RecursionError: counting the wrong way

What this problem practises

Recursion needs a base case that actually triggers. A missing or drifting base case ends in RecursionError, and the call-stack order decides which value comes back first when predictions are made by eye.

This is a fix-the-bug problem: a short program is given in its broken state, and the task is to repair the code so it produces the required output. The interactive editor runs your fixed version in the browser and checks it for you — no setup, no local interpreter.

Difficulty: hard — the naive reading is wrong, and the answer depends on tracking state precisely through the snippet.

The challenge

This countdown has a base case but still crashes with RecursionError because it counts UP. Fix the step so it prints 3 down to 1, one per line.

The code runs in PyDebug’s in-browser compiler. Open the problem, run the snippet, watch the exact error or output, and keep iterating until it is right. Signed-in solves count toward XP and your daily streak.

The snippet

The interactive editor pre-fills exactly this code, broken and ready to repair:

def countdown(n):
    if n <= 0:
        return
    print(n)
    countdown(n + 1)
countdown(3)

More problems

• Factorial of 4 medium
• Factorial of 7 medium
• Set removes duplicates automatically easy

Keep going

• Python debugging guide — a systematic method for finding bugs like this one fast.
• Browse every recursion problem in this topic.
• Common Python errors and what they actually mean, plus the Python glossary for any term used on this page.