[Python-Dev] async/await in Python; v2 (original) (raw)

Wolfgang Langner tds333+pydev at gmail.com
Thu Apr 23 17:57:21 CEST 2015

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🔞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. transaction = yield from connection.transaction() try: ... except: yield from transaction.rollback() else: yield from transaction.commit() is certainly more irritating than async with connection.transcation(): ... I had also a need for async loop. But there are other solutions like channels, not needing a new syntax. Also possible a function returning futures and yield in the loop with a sentinel. All this goes the road down to a producer consumer pattern. Nothing more. I know I'm a bad guy to make such comments, too bad there's a bit of truth in them, or everyone would just call me an a%$&ole right away. Generally, I already provided feedback (on asyncio list) that asyncio is based not on native Python concepts like a coroutine, but on foreign concurrency concepts like callback or Future, and a coroutine is fitted as a second-class citizen on top of that. I understand why that was done - to not leave out all those twisteds from a shiny new world of asyncio, but sometimes one may wonder if having a clear cut would've helped (compat could then have been added as a clearly separate subpackage, implemented in terms of coroutines). Now people coming from non-coroutine frameworks who were promised compatibility see "bad" things in asyncio (and related areas), and people lured by a promise of native Python framework see bad things too. This has nothing to do with people using twisted or other async frameworks like tornado. I think a coroutine should be first class. But all this should be done in a way a beginner can handle and not design this stuff for experts only. I think that most of async frameworks out there are for experts only. Precisely because of 'yield from', 'yield', inlineCallbacks, '@coroutine', channels and other stuff. PEP 492 will make it all easier. And Twisted can use its features too.

Yes and it is good to make it easier. But not complicate it for others. Beginners will be confronted with all this new syntax an my feel lost. Oh I have to different for loops, one with async. Same for with statement.

If we do this we scare away new people.

It doesn't scare away anyone. async/await were the most awaited features in dart and javascript. One of the most popular features in c#.

I like it in C#. I like await for Python but I don't like async there and how to specify it. I still think a decorator is enough and no special for and with syntax.

async in JavaScript is for execution a whole script asynchronously used in the script tag. dart is for the google universe with less usage outside.

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