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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
But what numbers do you test in your local Python interpreter? Do you test the same numbers as Codewars does? Did you test
is_square(-1)
(which you can see in the error message)?Anyway, it is a question, not an issue (yet).
Are you testing it there with that input value?