args-overload

#!/bin/python3
import argparse


class OverloadAction(argparse.Action):
    class OverloadParser(argparse.ArgumentParser):
        def exit(self, status = 0, message = None):
            raise argparse.ArgumentError(None, message)

        def _print_message(self, message, file = None):
            pass

    class HelpAction(argparse.Action):
        def __call__(self, *args, **kwargs):
            self.help.print_help()
            self.help.exit()

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        assert self.nargs == argparse.REMAINDER # XXX FIXME: error better
        self._parsers = []

    def add_parser(self, **kwargs):
        self._parsers.append(_parser := self.OverloadParser(**kwargs, add_help = False))
        return _parser

    def __call__(self, parser, namespace, values, option_string = None):
        unknowns = []

        for _parser in self._parsers:
            # XXX FIXME: explain
            _parser.add_argument("--help", "-h", action = self.HelpAction, help = parser, nargs = 0, dest = argparse.SUPPRESS)

            try:
                known, unknown = _parser.parse_known_args(values)
            except argparse.ArgumentError:
                continue
            else:
                if not unknown:
                    setattr(namespace, self.dest, known)
                    return
                else:
                    unknowns.append(unknown)
        else:
            # XXX FIXME: commentary
            if not unknowns:
                unknowns.append(values)

        # XXX FIXME: show actual usage patterns associated with each unknowns
        parser.error("unrecognized arguments for every usage pattern: %s" % ", ".join("[%s]" % " ".join(x) for x in unknowns))


parser = argparse.ArgumentParser(prog='proggy', usage="%(prog)s <xyz>")
overloads = parser.add_argument("xyz", nargs=argparse.REMAINDER, action=OverloadAction, help="TKTK")

x = overloads.add_parser()
x.set_defaults(__which__ = "x")
x.add_argument("letter", choices=["a", "b", "c"])

y = overloads.add_parser()
y.set_defaults(__which__ = "y")
y.add_argument("number", type=int)

print(parser.parse_args())