Online coding and Python classes in Corby

The learner downloads Ordnance Survey Code-Point Open, the free national postcode file, and keeps the 1,567 postcodes in the NN17 and NN18 districts: 909 and 658 of them. Every postcode is eight characters, such as NN17 1AA. A small wrapper counts each time Python compares two postcodes. The same list is then sorted from five starting orders, by Python's built-in sort and by a plain merge sort that splits the list in half every time.

On a list that is already in order, Python makes 1,566 comparisons, the minimum possible: it checks each neighbouring pair once, sees one long run and stops. A reversed list is spotted as a single descending run and flipped, so it costs the same. With only 15 pairs out of place, Python still needs fewer than half as many comparisons as merge sort. Once the order is random the advantage disappears and both need around 14,600 to 14,700, a little under the textbook n log2 n of about 16,600 for this list. Python's sort is called Timsort; since Python 3.11 it merges its runs using a refined rule known as Powersort.

Radix sort takes another route. It sorts by the last character first, dealing every postcode into a bucket for that character while keeping their order within each bucket, then repeats for each character moving left. Seven characters vary, so seven passes of 1,567 placements, 10,969 in all, give exactly the same result as sorted(), whatever the starting order, without a single comparison. The catch is that it needs keys of a fixed shape, which postcodes happen to have.

Measuring rather than guessing lets Corby teenagers judge AI-written code for themselves, a solid reason to learn Python in 2026. The longer argument is in why teenagers should still learn to code in 2026.