argfmt.py

import argparse

class CustomHelpFormatter(argparse.HelpFormatter):
    def _format_action_invocation(self, action: argparse.Action) -> str:
        if not action.option_strings:
            default = self._get_default_metavar_for_positional(action)
            metavar, = self._metavar_formatter(action, default)(1)
            return metavar

        else:
            parts = []

            # if the Optional doesn't take a value, format is:
            #    -s, --long
            if action.nargs == 0:
                parts.extend(action.option_strings)

            # if the Optional takes a value, format is:
            #    -s, --long ARGS
            else:
                default = self._get_default_metavar_for_optional(action)
                args_string = self._format_args(action, default)
                for option_string in action.option_strings[:-1]:
                    parts.append('%s' % (option_string))
                parts.append('%s %s' % (action.option_strings[-1], args_string))

            return ', '.join(parts)