'Looks like you've solved it'

That's not a kata issue, use question. for is a loop, and indexOf is a loop-alike method, they're nested so your algorithm is O(n ^ 2), it won't work.

If you get that error, change your language version to 3.6.0
I can't select other version, but to some people, 3.4.3 is shown too.

This problem is more difficult than a kyu 5 problem

It is not.

Quesion answered by Chrono79 alredy. Closing.

Thanks Chrono79

Yes, avoid them.

I should avoid nested loops all together? This problem is more difficult than a kyu 5 problem. By the way, thanks for the reply.

It's a problem with your code:

JavaScript Completions 2496

Your code should be O(n)

Mark your post as having spoiler content next time.
Both functions are O(n ^ 2) filter and includes are loop-alike functions and they're nested in the first one, the second one have two nested for loops. Neither won't work. Your code should be faster O(n).

Could you post your code in a comment (with a spoiler tag)? I think there's a problem with your code. In fact, many people say their code works in IDE but it always turns out the code is simply wrong.

Apart from that, you can swap variables in Python like this: a, b = b, a.

You should be able to select Python 3.6 now. I don't know if that error has anything to do with Python version though.

Damn, so I just wasted my time on this kata? :(
I guess I'll have to rewrite some of the code...

See the python versions available for this kata, they're less than 3.6.