Python argparse unrecognized arguments

Question

I am trying to use argparse to parse command line arguments. Here is my code:

#!/usr/bin/python
# -*- coding: UTF-8 -*-
import argparse

def create_parser():
    parser = argparse.ArgumentParser()
    parser.add_argument('--allow_ips', nargs='*')
    return parser

if __name__ == '__main__':
    parser = create_parser()
    namespace = parser.parse_args()

When the script is executed like this, argparse complains about unrecognized arguments.

./prog.py --allow_ips=192.168.0.10 192.168.0.11 192.168.0.12

But when the script is executed like this, argparse is satisfied.

./prog.py --allow_ips 192.168.0.10 192.168.0.11 192.168.0.12

How should I change my code so '=' can be used in the argument list?

Answer 1

According to the argparse documentation, passing * in the nargs argument means

All command-line arguments present are gathered into a list.

When you invoke your program without the equal sign, all three IP addresses are considered part of the --allow_ips argument; they will be available to your program in a list.

When you invoke your program with the equal sign, only the first IP address is considered part of the --allow_ips argument. argparse then tries to parse the second and third IP addresses. But it cannot because your program does not take any positional arguments. So argparse raises an exception.