A proposal for "rebooted" Python asynchronous I/O support

I think you misunderstood what I was saying. To understand the fundamental problem in the CPython (and Jython) VM, just think about the difference between CPython and Stackless. You can't `yield from' inside a new function invocation because of the way call frames are implemented in CPython. Only the callee of a `yield from' statement can yield. But you can explicitly stack yield froms in a call chain. Kinda messy, but it's a fundamental limitation of CPython.

Coroutines in languages like Lua are implemented more like threads, so coroutine semantics aren't limited to a single callee invocation. In Lua, invocation C in A->B->C can yield, even though coroutine resumption began in A. In CPython, when resuming A only A can yield. A can, however, _explicitly_ invoke B as a coroutine. But B (perhaps a library call) can't hide the details. A needs to adorn it's call to B in order to get coroutine semantics. Again, not so in Lua or some other languages.