[Python-ideas] async/await and synchronous code (and PEP492 ?)

[Guido van Rossum]

No, we can't, because the async/await are interpreted by the *compiler*,
while the presence of an event loop is a condition of the *runtime*.

On Tue, May 5, 2015 at 2:03 PM, Eric V. Smith <eric at trueblade.com> wrote:

> On 5/5/2015 2:48 PM, Guido van Rossum wrote:
> > Quick notes:
> > - I don't think it's really possible to write realistic async code
> > independently from an async framework.
> > - For synchronous code that wants to use some async code, the pattern is
> > simple:
> >     asyncio.get_event_loop().run_until_complete(some_async_call(args,
> etc))
> > - We can probably wrap this in a convenience helper function so you can
> > just write:
> >     asyncio.sync_wait(some_async_call(args, etc))
> > - Note that this will fail (and rightly so!) if called when the event
> > loop is already running.
>
> If we're going through all of the effort to elevate await and async def
> to syntax, then can't the interpreter also be aware if it's running an
> event loop? Then, if we are running an event loop, await becomes "yield
> from", using the event loop. But if we're not running an event loop,
> then await becomes a blocking wait, using some version of
> run_until_complete, whether really from asyncio or baked into the
> interpreter.
>
> This way, I can write my library code as being async, but it's still
> usable from non-async code (although it would need to be called with
> await, of course).
>
> I'll admit I haven't thought this all the way through, and I'm still
> reading through PEP 492. But if I can write my async code as if it were
> blocking using await, why can't it really be blocking, too?
>
> Eric.
>
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-- 
--Guido van Rossum (python.org/~guido)
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