Actually, now that I think of it, there’s no reason you need to join the 2 names into a single str. You could just leave it as a tuple of last, first and Python will know what to do in comparing them.

>>> sorted(student_ids, key = lambda i: ((rec := student_recs[i])['last'], rec['first']))
[632453, 1261456, 532153]

So the lambda would be returning ('Potter', 'Harry') rather than 'Potter, Harry'. But whatever. The := part is still the same.