In my opinion, you should be free to look that up: that's what you'd do on the job as well. I also google it every time I need to use arg parsing in literally any language because I need it fairly infrequently, and frankly that's how this code came to be: too lazy to look it up again, too easy to write myself, and enjoying the writing of code. Any other solution would also be fine, this test would be about seeing if you can read and write code rather than if you come up with the (what the interviewers think) is the perfect solution.