Reflections on 2 years of CPython’s JIT Compiler: The good, the bad, the ugly
5 July 2025
This blog post includes my honest opinions on the CPython JIT. What I think we did well, what I think we could have done better. I’ll also do some brief qualititative analysis.
I’ve been working on CPython’s JIT compiler since before the very start. I don’t know how long that is at this point … 2.5, maybe almost 3 years? Anyways, I’m primarily responsible for Python’s JIT compiler’s optimizer.
Note that at this point of time, the JIT is still experimental. This means it’s not ready for prime time yet: this blog post may go out of date fairly quickly!
Here’s a short summary:
The good:
I think we’re starting to build a community around the JIT, which is great. The JIT is also teachable. We have newcomers coming in and contributing.
Could use improvement:
Performance Inaccurate coverage of the JIT
... continue reading