Use Python click command to invoke a class method with variadic arguments

Question

I have a class that gets initialized with a previously unknown number of arguments and I want it to be done on CLI using Python's click package. My issue is that I can't manage to initialize it and run a click command:

$ python mycode.py arg1 arg2 ... argN click_command

Setting a defined number of arguments, like nargs=5, solves the issue of missing command but obligates me to input 5 arguments before my command. With variadic arguments like nargs=-1, click doesn't recognize click_command as a command.

How can I input n-many arguments, and then run the command using click?

import click

class Foo(object):
    def __init__(self, *args):
        self.args = args

    def log(self):
        print('self.args:', self.args)

pass_foo = click.make_pass_decorator(Foo)

@click.group()
@click.argument('myargs', nargs=-1)
@click.pass_context
def main(ctx, myargs):
    ctx.obj = Foo(myargs)
    print("arguments: ", myargs)

@main.command()
@pass_foo
def log(foo):
    foo.log()

main()

I expect to be able to run a click command after passing n-many args to my Foo() class, so I can initialize it and run its log() method as a CLI command, but the output is:

Error: Missing command

Stephen Rauch · Accepted Answer · 2019-02-15 04:52:03Z

3

I am not entirely sure what you are trying to do is the best way to approach this problem. I would think that placing the variadic arguments after the command would be a bit more logical, and would definitely more align with the way click works. But, you can do what you are after with this:

Custom Class:

class CommandAfterArgs(click.Group):

    def parse_args(self, ctx, args):
        parsed_args = super(CommandAfterArgs, self).parse_args(ctx, args)
        possible_command = ctx.params['myargs'][-1]
        if possible_command in self.commands:
            ctx.protected_args = [possible_command]
            ctx.params['myargs'] = ctx.params['myargs'][:-1]

        elif possible_command in ('-h', '--help'):
            if len(ctx.params['myargs']) > 1 and \
                    ctx.params['myargs'][-2] in self.commands:
                ctx.protected_args = [ctx.params['myargs'][-2]]
                parsed_args = ['--help']
                ctx.params['myargs'] = ctx.params['myargs'][:-2]
                ctx.args = [possible_command]

        return parsed_args

Using Custom Class:

Then to use the custom class, pass it as the cls argument to the group decorator like:

@click.group(cls=CommandAfterArgs)
@click.argument('myargs', nargs=-1)
def main(myargs):
    ...

Test Code:

import click

class Foo(object):
    def __init__(self, *args):
        self.args = args

    def log(self):
        print('self.args:', self.args)


pass_foo = click.make_pass_decorator(Foo)


@click.group(cls=CommandAfterArgs)
@click.argument('myargs', nargs=-1)
@click.pass_context
def main(ctx, myargs):
    ctx.obj = Foo(*myargs)
    print("arguments: ", myargs)


@main.command()
@pass_foo
def log(foo):
    foo.log()


if __name__ == "__main__":
    commands = (
        'arg1 arg2 log',
        'log --help',
        '--help',
    )

    import sys, time

    time.sleep(1)
    print('Click Version: {}'.format(click.__version__))
    print('Python Version: {}'.format(sys.version))
    for cmd in commands:
        try:
            time.sleep(0.1)
            print('-----------')
            print('> ' + cmd)
            time.sleep(0.1)
            main(cmd.split())

        except BaseException as exc:
            if str(exc) != '0' and \
                    not isinstance(exc, (click.ClickException, SystemExit)):
                raise

Results:

Click Version: 6.7
Python Version: 3.6.3 (v3.6.3:2c5fed8, Oct  3 2017, 18:11:49) [MSC v.1900 64 bit (AMD64)]
-----------
> arg1 arg2 log
arguments:  ('arg1', 'arg2')
self.args: ('arg1', 'arg2')
-----------
> log --help
arguments:  ()
Usage: test.py log [OPTIONS]

Options:
  --help  Show this message and exit.
-----------
> --help
Usage: test.py [OPTIONS] [MYARGS]... COMMAND [ARGS]...

Options:
  --help  Show this message and exit.

Commands:
  log

answered Feb 15, 2019 at 4:52

Stephen Rauch♦

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3 Comments

vassis Over a year ago

Thank you for your very nice answer, @stephen. If I place the variadic arguments after subcommands, aligning with the way click works as you are suggesting, I won't be able to initialize Foo() class on main() group command, in order to create an instance of Foo() to be used by its subcommands. The only way I have figured out how to run a subcommand followed by args at this Foo(*args) scenario was to instantiate it inside every subcommand. So is this the right way to do it? Is it useless trying to apply click on a class like Foo(*args)?

Stephen Rauch Over a year ago

I believe your use case can be handled as you desire. Suggest generating another question, with that as the specific problem you are trying to solve via click. Also I vaguely remember answering something similar already here on SO. maybe here

vassis Over a year ago

@StephenRauch you have done a similar answer indeed and with that I could answer my question by myself. Thank you.

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