arseparse

Arseparse is a simple Python utility/micro framework for writing command line interfaces. It provides some functionality around argparse to dispatch a command handler and pre-process its arguments.

The main pattern that it can help with is the following:

<entrypoint> root_args... command_name command_args...

For example:

<entrypoint> config.ini create_user foo@bar.xyz s3cr3t

Would execute this handler:

@parser.register_dec([Option('username', type=str), Option('secret', type=str)])
def create_user(username, secret, user_svc, **kwargs):
    user_svc.create_user(username, secret)

Where user_svc argument depends on the config root argument. More on that later.

Installation:

pip install arseparse

Basic usage (without root args):

from arseparse import Parser, Option


parser = Parser()


# register handler
@parser.register_dec([Option('value', type=int)])
def cube(value):
    return value**3


# register without a decorator
parser.register('square', lambda value: value**2, [Option('value', type=int)])


# register a command with no args
parser.register('ping', lambda: 'pong')


if __name__ == '__main__':
    sys.exit(parser.run())

Execute your entry_point or the file directly: your-entrypoint[.py] square 2

Common Usage

A more common scenario is to pass a config file as the first argument, parse it, create objects depend on the configuration, and pass those along to the handler. The root_options and bootstrap constructor args to Parser allow us to do this:

from arseparse import Parser, Option
import myapp


root_options = [Option('config', type=str, help='path to ini file')]


# this lets us process/modify the kwargs before we execute the callable.
def bootstrap(**kwargs):
    config_uri = kwargs.pop('config')
    settings = myapp.parse_app_config(config_uri)
    dbsession = myapp.get_sessionmaker(settings)()
    user_svc = myapp.UserService(dbsession)
    kwargs.update(dict(settings=settings, dbsession=dbsession, user_svc=user_svc))
    return kwargs


parser = Parser(root_options, bootstrap)


@parser.register_dec([Option('username', type=str), Option('secret', type=str)])
def create_user(username, secret, user_svc, **kwargs):
    user_svc.create_user(username, secret)
    
 
@parser.register_dec([Option('user_id', type=int)])
def ban_user(user_id, user_svc, **kwargs):
    user_svc.ban_user(user_id)


@parser.register_dec()
def print_settings(settings, **kwargs):
    print(settings)

You can now provide the path to a config file as the first argument: your-entrypoint[.py] config.ini ban_user 23

Recipes

Another common requirement is to be able to jump into a shell where some objects have been preconfigured for us. Here's a simple recipe for that.

@parser.register_dec()
def shell(**kwargs):
    import IPython
    IPython.embed(user_ns=kwargs)

Calling your-entrypoint.py config.ini shell will drop you in an ipython shell where dbsession, settings and user_svc are available.