[Python-Dev] PEP 479 and asyncio (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Fri Nov 28 10:12:05 CET 2014

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()" 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

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