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

Question

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 was using Python 3.2 here back in 2012.

It turns out that BooleanOptionalAction has been added in Python 3.9's version of argparse and solves this problem, and I've changed my accepted answer to the new one. But, other answers on this page should help if you're still using a Python prior to 3.9.

Answer 1

Well, none of the answers so far are quite satisfactory for a variety of reasons. So here is my own answer:

class ActionNoYes(argparse.Action):     def __init__(self, opt_name, dest, default=True, required=False, help=None):         super(ActionNoYes, self).__init__(['--' + opt_name, '--no-' + opt_name], dest, nargs=0, const=None, default=default, required=required, help=help)     def __call__(self, parser, namespace, values, option_string=None):         if option_string.starts_with('--no-'):             setattr(namespace, self.dest, False)         else:             setattr(namespace, self.dest, True) 

And an example of use:

>>> p = argparse.ArgumentParser() >>> p._add_action(ActionNoYes('foo', 'foo', help="Do (or do not) foo. (default do)")) ActionNoYes(option_strings=['--foo', '--no-foo'], dest='foo', nargs=0, const=None, default=True, type=None, choices=None, help='Do (or do not) foo. (default do)', metavar=None) >>> p.parse_args(['--no-foo', '--foo', '--no-foo']) Namespace(foo=False) >>> p.print_help() usage: -c [-h] [--foo]  optional arguments:   -h, --help       show this help message and exit   --foo, --no-foo  Do (or do not) foo. (default do) 

Unfortunately, the _add_action member function isn't documented, so this isn't 'official' in terms of being supported by the API. Also, Action is mainly a holder class. It has very little behavior on its own. It would be nice if it were possible to use it to customize the help message a bit more. For example saying --[no-]foo at the beginning. But that part is auto-generated by stuff outside the Action class.