Input can be modified in python, and perhaps ruby.

Nope, not intended.

Closing this issue, and raising issue with exact information.

Same fail to my solution

Yep that was the issue. Is this intended? I've never run into an issue like this before.

You're modifying the list.

on python my tests all work but when i try attempt it shows that the expected answer for every random test is an empty list. this happens when i return any value. but if i return an empty list i get a full list instead as it should be.