Load python config from json. Replace env vars templates with values

config_utils.py

def load_app_config(config_file_path):
    '''
    load json config file, example:
    {
        "query": {
            "port": 8000,
            "env1": "${ENV1:-default_value}",
            "env2": "${ENV2:-12}"
        }
    }
    :param config_file_path:
    :return:
    '''

    def _cast_to_type(s):
        try:
            return int(s)
        except ValueError:
            try:
                return float(s)
            except ValueError:
                return s

    def _substitude_env_vars(d):
        for key in d.keys():
            v = d.get(key)
            if isinstance(v, str):
                m = re.match('\${(\w+)\:-(\w+)}', v)
                if m:
                    env_name = m.group(1)
                    def_val = m.group(2)
                    env_val = os.environ.get(env_name)
                    if env_val is None:
                        env_val = _cast_to_type(def_val)
                    d[key] = env_val
            elif isinstance(v, dict):
                _substitude_env_vars(v)

    if os.path.isfile(config_file_path):
        with open(config_file_path, 'r') as f:
            app_config = json.load(f)
            _substitude_env_vars(app_config)
            return app_config
    else:
        raise Exception('Configuration file not found: '.format(config_file_path))