[Python Config Parser Compatible With Environment Var] Get config from config file or environment variables. The priority order of config is: Config file > Environment > default_value. #python #configparser #env

config.py

import os
import configparser


class Config:
    """ Get config from config file or environment variables.
    The priority order of config is: Config file > Environment > default_value.
    The env var is composed by: [SECTION]_[OPTION]
    For example:
    get_or_else('smtp', 'BIND_ADDRESS', '127.0.0.1')
    => os.environ.get('SMTP_BIND_ADDRESS', '127.0.0.1')
    """
    config = configparser.ConfigParser()

    BOOLEAN_STATES = {'1': True, 'yes': True, 'true': True, 'on': True,
                      '0': False, 'no': False, 'false': False, 'off': False}

    @staticmethod
    def init_config(file):
        if file:
            Config.config.read_file(file)

    @staticmethod
    def get_or_else(section, option, default_value):
        if Config.config.has_option(section, option):
            return Config.config.get(section, option,
                                     fallback=default_value)
        else:
            return os.environ.get('_'.join([section.upper(), option]),
                                  default_value)

    @staticmethod
    def getint_or_else(section, option, default_value):
        if Config.config.has_option(section, option):
            return Config.config.getint(section, option,
                                        fallback=default_value)
        else:
            return Config._get_conv_env_or_else(section, option,
                                                int, default_value)

    @staticmethod
    def getfloat_or_else(section, option, default_value):
        if Config.config.has_option(section, option):
            return Config.config.getfloat(section, option,
                                          fallback=default_value)
        else:
            return Config._get_conv_env_or_else(section, option,
                                                float, default_value)

    @staticmethod
    def getboolean_or_else(section, option, default_value):
        if Config.config.has_option(section, option):
            return Config.config.getboolean(section, option,
                                            fallback=default_value)
        else:
            return Config._get_conv_env_or_else(section, option,
                                                Config._convert_to_boolean,
                                                default_value)

    @staticmethod
    def _get_conv_env_or_else(section, option, conv, default_value):
        return conv(os.environ.get('_'.join([section.upper(), option.upper()]),
                                   default_value))

    @staticmethod
    def _convert_to_boolean(value):
        """Return a boolean value translating from other types if necessary.
        """
        if value.lower() not in Config.BOOLEAN_STATES:
            raise ValueError('Not a boolean: %s' % value)
        return Config.BOOLEAN_STATES[value.lower()]

main.py

import argparse

from config import Config


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('-c', '--config', help='Custom config file.',
                        type=argparse.FileType('r'))
    args = parser.parse_args()

    Config.init_config(args.config)
    
    local_address = Config.get_or_else('smtp', 'BIND_ADDRESS', '127.0.0.1')
    port = Config.getint_or_else('smtp', 'PORT', 25)
    # ...
    
if __name__ == '__main__':
    main()