Correct, I was not using Numpy. I did not think of a good way to fit my program into a Numpy shaped solution. The main point is that I didn't NEED to try, as an almost literal translation to Julia worked much better. I also did not try using Numba, which I suspect would have given me similar results to Julia. I am a fan of Python overall, but sometimes you just need to choose a tool that gets the job done with the least mental effort expended on the tool. This was a one-time script that needed to be written, no maintenance was needed: I just needed an answer, and within a certain amount of time.