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lesson

Count the vowels

objective: AI code review · strings · easy

Task type: fix broken code

⚠ simulated AI-generated code

This code is framed as if an AI coding assistant wrote it, and has a realistic issue AI assistants actually produce — sometimes a real bug, sometimes code that runs fine but is more complicated or less idiomatic than it needs to be. It is not from a real model call. Read it like you'd review any AI suggestion — don't assume it's correct, or well-written, just because it looks polished.

An AI assistant wrote count_vowels(s) to count how many vowels are in a string, checking each character against an explicit list of vowels in a nested loop. It looks thorough — but that thoroughness is covering for something it never checks.

fix this code so it matches

count_vowels("hello") is 2. count_vowels("xyz") is 0. count_vowels("APPLE") is 2.

○Passes the visible tests
○Passes the hidden tests (edge cases)

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count_vowels.pyattempt 0

def count_vowels(s):    # Manually checks each character against every vowel.    count = 0    vowels = ["a", "e", "i", "o", "u"]    for char in s:        for v in vowels:            if char == v:                count += 1    return count

Count the vowels

objective: AI code review · strings · easy

Task type: fix broken code

⚠ simulated AI-generated code

fix this code so it matches

count_vowels("hello") is 2. count_vowels("xyz") is 0. count_vowels("APPLE") is 2.

○Passes the visible tests

○Passes the hidden tests (edge cases)

def count_vowels(s): # Manually checks each character against every vowel. count = 0 vowels = ["a", "e", "i", "o", "u"] for char in s: for v in vowels: if char == v: count += 1 return count