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Think of a bug that you met while working through this book, or write one on purpose.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Think of a bug that you met while working through this book, or write one on purpose. Write the five steps for it: how you reproduced it, where you located it, the explanation in one sentence, the one change that you made, and the test that you keep.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. There is no one right answer, so here is an example, to show the shape of a good one.
- Reproduce.
running_total([3, 1, 4, 1, 5])gave[3, 4, 8, 9]. A list of two items,[1, 2], gave[1]: the smallest failing input. - Locate. A
printofiinside the loop showed thatistopped one item early. - Explain. "The loop is
range(len(numbers) - 1), so the last item is never added." - Fix one thing. Change
len(numbers) - 1tolen(numbers). - Test again, and keep the test. The failing case passes. The old tests pass. The case
[1, 2]becomes a new test:assert running_total([1, 2]) == [1, 3].
Check. A good answer has all five steps, explains the cause before the fix, and ends with a test that stays.
Answer: Your own bug, in the five steps.
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