mergeconfig.py

from argparse import ArgumentParser
from configparser import ConfigParser
import pprint


def main():
    # Read file config
    fparser = ConfigParser()
    fparser.read('config.conf')
    config = {'some.key': 'some_value'}  # Hard-coded default
    for section in fparser.sections():
        for key, value in fparser[section].items():
            if value is not None:
                config[section + '.' + key] = value

    # Read command-line config
    parser = ArgumentParser()
    parser.add_argument('--some.key')
    parser.add_argument('--some.key2')
    parser.add_argument('--other.key')
    args = parser.parse_args()

    for key, value in args.__dict__.items():
        if not value is None:
            config[key] = value
    return config

if __name__ == '__main__':
    pprint.pprint(main())