The first thing that stuck out to me like a sore thumb was the string-concatenation-in-a-loop. Though the author was aware of its consequences he only addressed it late in the article, optimizing relatively trivial stuff like variable lookups first. And then he did so in a rather strange way, instead of adding string fragments to a list and then join()ing them.

Not sure how fast that loop would be in Python compared to the implied loop&join but I sure would have liked to see them compared.