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

[Yury Selivanov]

Wolfgang,

On 2015-04-23 12:58 PM, Wolfgang Langner wrote:
> On Thu, Apr 23, 2015 at 6:22 PM, Yury Selivanov <yselivanov.ml at gmail.com>
> wrote:
>
>> Wolfgang,
>>
>>
>> On 2015-04-23 12:12 PM, Wolfgang Langner wrote:
>>
>>> On Thu, Apr 23, 2015 at 5:32 PM, Yury Selivanov <yselivanov.ml at gmail.com>
>>> wrote:
>>>
>>>   Hi Wolfgang,
>>>> On 2015-04-23 8:27 AM, Wolfgang Langner 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.
>>>>>
>>>>>   There is no way to do things wrong in PEP 492.  An object
>>>> either has __aiter__ or it will be rejected by async for.
>>>> An object either has __aenter__ or it will be rejected by
>>>> async with.
>>>>
>>>>   Don't mean it can be done wrong on execution or syntax level.
>>> I mean for a beginner it is not as easy an more and some will try
>>> async in some places, yes they will get an error. But there is a
>>> new possibility to get such errors if async is there for with and for
>>> statements.
>>> And the next beginner will then implement __aiter__ instead of __iter__
>>> because
>>> he/she don't get it.
>>>
>> Sorry, Wolfgang, but I don't get your argument.  Beginners
>> shouldn't just randomly try to use statements.  There is a
>> documentation for that.  Plus we can make exception messages
>> better.
>>
> Had to coach a lot of new users to Python and some to async stuff in
> twisted.
> And what beginners not should do don't care them. ;-)
> They will do strange stuff and go other way's than you expected. I only
> like to make
> it as easy as possible for them. Nothing more.
> Less keywords, less ways to do something, best only one way to do it.
>
>
>
> Don't get me wrong, I like the PEP it is well written and covers a lot of
> areas about async programming.
> I know Python must improve in this area and has a lot of potential.
> But don't hesitate, give the people time to try it and mature it. If all
> this should be in 3.5 it is to early.

The thing about this PEP is that it's build on existing
concepts that were validated with asyncio.

As for is it enough time to review it or not -- it's up to
BDFL to decide.  I'm doing my best trying to get the reference
implementation reviewed and to address all questions in the
PEP, hoping that it will help.

I can only say that if it doesn't land in 3.5, we'll have
to wait another *1.5 years*.  And it's not that people will
download CPython 3.6.alpha0 and start rewriting their code
and playing with it.  In the meanwhile, people want more
good reasons to migrate to Python 3, and I strongly believe
that this PEP is a great reason.

Moreover, it's several months before 3.5 is released. We still
will be able to slightly alter the behaviour and gather
feedback during beta periods.

>
> Also we can avoid the async keyword completely and do the same as for
> generators.
> If there is an await, it is a coroutine.
Unfortunately there is a problem with this approach:
refactoring of code becomes much harder.  That's one of the
corner cases that @coroutine decorator solves; see
https://www.python.org/dev/peps/pep-0492/#importance-of-async-keyword

Thanks,
Yury