Using a decorator to simplify subcommand creation with argparse

cli.py

"""This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to <http://unlicense.org/>

"""

from argparse import ArgumentParser

cli = ArgumentParser()
subcommands = { "root": { "parser": cli, "subparser": 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=root, command=None, aliaes=[], subparser=False):
    """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):
        if name is None:
            entry = func.__name__
        else:
            entry = name
        parser = subcommands[parent]["subparser"].add_parser(entry, description=func.__doc__, help=func.__doc__, aliases=aliases)
        parser.set_defaults(func=func)
        subcommands[func.__name__] = { "parser": parser }
        if subparser:
            # Use `func.__name__` since it is globally unique
            subcommands[func.__name__]["subparser"] = parser.add_subparsers(dest='subcommand')
        for arg in args:
            parser.add_argument(*arg[0], **arg[1])
    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 'func' not in args:
        cli.print_help()
    else:
        args.func(args)