At 08:21 PM 7/24/2010 -0700, Guido van Rossum wrote:

FWIW, the thing that was harder to debug when I tried to write some code involving generators and a trampoline recently, was thinking of a function as a generator without actually putting a yield in it (because a particular version of a coroutine pattern didn't need to block at all). Monocle uses a decorator to flag all coroutines which fixes this up in the right way, which I think is clever, but I'm torn about the need to flag every coroutine with a decorator -- Monocle makes the decorator really short (@_o) because, as Raymond (not Monocle's author but its advocate at EuroPython) said, "you'll be using this hundreds of times". Which I find disturbing in itself.

I haven't used Monocle, but in all the libraries I've written myself for this sort of thing (Trellis and peak.events), a decorator is only required for a generator that is a "root" task; everything else is just a normal generator. For example, in Trellis you use @Task.factory to mark a function as spawning an independent task each time it's called, but subgenerator functions called within the task don't need to be marked, and in fact the "yield from" is just a "yield" - the trampoline expects all yields of generators to be subgenerator calls. (PEP 380 can't do this of course, since it also doubles as a sort of 'yield *' - i.e., you may care about the yielded values) Note, though, that even in the sketch I just gave, you don't *really* need to decorate every function, just the ones that need to be called from *non*-decorated functions... i.e. "root" coroutines. Even then, you could *still* skip the decorator and replace: an_iter = decorated_root_function() with: an_iter = From(undecorated_root_function()) and not need to decorate *anything*.