Python: missing

from solution import alphanumeric
import codewars_test as test

in the sample tests and full tests

there is actually an issue here. since Codewars moved away from concatenating the user's solution and the tests for Python, whatever renaming and imports the user makes should stay contained within the solution module. however, because the Python tests suite does not explicitely import the user's function in this kata, Codewars inserts from solution import * to the tests for backwards-compatibility. alphanumeric should be imported explicitely instead; raising an issue about that

the reason your code fails is because you overwrite str in your import line

this means str is no longer what it should be in the Python code,
and so that breaks the tester

this is why you should never overwrite a built-in function, a module name, or a keyword, et cetera

first, you should use a spoiler flag if you post code

I added the flag to your comment