Using a decorator to simplify subcommand creation with argparse

cli.py

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"""

from argparse import ArgumentParser

cli = ArgumentParser()
subparsers = cli.add_subparsers(dest="subcommand")


def argument(*name_or_flags, **kwargs):
    """Convenience function to properly format arguments to pass to the
    subcommand decorator.

    """
    return (list(name_or_flags), kwargs)


def subcommand(args=[], parent=subparsers):
    """Decorator to define a new subcommand in a sanity-preserving way.
    The function will be stored in the ``func`` variable when the parser
    parses arguments so that it can be called directly like so::

        args = cli.parse_args()
        args.func(args)

    Usage example::

        @subcommand([argument("-d", help="Enable debug mode", action="store_true")])
        def subcommand(args):
            print(args)

    Then on the command line::

        $ python cli.py subcommand -d

    """
    def decorator(func):
        parser = parent.add_parser(func.__name__, description=func.__doc__)
        for arg in args:
            parser.add_argument(*arg[0], **arg[1])
        parser.set_defaults(func=func)
    return decorator


@subcommand()
def nothing(args):
    print("Nothing special!")


@subcommand([argument("-d", help="Debug mode", action="store_true")])
def test(args):
    print(args)


@subcommand([argument("-f", "--filename", help="A thing with a filename")])
def filename(args):
    print(args.filename)


@subcommand([argument("name", help="Name")])
def name(args):
    print(args.name)


if __name__ == "__main__":
    args = cli.parse_args()
    if args.subcommand is None:
        cli.print_help()
    else:
        args.func(args)

could the sudcommand() be expanded to support aliases?

Adding support for aliases can be accomplished by adding another argument to subcommand. Here's an example:

def subcommand(args=[], parent=subparsers, aliases=[]):

    def decorator(func):
        parser = parent.add_parser(func.__name__, description=func.__doc__, aliases=aliases)
        ...

@subcommand([argument("-d", help="Debug mode", action="store_true")], aliases=['t'])
def test(args):
    ...

Why doesn't this work with @functools.wraps? See https://stackoverflow.com/a/41377289/8652920 for reference. When I do this to the subcommand decorator, everything breaks.

Thanks for sharing!

A modified version for those who prefer dedicated decorator for each argument (more readable IMHO). Perhaps somewhat awkward by creating new attribute __arguments__ but hopefully someone may share a cleaner solution.

import argparse

cli = argparse.ArgumentParser()
subparsers = cli.add_subparsers(dest="command")


def command(*args, parent=subparsers, **kwargs):
    def decorator(func):
        parser = parent.add_parser(*args, **kwargs)
        parser.set_defaults(func=func)
        for arg in getattr(func, "__arguments__", []):
            parser.add_argument(*arg[0], **arg[1])
        return func

    return decorator


def argument(*name_or_flags, **kwargs):
    def decorator(func):
        if not hasattr(func, "__arguments__"):
            func.__arguments__ = []
        func.__arguments__.append((name_or_flags, kwargs))
        return func

    return decorator


@command(
    "nothing",
    help="help for nothing command",
)
def nothing_handler(_):
    print("Nothing special!")


@command(
    "the_command",
    help="help for the command",
)
@argument(
    "arg",
    type=str,
    help="random arg to provide",
)
@argument(
    "-f",
    "--flag",
    action="store_true",
    help="random flag to set",
)
def the_command_handler(args):
    print(f"running 'the_command' with arg: {args.arg}, flag: {args.flag},")


def main():
    args = cli.parse_args()
    if args.command is None:
        cli.print_help()
    else:
        args.func(args)


if __name__ == "__main__":
    main()