An example of how to use a config file which is overridden by command line arguments in Python.

config_file_and_command_line_arguments.py

#!/usr/bin/env python

import ConfigParser
import argparse
import logging
import os

def type_loglevel(level):
    try:
        result = getattr(logging, level.upper())
    except AttributeError:
        raise argparse.ArgumentTypeError("'%s' is not a valid log level. Please use %s" %
                                         (level, 
                                          [x for x in logging._levelNames.keys() 
                                           if isinstance(x, str)]))
    return result

if __name__=='__main__':
    conf_parser = argparse.ArgumentParser(
        # Turn off help, so we print all options in response to -h
            add_help=False
            )
    conf_parser.add_argument("-c", "--config",
                             help="Specify a configuration file", 
                             metavar="FILE")
    args, remaining_argv = conf_parser.parse_known_args()
    defaults = {
        "foo" : "default foo value",
        "bar" : "default bar value",
        "baz" : "default baz value",
        "loglevel" : "INFO"
        }
    if args.config:
        config = ConfigParser.SafeConfigParser(defaults)
        config.read([args.config])
        defaults = dict(config.items("Defaults"))
    
    for key in defaults.keys():
        if "\n" in defaults[key]:
             defaults[key] = [x.strip() for x in defaults[key].splitlines()]

    # Don't suppress add_help here so it will handle -h
    parser = argparse.ArgumentParser(
        # Inherit options from config_parser
        parents=[conf_parser],
        # print script description with -h/--help
        description=__doc__,
        # Don't mess with format of description
        formatter_class=argparse.RawDescriptionHelpFormatter,
        )
    parser.set_defaults(**defaults)
    parser.add_argument('-f', '--foo', 
                       help="Foo")
    parser.add_argument('-b', '--bar', 
                       help="Bar")
    parser.add_argument('-z', '--baz', 
                       help="Baz")
    parser.add_argument('-l', '--loglevel', type=type_loglevel,
                   help='Log level verbosity')
    args = parser.parse_args(remaining_argv)
    logging.basicConfig(level=args.loglevel)

    print args