[Python-Dev] async/await behavior on multiple calls

[Andrew Svetlov]

Both Yury's suggestions sounds reasonable.

On Tue, Dec 15, 2015 at 10:24 PM, Yury Selivanov
<yselivanov.ml at gmail.com> wrote:
> Hi Roy and Guido,
>
> On 2015-12-15 3:08 PM, Guido van Rossum wrote:
> [..]
>>
>>
>> I don't know how long you have been using async/await, but I wonder if
>> it's possible that you just haven't gotten used to the typical usage
>> patterns? In particular, your claim "anything that takes an `awaitable` has
>> to know that it wasn't already awaited" makes me sound that you're just
>> using it in an atypical way (perhaps because your model is based on other
>> languages). In typical asyncio code, one does not usually take an awaitable,
>> wait for it, and then return it -- one either awaits it and then extracts
>> the result, or one returns it without awaiting it.
>
>
> I agree.  Holding a return value just so that coroutine can return it again
> seems wrong to me.
>
> However, since coroutines are now a separate type (although they share a lot
> of code with generators internally), maybe we can change them to throw an
> error when they are awaited on more than one time?
>
> That should be better than letting them return `None`:
>
>     coro = coroutine()
>     await coro
>     await coro  # <- will raise RuntimeError
>
>
> I'd also add a check that the coroutine isn't being awaited by more than one
> coroutine simultaneously (another, completely different issue, more on which
> here: https://github.com/python/asyncio/issues/288).  This was fixed in
> asyncio in debug mode, but ideally, we should fix this in the interpreter
> core.
>
> Yury
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-- 
Thanks,
Andrew Svetlov