Over the past years, two major players invested into the future of Python. Microsoft’s Faster CPython team is pushed ahead with impressive performance improvements for the CPython interpreter, which has gotten at least 2x faster since Python 3.9. They also have a baseline JIT compiler for CPython, too. At the same time, Meta is worked hard on making free-threaded Python a reality to bring classic shared-memory multithreading to Python, without being limited by the still standard Global Interpreter Lock, which prevents true parallelism.

Both projects deliver major improvements to Python, and the wider ecosystem. So, it’s all great, or is it?

In this talk, I’ll discuss some of the aspects the Python core developers and wider community seem to not regard with the same urgency as I would hope for. Concurrency makes me scared, and I strongly believe the Python ecosystem should be scared, too, or look forward to the 2030s being “Python’s Decade of Concurrency Bugs”. We’ll start out reviewing some of the changes in observable language semantics between Python 3.9 and today, discuss their implications, and because of course I have some old ideas lying around, try to propose a way fordward. In practice though, this isn’t a small well-defined research project. So, I hope I can inspire some of you to follow me down the rabbit hole of Python’s free-threaded future.