[Python-Dev] async/await in Python; v2

[Andrew Svetlov]

On Thu, Apr 23, 2015 at 3:27 PM, Wolfgang Langner
<tds333+pydev at gmail.com> wrote:
>
>
> On Thu, Apr 23, 2015 at 12:35 PM, Paul Sokolovsky <pmiscml at gmail.com> wrote:
>>
>> Hello,
>>
>> On Thu, 23 Apr 2015 12:18:51 +0300
>> Andrew Svetlov <andrew.svetlov at gmail.com> wrote:
>>
>> []
>>
>> > > 3.
>> > > async with and async for
>> > > Bead idea, we clutter the language even more and it is one more
>> > > thing every newbie could do wrong.
>> > > for x in y:
>> > >   result = await f()
>> > > is enough, every 'async' framework lived without it over years.
>> >
>> > async for i in iterable:
>> >     pass
>> >
>> > is not equal for
>> >
>> > for fut in iterable:
>> >     i = yield from fut
>>
>> But people who used Twisted all their life don't know that! They just
>> know that "async for" is not needed and bad.
>>
>
> I don't think it is bad nor not needed, but the syntax is not beautiful and
> for the 90% not doing async stuff irritating and one more thing to learn
> and do right/wrong.
>
> I had also a need for async loop. But there are other solutions like
> channels,
> not needing a new syntax.
>
By `channels` do you mean something like `asyncio.Queue`? It requires
that producer and consumer should be separate tasks. Often it works
(with some performance penalty cost) but creating 2 tasks is not
always obvious way to solve problem.

> Also possible a function returning futures and yield in the loop with a
> sentinel.
A proposal looks like guess to avoid `for` loop and use `while` everywhere.

Just compare `while` loop:

it = iter(it)
while True:
    try:
        i = next(it)
        process(i)
    except StopIteration:
        break

with `for` alternative:

for i in it:
    process(i)


>
> All this goes the road down to a producer consumer pattern. Nothing more.
>
I think one of the most convenient consumer-producer pattern
implementation in Python is `for` loop and iterators concept. It's
sometimes too limited but works pretty well in 95% of use cases.

>



-- 
Thanks,
Andrew Svetlov