[Async-sig] Adding asyncio.run() function in Python 3.6

[Roy Williams]

Yury this looks great!  Thanks for suggesting this.

One of the big problems I've seen with the basic approachability  of
async/await in Python is the lack of interpreter support.  Now this makes
that a lot easier by having a one function you can use makes this a lot
easier (One of the main things I use `curio` for is simply being able to
`curio.run` an Awaitable in the interpreter without having to go through
the normal asyncio dance).  I would love to see if we could extend this
even further to making `await` "Just Work" in the interpreter.

Thanks,
Roy


On Wed, Nov 16, 2016 at 12:53 PM, Yury Selivanov <yselivanov at gmail.com>
wrote:

>
> > On Nov 16, 2016, at 3:35 PM, Nathaniel Smith <njs at pobox.com> wrote:
> >
> > What's the use case for the async generator version? Could the yield be
> replaced by 'await loop.shutting_down()’?
>
> Async generator version (inspired by contextlib.contextmanager decorator)
> is needed in cases where you want loop.run_forever.
>
> The PR originally proposed to add `asyncio.forever()` (which is the same
> idea as `loop.shutting_down()`), but nobody particularly liked it.
>
> A couple of thoughts/reasons:
>
> 1. Some pretty intrusive modifications are required to be made in the
> event loop to make it work.  That means all other event loops (including
> uvloop) will have to be modified to support it.  This is the most important
> reason.
>
> 2. `loop.shutting_down()` is a no go because it’s a method on the loop
> object.  We can discuss `asyncio.shutting_down`.  The whole point of this
> discussion is to get rid of the event loop.
>
> 3. `await forever()` and `await shutting_down()` have a naming issue -
> both look weird:
>
>   async def main():
>     srv = await asyncio.start_server(…)
>     try:
>        await asyncio.shutting_down()  # or await forever()
>     finally:
>        srv.close()
>        await srv.wait_closed()
>
> In the above example, what does the second ‘await’ do?  Will it be
> resolved when the loop is stopped with ‘loop.stop()’? Or when a
> KeyboardInterrupt occurs?  What will happen if you await on it in parallel
> from 10 different coroutines?  It’s just difficult to define a clear
> semantics of this coroutine.
>
> Using an asynchronous generator for this case is easier in terms of
> implementation and in terms of specifying the execution semantics.  And the
> approach of using generators for such things isn’t new - we have
> contextlib.contextmanager decorator which is quite popular.
>
> Yury
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