters a string it can't parse. Like the regular parse_args it tries to handle the whole list, only it returns leftovers as a list rather than raise an error. And repeated optionals are allowed, even if they don't don't anything useful (unless defined as append actions).

edited May 13, 2018 at 21:53

answered May 13, 2018 at 21:47

hpaulj

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1 Comment

Ankur Agarwal Over a year ago

I have been looking for a way to correctly handle such argument parsing. I will further look at other answers in the links provided. Thanks

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