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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.
str shouldn't be used as a parameter in python, change it to s or string
The random tests in python are always expecting -1, no matter what the correct answer is.
Missing ':' at the end of function def
don't use "str" as the name of the parameter in python
More test cases. Also, unless you want this to be an easy kata then the list of list should have an unknown depth, to make it more interesting.