[FIXED] In Python argparse, is it possible to have paired --no-something/--something arguments?

Issue

I'm writing a program in which I would like to have arguments like this:

--[no-]foo   Do (or do not) foo. Default is do.

Is there a way to get argparse to do this for me?

I'm using Python 3.2

Solution

I modified the solution of @Omnifarious to make it more like the standard actions:

import argparse

class ActionNoYes(argparse.Action):
    def __init__(self, option_strings, dest, default=None, required=False, help=None):

        if default is None:
            raise ValueError('You must provide a default with Yes/No action')
        if len(option_strings)!=1:
            raise ValueError('Only single argument is allowed with YesNo action')
        opt = option_strings[0]
        if not opt.startswith('--'):
            raise ValueError('Yes/No arguments must be prefixed with --')

        opt = opt[2:]
        opts = ['--' + opt, '--no-' + opt]
        super(ActionNoYes, self).__init__(opts, dest, nargs=0, const=None, 
                                          default=default, required=required, help=help)
    def __call__(self, parser, namespace, values, option_strings=None):
        if option_strings.startswith('--no-'):
            setattr(namespace, self.dest, False)
        else:
            setattr(namespace, self.dest, True)

You can add the Yes/No argument as you would add any standard option. You just need to pass ActionNoYes class in the action argument:

parser = argparse.ArgumentParser()
parser.add_argument('--foo', action=ActionNoYes, default=False)

Now when you call it:

>> args = parser.parse_args(['--foo'])
Namespace(foo=True)
>> args = parser.parse_args(['--no-foo'])
Namespace(foo=False)
>> args = parser.parse_args([])
Namespace(foo=False)  

Answered By - btel