This main function implements the CLI

def main():
    """"This main function implements the CLI"""
    parser = argparse.ArgumentParser(description='Do something awesome')
    parser.add_argument('input_list', nargs='+',
                        type=str, default=sys.stdin)
    parser.add_argument('-o', '--outfile', nargs='?',
                        type=argparse.FileType('w'), default=sys.stdout)
    args = parser.parse_args()

    input_list = args.input_list
    print '\n'.join(get_ips_from_cidr_subnets(input_list))