[Async-sig] coroutine function vs. function returning awaitable

[Guido van Rossum]

It looks like what you have in that library is something that's awaitable
but not a coroutine. That's totally fine. (Other examples exist, e.g.
Futures!)

On Thu, Nov 2, 2017 at 8:33 PM, Chris Jerdonek <chris.jerdonek at gmail.com>
wrote:

> I'm asking because a project I've been contributing to has this "bug"
> reported:
>
> https://github.com/aaugustin/websockets/issues/300
>
> So I'm trying to see if it needs to be fixed or if it can be left alone.
>
> More generally, this made me wonder if there are any advantages to
> ensuring that asyncio.iscoroutine() returns True for an object if the
> object is meant to be used like a coroutine object. (For example,
> perhaps this is what will give you the nice "coroutine object hasn't
> been awaited" warnings.)
>
> It looks like types.coroutine() might be the answer if there are
> advantages (but I haven't tried it):
> https://www.python.org/dev/peps/pep-0492/#types-coroutine
>
> --Chris
>
> On Thu, Nov 2, 2017 at 8:16 PM, Guido van Rossum <guido at python.org> wrote:
> > iscoroutine() is usually used to turn something into a Future. Is that
> what
> > you want? (TBH I'm not sure why you're asking all this.)
> >
> > On Thu, Nov 2, 2017 at 7:49 PM, Chris Jerdonek <chris.jerdonek at gmail.com
> >
> > wrote:
> >>
> >> Thanks. And how about making asyncio.iscoroutine() return True for the
> >> return value? It looks like asyncio calls that one in a half-dozen
> places or
> >> so.
> >>
> >> —Chris
> >>
> >> On Thu, Nov 2, 2017 at 7:15 PM Guido van Rossum <guido at python.org>
> wrote:
> >>>
> >>> Re (1), there are only two places where asyncio calls
> >>> `iscouroutinefunction()`, and in both cases it raises a TypeError to
> remind
> >>> the user that a coroutine/awaitable object is required. So, it doesn't
> >>> really offer much of an advantage and I wouldn't worry about it.
> >>>
> >>> On Thu, Nov 2, 2017 at 4:51 PM, Chris Jerdonek <
> chris.jerdonek at gmail.com>
> >>> wrote:
> >>>>
> >>>> Hi,
> >>>>
> >>>> I have a 2-part question:
> >>>>
> >>>> 1) Say you have a function that returns an awaitable (but not a
> >>>> coroutine object). Are there any advantages or disadvantages to
> >>>> replacing this with a function for which asyncio.iscoroutinefunction()
> >>>> returns True and asyncio.iscoroutine() returns True for the return
> >>>> value? An advantage might be, say, additional checks that asyncio
> >>>> performs.
> >>>>
> >>>> 2) If there are advantages, is there a straightforward way to
> >>>> construct such a replacement? In the case I have in mind (from an open
> >>>> source project), the "function" you'd be starting with is the class
> >>>> constructor for an async context manager that is also awaitable. So
> >>>> the class has both __aenter__ and __await__ methods.
> >>>>
> >>>> As an example naive attempt, the following _wouldn't_ work:
> >>>>
> >>>>     @asyncio.coroutine
> >>>>     def connect():
> >>>>         return AsyncConnectManager()
> >>>>
> >>>> The reason this doesn't work is that wrapping connect() in
> >>>> @asyncio.coroutine() means the return value is no longer an async
> >>>> context manager (it no longer has an __aenter__ method). You have to
> >>>> await to get the underlying async context manager.
> >>>>
> >>>> Thanks,
> >>>> --Chris
> >>>>
> >>>> _______________________________________________
> >>>> Async-sig mailing list
> >>>> Async-sig at python.org
> >>>> https://mail.python.org/mailman/listinfo/async-sig
> >>>> Code of Conduct: https://www.python.org/psf/codeofconduct/
> >>>
> >>>
> >>>
> >>>
> >>> --
> >>> --Guido van Rossum (python.org/~guido)
> >
> >
> >
> >
> > --
> > --Guido van Rossum (python.org/~guido)
>



-- 
--Guido van Rossum (python.org/~guido)
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