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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.
You're only asked to return True if n is a digit, which is what the solution does. Nowhere in the kata description does it say you have to use regex.
I would argue in any case that it's better practice to use built-ins for this instead of bringing in the overhead of the regex library where it's not required.
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