TypeError: tuple cannot be changed

What this problem practises

Tuples are immutable containers that may themselves hold mutable objects, and it is the comma — not the parentheses — that builds one. Any unpacking where the counts disagree raises ValueError.

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: medium — expect to hold two interacting rules in your head at once, such as a boundary combined with a mutation.

The challenge

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Keep going

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