[Python-ideas] async objects

[Nathaniel Smith]

On Thu, Oct 6, 2016 at 12:45 AM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> Nathaniel Smith wrote:
>>
>> It wasn't that we created these keywords to solve some
>> implementation problem and then inflicted them on users.
>
>
> I disagree -- looking at the history of how we
> ended up with async/await, it looks to me like
> this is exactly what *did* happen.
>
> First we had generators. Then 'yield from' was
> invented to (among other things) leverage them as
> a way of getting lightweight threads. Then 'await'
> was introduced as a nicer way to spell 'yield from'
> when using it for that purpose.
>
> Saying that 'await' is good for you because it
> makes the suspension points visible seems to me
> a rationalisation after the fact. It was something
> that emerged from the implementation, not a
> prior design requirement.

I wasn't trying to write a detailed account of the development, as
much as try to capture some essential features. Myth, not history :-).

In the final design, the one and only thing that distinguishes
async/await from gevent is that in the former the suspension points
are visible, and in the latter they aren't. I don't really believe
that it's an accident that people put a lot of effort into creating
async/await in this way at a time when gevent already existed and was
widely used in production, and we have historical documents like
Glyph's blog arguing for visible yield points as a motivation for
async/await, but... even if you think it *was* an accident, it hardly
matters at this point. The core distinguishing feature between
async/await and gevent is the visibility of suspension points, so it
might as well be the case that async/await is designed for exactly
those people who want visible suspension points.

(And I didn't say await or visible suspension points are necessarily
"good for you" -- obviously the implicit and explicit interleaving
approaches have trade-offs you'll have to judge for yourself. But
there are some people in some situations who want implicit
interleaving and async/await is there for them.)

-n

-- 
Nathaniel J. Smith -- https://vorpus.org