config.json

{
	"option_1": true,
	"option_2": "test"
}

config_template.py

#!/usr/bin/env python

import json
import os

TEMPLATE_SAMPLE = { 'option_1': 'bool', 'option_2': 'str', 'option_3': 'int' }

class Options:
    def __init__(self,
            filename='config.json',
            template = TEMPLATE_SAMPLE):
        self.template = template
        if (os.path.exists(filename)):
            with open(filename) as f:
                self.__import_dict(json.load(f))

    def __import_attr(self, key, value):
        if (value is None):
            return
        if (isinstance(value, eval(self.template[key]))):
            setattr(self, key, value)
        else:
            raise ValueError("invalid type")

    def __import_dict(self, d):
        for key in self.template.keys():
            self.__import_attr(key, d.get(key))

    def import_opt(self, o):
        for key in self.template.keys():
            if (hasattr(o, key)):
                self.__import_attr(key, getattr(o, key))

if __name__ == '__main__':
    import argparse

    opt = Options()
    print(vars(opt))

    parser = argparse.ArgumentParser()
    parser.add_argument('-1', '--option_1', type=bool) 
    parser.add_argument('-2', '--option_2', type=str)
    parser.add_argument('-3', '--option_3', type=int)
    args = parser.parse_args()
    print(vars(args))

    opt.import_opt(args)
    print(vars(opt))