On Wed, Nov 8, 2017 at 9:31 AM, Chris Angelico <ros...@gmail.com> wrote: > On Thu, Nov 9, 2017 at 3:19 AM, Ian Kelly <ian.g.ke...@gmail.com> wrote: >> I was not referring to the possible future use of yield from for async >> generators; I was referring to the possibility *today* of using "yield >> from" as a synonym for *await*. As far as I know the only major >> obstacle to that is that the authors (with good reason) made it a >> SyntaxError. This is exactly the same sort of situation: it's a >> construct that would otherwise be perfectly valid, but it's made a >> SyntaxError specifically to prevent users from doing some the devs >> don't want them to. > > I don't understand why you would use "yield from" as a synonym for > "await". They are not equivalent. Why would you use one in place of > the other?
There's not really a good reason to use "yield from" with "async def" when you could just use "await", but the point is that in principle you could. In a generator-based coroutine (e.g. asyncio prior to Python 3.5), "yield from" is used to pause the coroutine and wait on some future. In a native coroutine (e.g. after Python 3.5), "await" is used to pause the coroutine and wait on some future. The implementation AIUI is essentially the same; the __await__ method is even required to return an iterator, just like __iter__. That's why I'm saying that they're basically synonyms. All that's really separating them is the syntax error. -- https://mail.python.org/mailman/listinfo/python-list
