[Python-Dev] PEP 492: What is the real goal? (original) (raw)

Jim J. Jewett jimjjewett at gmail.com
Thu Apr 30 19:24:27 CEST 2015

On Wed, Apr 29, 2015 at 2:26 PM, Paul Moore <p.f.moore at gmail.com> wrote:

On 29 April 2015 at 18:43, Jim J. Jewett <jimjjewett at gmail.com> wrote:

So? PEP 492 never says what coroutines are in a way that explains why it matters that they are different from generators.

...

Looking at the Wikipedia article on coroutines, I see an example of how a producer/consumer process might be written with coroutines:

var q := new queue coroutine produce loop while q is not full create some new items add the items to q yield to consume coroutine consume loop while q is not empty remove some items from q use the items yield to produce (To start everything off, you'd just run "produce"). I can't even see how to relate that to PEP 429 syntax. I'm not allowed to use "yield", so should I use "await consume" in produce (and vice versa)?

I think so ... but the fact that nothing is actually coming via the await channel makes it awkward.

I also worry that it would end up with an infinite stack depth, unless the await were actually replaced with some sort of framework-specific scheduling primitive, or one of them were rewritten differently to ensure it returned to the other instead of calling it anew.

I suspect the real problem is that the PEP is really only concerned with a very specific subtype of coroutine, and these don't quite fit. (Though it could be done by somehow making them both await on the queue status, instead of on each other.)

-jJ

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