The input validation is worthless; it should be removed or actually tested in random tests.

This doesn't make much sense with python.

Very simple and basic, not challenging at all.
Most languages already have built-in functions to check if a variable is an integer, so you should consider disabling them to make it more challenging.

Needs random tests

1. This Kata does not teach anything useful, nor does it present a fun challenge, as the user can simply aliase a built-in function to pass this Kata
2. Glaring lack of code coverage (i.e. test cases). Only 2 fixed assertions, no random assertions, etc. Pathetic.
3. PHP function naming convention is snake_case. Although I see why you avoided snake_case; the built-in function for this exact purpose is the name of the user-defined function in snake_case.

I suggest you unpublishing this Kata and coming up with something much better than this.

Why did you put mathematics in the 'Tags'? It should be with basic language function or similar tag. Or if you want to theach how to check it without built in functions than mention it in the description of the kata, or provide some resources for beginners to check possible ways to solve it. Otherwise nice kata! Keep up adding ;)