On Wed, Nov 8, 2017 at 11:12 AM, Chris Angelico <ros...@gmail.com> wrote: > On Thu, Nov 9, 2017 at 5:05 AM, Ian Kelly <ian.g.ke...@gmail.com> wrote: >> 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. > > Except that "yield from" is used by generators to delegate to other > generators, and "await" is used by coroutines to delegate to other > coroutines. In an asynchronous generator, "yield" produces values, and > "yield from" would delegate to another asynchronous generator. They > are NOT synonyms.
Only because the devs have chosen to reserve the possibility of asynchronous generators. Abstractly, coroutines and generators are distinct concepts, but pragmatically, coroutines *are* generators. Native coroutines don't actually change this; they just do a better job of hiding it. -- https://mail.python.org/mailman/listinfo/python-list
