How to include regex choices in python ArgumentParser.add_argument()?

Question

How would I go about including regex expressions in the choices kwarg for Python's ArgumentParser.add_argument() method?

For example, lets say I wish to create my own custom mount program:

# file: my_mount.py
from argparse import ArgumentParser

# some simple choices to help illustrate 
option_choices = {'ro|rw', 'user=.*', 'do=[a-z]{1,10}', 'allow_other'}

if __name__ == '__main__':
    parser = ArgumentParser()
    parser.add_argument('-s', '--share', dest='share')
    parser.add_argument('-m', '--mount-point', dest='mnt_pt')
    parser.add_argument('-o', dest='options', action='append', 
                        choices=option_choices, 
                        help='Options for mounting - see choices '
                             'expressions set for valid options')

    args, _ = parser.parse_known_args()
    # do some fancy stuff to do with mounting filesystems...

With the idea that I could filter out valid options based on a simple set of regular expressions, especially as hand-coding in all possibilities is a chore e.g. {'do=nothing', 'do=something', 'do=anything'...}, but also handily retain the choices list when invoking python my_mount.py -h. My initial thoughts were to have a custom action, but this doesn't seem compatible with when specifying choices in add_argument()

You can't. You need to accept in any string and then do assert any(re.match(expr, opt) is not None for expr in option_choices for opt in args.options) or similar. Just add 'accepts: {}'.format(option_choices) to the help argument of --options. You don't need to rely on ArgParses automatic checks. — FHTMitchell
– FHTMitchell, Commented Feb 8, 2018 at 14:48

The Stupid Engineer · Accepted Answer · 2020-04-23 12:53:54Z

3

I was looking at a similar issue and settled on using type for validation instead.

This allows you to use a callable to perform validation instead. So instead of using choices, use type to specify a callable that does your regex match in there instead.

If you want to retain choices in a container somewhere then you could do that too. Alternatively you could define a custom container which validates input if you must use choices only.

answered Apr 23, 2020 at 12:53

The Stupid Engineer

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