[Python-Dev] PEP 479 and asyncio

[Greg Ewing]

Guido van Rossum wrote:

> The issue here is that asyncio only interprets StopIteration as 
> returning from the generator (with a possible value), while a Trollius 
> coroutine must use "raise Return(<value>)" to specify a return value; 
> this works as long as Return is a subclass of StopIteration, but PEP 479 
> will break this by replacing the StopIteration with RuntimeError.

I don't understand. If I'm interpreting PEP 479 correctly, in
'x = yield from foo', a StopIteration raised by foo.__next__()
doesn't get turned into a RuntimeError; rather it just stops the
sub-iteration as usual and its value attribute gets assigned to x.

As long as a Trollius coroutine behaves like something implementing
the iterator protocol, it should continue to work fine with
Return as a subclass of StopIteration.

Or is there something non-obvious about Trollius that I'm
missing?

-- 
Greg