[Python-Dev] PEP 380 (yield from a subgenerator) comments

[P.J. Eby]

At 10:56 AM 3/26/2009 +0000, Antoine Pitrou wrote:
>Guido van Rossum <guido <at> python.org> writes:
> >
> > That's stating it a little too strongly. Phillip has shown how with
> > judicious use of decorators and helper classes you can get a
> > reasonable approximation, and I think Twisted uses something like
> > this, so it's not just theory. I think the best you can do without new
> > syntax though is still pretty cumbersome and brittle, which is why I
> > have encouraged your PEP.
>
>It remains to be seen whether Twisted and other libraries (Kamaelia?) can
>benefit from this PEP.

They don't get any new features, and would require (possibly 
significant) changes in order to be able to take advantage of the syntax.

And they *still* wouldn't be able to do away with their trampolines 
-- the new trampolines would just be able to avoid the need for a 
generator stack, if they previously had one to begin with.  From your 
description, it sounds like Twisted's version of this doesn't even use a stack.

(Note: by "trampoline" I mean, "thing that processes yielded values 
and manages the resumption of the generator", which need not be 
global.  The example trampoline I posted earlier is also implemented 
as a decorator, and could be trivially extended via a lookup table to 
handle deferreds, delayed calls, or whatever else you wanted it to 
support as yield targets.)