[Python-Dev] Simple coroutines?

[Phillip J. Eby]

At 01:16 PM 8/25/04 -0400, Clark C. Evans wrote:
>On Wed, Aug 25, 2004 at 12:13:46PM -0400, Phillip J. Eby wrote:
>| At 02:51 PM 8/25/04 +1200, Greg Ewing wrote:
>| >> If you could throw a special kind of exception (or even a regular
>| >> exception), and call traceback.resume() to pick up execution at the
>| >> point where it was thrown, whether thrown by a generator or a
>| >> regular function.
>| >
>| >Actually, it probably wouldn't be too hard to make exceptions
>| >resumable -- provided all the frames in between are Python. If the
>| >exception gets thrown through any C calls, though, resumption becomes
>| >impossible.  Some other structure is needed to hold the state of a
>| >resumable C call.
>|
>| Unfortunately, as was discussed on the previous Stackless thread, nearly
>| *all* Python bytecodes pass through C on their way to other Python code.
>
>However, the C code in the distribution could be scrubbed to make sure
>that it works with the mechanism.  And the C API could be detailed so
>that this case is managable; else, it is an "uncaught" exception.

Quick question: does Stackless' "greenlet" extension module do what you 
need?  I just built it and played around with it a bit.  One of the demos 
is a pseudo-generator implementation using a 'Yield' function that uses 
greenlet task switching to simulate the behavior of a normal generator 
function.

It looks to me that your "yield Cooperate" scenarios could perhaps be met 
by simply switching to a reactor/mainloop greenlet, when it's necessary to 
wait for an event, and by having your event callback switch back to the 
task's greenlet, returning a result if needed.

Interestingly, this greenlet thing looks like it would be perfect for 
peak.events, allowing me to get rid of all the generators and yield/resume 
stuff.  (In fairness, Bob Ippolito told me that before I ever implemented 
peak.events, but at the time greenlets didn't exist as an extension module 
that could be built outside of Stackless.)