Integration with argparse

[mheppner]

I have a use-case where I need to support both command-line arguments, as well as environment variables. This pattern ends up looking like this:

def parse_env():
    env = Env()
    return {
        'my_option': env.str('MY_OPTION', default='value'),
        'positional': env.str('POSITIONAL')
        'many_inputs': env.list('MANY_INPUTS')
    }

def parse_cli():
    parser = argparse.ArgumentParser()
    parser.add_argument('-m', '--my-option', default='value')
    parser.add_argument(dest='positional')
    parser.add_argument(dest='many_inputs', nargs='+')
    return vars(parser.parse_args())

if __name__ == '__main__':
    if os.environ.get('USE_ENV'):
        args = parse_env()
    else:
        args = parse_cli()

    do_something(**args)

Is there a better pattern for this? There's a lot of duplicate logic, making sure both variables are the same and defaults match. Could this be a feature request to add this to argparse, maybe with a subclass?

I'm thinking something like this:

from environs import EnvArgumentParser
parser = EnvArgumentParser(
    env_prefix='MY_PREFIX_'  # this would be neat
)
parser.add_argument('-m', '--my-option', default='value', env_name='MY_OPTION')
parser.add_argument(dest='positional', env_name='CUSTOM_NAME')
parser.add_argument(dest='many_inputs', nargs='+')  # default env_name to MANY_INPUTS

Thoughts? If you think this would be useful for this library, I can try working on it. I don't know the internals of argparse very well though.

[sloria]

The EnvArgumentParser idea seems neat, but I think it's outside the scope of this library. Would definitely be cool to see as a separate package, though. Thanks for the suggestion.