argparse_loader.py

# -*- coding:utf-8 -*-
import argparse


class MixiedArgs(object):
    def __init__(self, args, defaults):
        self.args = args
        self.defaults = defaults

    def __getattr__(self, k):
        return getattr(self.args, k, None) or getattr(self.defaults, k)


class ObjectLikeDict(dict):
    __getattr__ = dict.get


class LoadJSONConfigAction(argparse.Action):
    def __call__(self, parser, namespace, val, option_string=None):
        import json

        if val.startswith("file://"):
            with open(val.lstrip("file://")) as rf:
                data = json.load(rf, object_pairs_hook=ObjectLikeDict)
        else:
            data = json.loads(val, object_pairs_hook=ObjectLikeDict)
        setattr(namespace, self.dest, data)


def make_parser():
    parser = argparse.ArgumentParser()
    parser.add_argument("--name")
    parser.add_argument("--message")
    parser.add_argument("--profile", action=LoadJSONConfigAction)
    return parser

if __name__ == "__main__":
    def run(args):
        print(args.message.format(name=args.name))

    parser = make_parser()

    class DefaultConfig:
        name = "foo"
        message = "{name}: hai"

    args = parser.parse_args(["--message", "{name}: hello"])
    run(MixiedArgs(args, DefaultConfig))

    args = parser.parse_args(["--message", "{name}: bye", "--profile", '{"name": "bar"}'])
    run(MixiedArgs(args, args.profile))

    args = parser.parse_args(["--profile=file://profile.json"])
    run(MixiedArgs(args, args.profile))

profile.json

{
  "name": "this-is-my-name",
  "message": "<message sender=\"{name}\">hello</message>"
}

foo: hello
bar: bye
<message sender="this-is-my-name">hello</message>