Online coding and Python classes in Kingswinford

The learner asks OpenStreetMap for every named road in a rectangle drawn around the census centres of the Kingswinford built-up area. The reply holds 1,767 named stretches of road carrying 810 different names, from Abbots Mews to Zaria Court. Names ending in Road are the most common with 147, then Close with 128 and Drive with 102. The list is kept in the order the names first turn up in the reply, which is neither sorted nor properly random, much like real data usually is.

Shell sort picks a gap, say 40, and sorts the names that are 40 apart from one another using the card-player's method. Then it picks a smaller gap and repeats, finishing with a gap of 1. By that last pass the list is nearly in order, so little work remains. The Python is about ten lines, and the gaps are just a list handed to the function. The learner wraps each name so that every "is this one before that one?" adds 1 to a counter.

Adding gaps cut the work from 169,625 comparisons to between 10,067 and 12,471, and which gaps mattered. Shell's own rule, halve each time, was the weakest of the three. Knuth's list, where each gap is three times the next plus one, saved about 15% on it. Ciura's list, found by experiment in 2001 and not by a formula, did slightly better again. The last column shows the price. Give a plain one-gap sort a list that is already in order and it checks each neighbour once, 809 comparisons, and stops. Shell sort cannot know that and still makes every pass, so it takes thousands.

For scale, Python's built-in sorted() used 6,799 comparisons on the same list, and no method based on comparing pairs can promise fewer than about 6,664 for 810 items. The counts are for this one list of names; the rectangle is a box around the town and takes in some roads beyond it.

For a Kingswinford teenager, being able to measure what a program does is the difference between using AI and being led by it, and that skill is learned by coding. The longer argument is in why coding is worth learning in 2026.