The point of codewars is to practice your problem solving and coding skills by doing the problem yourself, without having a library do the enitre thing for you. Yes you're 100% right that a better and more convenient solution exists, but you won't learn anything about the concept itself if you don't think hard and just google a function for it instead

And about banning the library, you're right that they could've banned it, but it wasn't intended to be used, otherwise the kata would be 7 or 8 kyu instead

Yeah

Am I correct in saying that this wouldn't work if there were opening parentheses without closing parentheses to match it?

Same for me. I ran it a few more times and eventually it passed.

Wow there's a lot of angry people in the comments. Seriously, this is how you code in python and we all know it. Why code something that already exists. If they didn't want the library, they could have made a test to ban it.