[ant6n]

I find that unexpected. Java has had string builder optimization for a long time, and CPython is much much faster in this respect. It's not always easy to use "".join when using a string, so you end up having to build a separate array of strings in some cases. And building arrays isn't always that fast either. And [].join doesn't exist, so summing arrays is always kinda slow.

Anyway, all that is to say: I really like PyPy, and we use it a lot, but those _unexpected_ crazy slowdowns are unfortunate.