[Python-Dev] PEP 492: async/await in Python; version 5

[Paul Moore]

On 5 May 2015 at 22:38, Yury Selivanov <yselivanov.ml at gmail.com> wrote:
> n 2015-05-05 5:01 PM, Paul Moore wrote:
>>
>> On 5 May 2015 at 21:00, Yury Selivanov <yselivanov.ml at gmail.com> wrote:
>>>
>>> On 2015-05-05 3:40 PM, Jim J. Jewett wrote:
>>>>
>>>> On Tue May 5 18:29:44 CEST 2015, Yury Selivanov posted an updated
>>>> PEP492.
>>>>
>>>> Where are the following over-simplifications wrong?
>>>>
>>>> (1)  The PEP is intended for use (almost exclusively) with
>>>> asychronous IO and a scheduler such as the asynchio event loop.
>>>
>>> Yes. You can also use it for UI loops.  Basically, anything
>>> that can call your code asynchronously.
>>
>> Given that the stdlib doesn't provide an example of such a UI loop,
>> what would a 3rd party module need to implement to provide such a
>> thing? Can any of the non-IO related parts of asyncio be reused for
>> the purpose, or must the 3rd party module implement everything from
>> scratch?
>
> The idea is that you integrate processing of UI events to
> your event loop of choice.  For instance, Twisted has
> integration for QT and other libraries [1].  This way you
> can easily combine async network (or OS) calls with your
> UI logic to avoid "callback hell".

We seem to be talking at cross purposes. You say the PEP is *not*
exclusively intended for use with asyncio. You mention UI loops, but
when asked how to implement such a loop, you say that I integrate UI
events into my event loop of choice. But what options do I have for
"my event loop of choice"? Please provide a concrete example that
isn't asyncio. Can I use PEP 492 with Twisted (I doubt it, as Twisted
doesn't use yield from, which is Python 3.x only)? I contend that
there *is* no concrete example that currently exists, so I'm asking
what I'd need to do to write one. You pointed at qamash, but that
seems to be subclassing asyncio, so isn't "something that isn't
asyncio".

Note that I don't have a problem with there being no existing
implementation other than asyncio. I'd just like it if we could be
clear over exactly what we mean when we say "the PEP is not tied to
asyncio". It feels like the truth currently is "you can write your own
async framework that uses the new features introduced by the PEP". I
fully expect that *if* there's a need for async frameworks that aren't
fundamentally IO multiplexors, then it'll get easier to write them
over time (the main problem right now is a lack of good tutorial
examples of how to do so). But at the moment, asyncio seems to be the
only game in town (and I can imagine that it'll always be the main IO
multiplexor, unless existing frameworks like Twisted choose to compete
rather than integrate).

Paul