[Python-ideas] Async API

Paul Colomiets paul at colomiets.name
Thu Oct 25 09:55:44 CEST 2012

Hi Guido,

On Thu, Oct 25, 2012 at 2:43 AM, Guido van Rossum <guido at python.org> wrote:
> On Wed, Oct 24, 2012 at 4:26 PM, Yury Selivanov <yselivanov.ml at gmail.com> wrote:
>> On 2012-10-24, at 7:12 PM, Guido van Rossum <guido at python.org> wrote:
>>> Ok, I can understand. But still, this is a problem with timeouts in
>>> general, not just with timeouts in a yield-based environment. How does
>>> e.g. Twisted deal with this?
>> I don't know, I hope someone with an expertise in Twisted can tell us.
>> But I would imagine that they don't have this particular problem, as it
>> should be related only to coroutines and schedulers that run them.  I.e.
>> it's a problem when you run some code and may interrupt it.  And you can't
>> interrupt a plain python code that uses callbacks without yields and
>> greenlets.
> Well, but in the Twisted world, if a cleanup callback requires more
> blocking calls, it has to spawn more deferred callbacks. So I think
> they *do* have the problem, unless they don't have a way at all to
> constrain the total running time of an action involving cascading
> callbacks. Also, they have inlineCallbacks which does use yield.

AFAIR, in twisted there is no timeout on coroutine, there is a timeout
on request, which is usually just a socket timeout. So there is no
problem of interrupting the code in arbitrary places.

Another twisted thing, is doing all writes asynchronously with respect
to user code, so if you want to write something and close a connection
for finalization you just call:


And they do not return deferreds, so it returns immediately even if
the socket is not writable at the moment. (IIRC, it never writes right
now, but rather from reactor callback)


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