Spot the Bug

找出 bug

≈ 20 min · python-debugging · Open in WolfCode

Three broken functions. Each has exactly ONE bug. Find each with the smallest change that fixes it.

Bug #1 — off-by-one

Python · runnable

def greet_all(names):
    greetings = []
    for i in range(len(names) - 1):           # ← BUG
        greetings.append(f"Hello, {names[i]}!")
    return greetings

print(greet_all(["Ada", "Bob", "Cat"]))     # only 2 greetings — wrong

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Bug #2 — function does nothing

Python · runnable

def max_three(a, b, c):
    return c                                  # ← BUG: always returns c

print(max_three(1, 5, 3))   # 3 — should be 5

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Bug #3 — logic inverted

Python · runnable

def count_evens(numbers):
    count = 0
    for n in numbers:
        if n % 2 != 0:                        # ← BUG: counts ODDS
            count += 1
    return count

print(count_evens([1, 3, 5, 7]))   # 4 — should be 0

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