An answer that may not exist in Python
Python interview exercise on Errors & Context Managers, difficulty 1 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
Write average(nums) that returns the mean as a float, or None for an empty list. Dividing by zero would raise ZeroDivisionError; decide before it happens.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Progress is saved in your browser, and in your account if you sign in.