Lesson 6 — Spot the bug: the empty list

The case nobody asked about

AI answers usually work for the example in your prompt — and often break on the inputs nobody mentioned. The classic one is the empty list:

sum([]) / len([])   # ZeroDivisionError: division by zero
max([])             # ValueError

Before trusting a function, ask: what happens with nothing? An empty list, an empty string, zero, None.

Then decide what the function should do and write it down: here, the average of no scores is None ("no data"), not a crash and not 0 (which would look like a real score).

if not items:     # True for an empty list
    return 0      # or whatever "no answer" should be

Why it matters: real data is messy. A new user has no scores yet, and "crashes for new users" is a very bad first impression.