[Python-Dev] PEP 492: async/await in Python; v3

[Yury Selivanov]

Greg,

On 2015-04-29 5:13 AM, Greg Ewing wrote:
> Yury Selivanov wrote:
>>
>> On 2015-04-28 11:59 PM, Greg wrote:
>>
>>> On 29/04/2015 9:49 a.m., Guido van Rossum wrote:
>>>
>>>>     *But* every generator-based coroutine *must* be
>>>>     decorated with `asyncio.coroutine()`.  This is
>>>>     potentially a backwards incompatible change.
>>>>
>>>> See below. I worry about backward compatibility. A lot. Are you saying
>>>> that asycio-based code that doesn't use @coroutine will break in 3.5?
>>>
>>> That seems unavoidable if the goal is for 'await' to only
>>> work on generators that are intended to implement coroutines,
>>
>> Not sure what you mean by "unavoidable".
>
> Guido is worried about existing asyncio-based code that
> doesn't always decorate its generators with @coroutine.
>
> If I understand correctly, if you have
>
>    @coroutine
>    def coro1():
>       yield from coro2()
>
>    def coro2():
>       yield from ...
>
> then coro1() would no longer work. In other words,
> some currently legitimate asyncio-based code will break
> under PEP 492 even if it doesn't use any PEP 492 features.
>
> What you seem to be trying to do here is catch the
> mistake of using a non-coroutine iterator as if it
> were a coroutine. By "unavoidable" I mean I can't see
> a way to achieve that in all possible permutations
> without giving up some backward compatibility.

Please see my reply to Guido in other thread.

Yury