I think this showcases the other issue I commented a few years ago [1].
Pyodide and Cloudflare don't use the real network stack for http requests (they patched the functions to use JS `fetch` underneath). They also patched Python's async event loop to use JS event loop.
This has a major downside: incompatibility issues. JS event loop is preemptive (async functions get called regardless of you calling await on them) while Python is lazy (async functions only execute when you await them).
In my belief, the network semantics should be preserved. When the behavior differs issues start arising.
> Pyodide and Cloudflare don't use the real network stack for http requests
Pyodide in browsers _can't_ use the real network stack because of fundamental security principles of browsers. With direct networking you could get around the CORS restrictions.
Thanks to Gyeongjae Choi's work, Pyodide in Node/Cloudflare can use direct sockets. See this section of the blog post: https://blog.cloudflare.com/python-workers-ga/#using-postgre...
> JS event loop is preemptive
I think the word you want is "eager". Preemptive usually refers to things like signal handlers: when the signal is received the handler "preempts" normal execution without waiting for an explicit yield point.
In any case, with the WebLoop, Python coroutines stay lazy. The fundamental primitive a Python event loop needs to implement is call_later() which maps fairly cleanly to `setTimeout()`.
The reason we want to use the JS event loop is that the JS event loop is where all the actual I/O events in a JavaScript runtime happen. If you create a second event loop and run it, it will block actual IO on the JS event loop. So making uvloop work would be pointless.