Writing Clean Python Code, for Kids

This topic opens with a demonstration rather than an assertion: the exact same calculation, once written with meaningless single-letter variables and once with real names, produces the identical output both times. Python genuinely does not care what anything is called — the entire value of a good name is for the human reading the code afterward, and stating that plainly, rather than treating good naming as an unexplained style preference, is the point.

Magic numbers — bare literals with no stated meaning nearby — get the same treatment: not a warning to take on faith, but a demonstrated bug. The same threshold, typed as a bare number in two different places, quietly drifts out of sync when only one occurrence gets updated. A named constant makes that specific failure structurally impossible, since both checks then read the same name rather than two literals that merely happen to currently match.

The topic closes on two levels of duplication, taught as genuinely different skills: spotting identical repeated lines, and the harder task of recognising two functions that look different — different names, a different hardcoded number — but share the exact same underlying shape. Extracting that shared shape into one parameterised function is where the topic ends, with a combined refactor level whose only real test is behaviour preservation: the code must do exactly what it did before, and do it more clearly.