Simon Willison’s Weblog

Free Threaded Python With Asyncio. Jamie Chang expanded my free-threaded Python experiment from a few months ago to explore the interaction between Python's asyncio and the new GIL-free build of Python 3.13.

The results look really promising. Jamie says:

Generally when it comes to Asyncio, the discussion around it is always about the performance or lack there of. Whilst peroformance is certain important, the ability to reason about concurrency is the biggest benefit. [...]

Depending on your familiarity with AsyncIO, it might actually be the simplest way to start a thread.

This code for running a Python function in a thread really is very pleasant to look at:

result = await asyncio.to_thread(some_function, *args, **kwargs)

Jamie also demonstrates asyncio.TaskGroup, which makes it easy to execute a whole bunch of threads and wait for them all to finish:

async with TaskGroup() as tg:
    for _ in range(args.tasks):
        tg.create_task(to_thread(cpu_bound_task, args.size))