Parse arguments outside of main so we can have a custom entrypoint

[maerteijn]

With this pull request it becomes possible to write a custom entrypoint with a different argument parser or another source of arguments (for example a config file). Now this is almost impossible without monkey patching or duplicating a lot of code.

A custom entrypoint could looks like this:

import sys

from dramatiq.cli import argument_parser, main


def my_entrypoint():
    args = ['my.module:broker', 'my.module.actors', '-Q', 'myqueue']
    parsed_args = argument_parser().parse_args(args)
    return main(parsed_args)

if __name__ == "__main__":
    sys.exit(my_entrypoint())

Changing the existing arguments or adding extra ones will be much simpler then as well. Could also simplify the dramatiq-django integration by calling the python module directly instead of os.execvp.

[Bogdanp]

Thanks! Please make a commit adding yourself to the contributors file.

[Bogdanp]

Is there a particular reason to change this function? Do you plan to augment the argument parser?

[maerteijn]

Wlel, the function first parsed the arguments and returned them. Now it returns the argument parser itself.

It think it should be clear what the function is doing, that's why I suggest to change the name.

[Bogdanp]

Right, I wasn't asking about the name specifically. I was asking about the reasoning behind changing it to return the parser. :D

[maerteijn]

Oh, sorry for the misunderstanding 😃 I have two existing scenarios in our project where we would like to pass the arguments to the main function instead of parsing the arguments inside it.

1. A custom entrypoint (console_script) with predefined arguments, see the example in the description of this pull request
2. A custom entrypoint (console_script) which does not parse the arguments from the commandline but from a configuration file deployed with our configuration manager

Now I have to mokeypatch the main function in cli.py to do so because there the parsing happens.

[Bogdanp]

Thanks! I made a couple small changes and merged this with rebase. I'll cut a release later today.