[Python-ideas] An async facade?

[Jonathan Slenders]

As removing "yield" changes the return value of a function. Nothing
different.

For me +1 for the "StopIteration" proposal. That's certainly better, and
more generic than what I said.

So, the difference is still that the "await" proposal makes the @async
decorator implicit. I'm still in favor of this because
in asynchronous code, you can have really many functions with this
decorator. And if someone forgets about that, getting a generator object
instead of a Future is quite different in semantics.

P.S. excuse me, Terry.



2012/12/21 Jasper St. Pierre <jstpierre at mecheye.net>

> Note that the "return b" is already being handled through the
> "StopIteration" proposal.
>
> I'm not a fan of the new syntax because it means that removing all the
> "await" keywords from a method changes the return value. Requiring the
> decorator means that this can cleanly be handled in all cases, even if the
> decorator implementation is a bit ugly.
>
> This means that all we have left is the "await" vs. "yield" vs. "yield
> from" discussion. I don't think the new valuable enough to warrant a new
> keyword.
>
>
>
> On Thu, Dec 20, 2012 at 5:52 PM, Jonathan Slenders <jonathan at slenders.be>wrote:
>
>> Hi All,
>>
>> This week I finished some Python syntax on a Pypy fork. It was an
>> experiment I was working on this week. We really needed a cleaner way of
>> writing asynchronous code. So, instead of using the yield keyword and an
>> @async decorator, we implemented the 'await' keyword, similar to c#.
>>
>> So, because I just now subscribed to python-ideas, I cannot reply
>> immediately to the following thread:
>>
>> An async facade? (was Re: [Python-Dev] Socket timeout and completion
>> based sockets)
>>
>>
>> Anyway, like c# does, I implemented the await keyword for Python, and
>> should say that I'm really confident of the usability of the result. Personally,
>> I think this is a very clean solution for Twisted's @defer.inlineCalbacks,
>> Tornado's @gen.engine, and similar functions in other async frameworks. We
>> use it right now in a commercial web environment, where third party users
>> should have to be able to write asynchronous code as easy as possible in a
>> web based IDE.
>>
>> https://bitbucket.org/jonathanslenders/pypy
>>
>> Two interpreter hooks were added: (both accept a callable as parameter.)
>>
>> >>>> sys.setawaithandler(wrapper)
>> >>>> sys.setawaitresultwrapper(result_wrapper)
>>
>>
>> The first will set the I/O scheduler  a functions for wrapping others
>> functions which contain 'await' instead of 'yield'. This wrapper function
>> will receive a generator as input. So, 'await' still acts like 'yield' for
>> the interpreter, but the result is automatically wrapped by this function,
>> if the await keyword was found.
>>
>> The second function will wrap the return result
>> of asynchronous functions. So, unlike normal generators with 'yield'
>> keywords, where 'await' has been used, we still can return a result. But
>> this result will be wrapped by this function, so that the generator in
>> the scheduler  will be able te recognize the returned result.
>>
>> This:
>>
>> @defer.inlineCallbacks
>> def async_function(deferred_param):
>>     a = yield deferred_param
>>     b = yield some_call(a)
>>     yield defer.returnValue(b)
>>
>>
>> will now become:
>>
>> def async_function(deferred_param):
>>     a = await deferred_param
>>     b = await some_call(a)
>>     return b
>>
>>
>> So, while still being explicit, it requires minimal syntax, and
>> allows distinguishing between when to 'wait' for an asynchronous task, and
>> when to pass the Future object around.
>>
>> I really have no idea whether this has been proposed before, I can only
>> say that we are using it and it works pretty well.
>>
>> Cheers,
>> Jonathan
>>
>>
>>
>> _______________________________________________
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>> Python-ideas at python.org
>> http://mail.python.org/mailman/listinfo/python-ideas
>>
>>
>
>
> --
>   Jasper
>
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