There is no test with empty string afaik in Python. Your current code works, did you try printing the input when you got that error to check which input made your code fail?

I guess you added something to ignore empty words, but it's your code which was creating them:

input = 'Quis custodiet ipsos custodes ?'
['Quis', 'custodiet', 'ipsos', 'custodes', ''] # your words list

A word can have a single letter and your code tries to access out of that range. Not a kata issue.

P.S.: that wasn't the problem, your problem was your code created empty words.

conversion to set takes some time and set() is called in every iteration.

It's O(n), that's plenty fast.

everything is interlinked with maths + - * / 😂😑

me too lmao, 1.5 pages of notebook paper with scribbled sequences on it

Yeah, turns out multiplying something by itself multiple times comes in handy. Middle school math is very useful in general.