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Bug hunt: fix code you did not write

PremiumAdvanced25 min3 exercises

Most code you will ever fix was written by someone else, often a past version of you. It has no comments that say "the bug is here". This lesson is three programs that are broken on purpose, in ways that real programs break.

A process that works on all of them:

Some bugs crash with a traceback. The ones in this lesson do not: they run happily and give the wrong answer, which is why they survive. One of them is a classic Python trap that catches experienced programmers too. Read the example, then go hunting.

The rest of this lesson is Premium

Three broken Python programs to repair: an off-by-one loop, the shared default list, and a "find the biggest" that fails on negative numbers.

Module
Python Advanced: Read tracebacks, handle errors on purpose, build your own types, then hunt bugs in code you did not write.
Challenges
  • The countdown that stops early
  • The list that remembers
  • Nobody wins

First challenge: The countdown that stops early

count_down(3) should print 3, 2 and 1 on their own lines, then Go!. It prints one number too few. Fix the bug without adding a separate print(1).

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