It's not too hard actually. A line of python is roughly 80x slower than a line of C (no exaggeration). But a typical line of python does a lot more than a typical line of C. So things you can do with a "loose" loop (like once per 64k block) is usually ok in python. Things you have to do with a "tight" loop (like once per byte) need to be in C.

I once did a presentation about python performance optimization lessons from bup: http://lanyrd.com/2011/pycodeconf/sghxk/

And it's true, I'm not the most active maintainer anymore. The people who took over seem to be doing a pretty good job though.

I'd be curious to know if your stance on PyPy has changed at all since 2011 (if indeed it's something that you've taken any new long looks at since) given their progress in that time.

I know that I would humbly submit at the least that my position has moved to believing that PyPy is a viable option for high-speed code (albeit in substantial part due to better interaction with C, nowadays).

Not the author either, but I've made that decision based on profiling the code. It's generally easy to see which functions are slowing down performance and can be refactored to a more performant language.

The author is https://news.ycombinator.com/user?id=apenwarr, though it looks like he isn't the most active maintainer nowadays.