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

[Yury Selivanov]

Hi,

On 2015-04-23 3:30 AM, Wolfgang Langner wrote:
> Hi,
>
> most of the time I am a silent reader but in this discussion I must step in.
> I use twisted and async stuff a lot over years followed development of
> asyncio closely.
>
> First it is good to do differentiate async coroutines from generators. So
> everyone can see it and have this in mind
> and don't mix up booth. It is also easier to explain for new users.
> Sometimes generators blows their mind and it takes
> a while to get used to them. Async stuff is even harder.
>
> 1. I am fine with using something special instead of "yield" or "yield
> from" for this. C# "await" is ok.
>
> Everything else suggested complicates the language and makes it harder to
> read.
>
> 2.
> async def f(): is harder to read and something special also it breaks the
> symmetry in front (def indent).
> Also every existing tooling must be changed to support it. Same for def
> async, def f() async:
> I thing a decorator is enough here
> @coroutine
> def f():
> is the best solution to mark something as a coroutine.

You can't combine a keyword (await) with runtime decorator. Also
it's harder for tools to support @coroutine / @inlineCallbacks
than "async".
>
>
> 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.

I only lived without it because I used greenlets for async
for's & with's.  There must be a native language concept to
do these things.

> Same for with statement.
>
> The main use case suggested was for database stuff and this is also where
> most are best with
> defer something to a thread and keep it none async.
>
>
> All together it is very late in the development cycle for 3.5 to
> incorporate such a big change.

The PEP isn't a result of some quick brainstorming.  It's a
result of long experience using asyncio and working around
many painpoints of async programming.

> Best is to give all this some more time and defer it to 3.6 and some alpha
> releases to experiment with.

There is reference implementation.  asyncio is fully ported,
every package for asyncio should work.  You can experiment right now
and find a real issue why the PEP doesn't work.


Yury