Hack to enable Gnu-style long options in python's argparse

gnu_argparse.py

#!/usr/bin/python3
import argparse
import inspect

class GnuStyleLongOption(argparse._StoreConstAction):
    def __init__(self, **kw):
        self._real_option_strings = kw['option_strings']
        opts = []
        for option_string in self._real_option_strings:
            opts.append(option_string)
            for choice in kw['choices']:
                opts.append(f'{option_string}={choice}')
        kw['option_strings'] = opts
        self.choices = kw.pop('choices')
        help_choices = [f"'{choice}'" for choice in self.choices]
        kw['help'] += f"; {kw['metavar']} is {', or '.join([', '.join(help_choices[:-1]), help_choices[-1]])}"
        super(GnuStyleLongOption, self).__init__(**kw)

    def __getattribute__(self, attr):
        caller_is_argparse_help = False
        for frame in inspect.stack():
            if frame.function == 'format_help' and frame.filename.endswith('argparse.py'):
                caller_is_argparse_help = True
                break

        if caller_is_argparse_help:
            if attr == 'option_strings':
                return [f'{i}[=WHEN]' for i in self._real_option_strings]
            if attr == 'nargs':
                return 0
            if attr == 'metavar':
                return None

        return super(GnuStyleLongOption, self).__getattribute__(attr)

    def __call__(self, parser, namespace, values, option_string=None):
        setattr(namespace, self.dest, self.const if '=' not in option_string else option_string[option_string.find('=') + 1:])

p = argparse.ArgumentParser()
p.add_argument('--color', '--colour', action=GnuStyleLongOption, choices=['always', 'never', 'auto'], const='always', default='auto', help='use markers to highlight whatever we want', metavar='WHEN')
p.add_argument('filenames', metavar='filename', nargs='*', help='file to process')
args = p.parse_args()

print(f'color = {args.color}, filenames = {args.filenames}')