[Python-Dev] Asynchronous context manager in a typical network server

[Guido van Rossum]

On Fri, Dec 18, 2015 at 12:45 PM, Andrew Barnert <abarnert at yahoo.com> wrote:

> On Dec 18, 2015, at 10:36, Guido van Rossum <guido at python.org> wrote:
>
> On Fri, Dec 18, 2015 at 10:25 AM, Szieberth Ádám <sziebadam at gmail.com>
> wrote:
>
>> Thanks for your reply Guido!
>>
>> > - In theory, instead of waiting for a Future that is cancelled by a
>> > handler, you should be able to use asyncio.sleep() with a very large
>> number
>> > (e.g. a million seconds).
>>
>> I was thinking on this too but it seemed less explicit to me than
>> awaiting a
>> pure Future with a short comment. Moreover, even millions of seconds can
>> pass.
>>
>
> 11 years.
>
>
> It's 11 days. Which is pretty reasonable server uptime.
>

Oops, blame the repr() of datetime.timedelta. I'm sorry I so rashly thought
I could do better than the OP.


> And probably just outside the longest test you're ever going to run. I
> don't trust myself to pick "a big number" when the numbers get this big.
> But I still sometimes sneak one past myself somehow. Hence my suggestion
> for a way to actually say "forever".
>

I guess we could make the default arg to sleep() 1e9. Or make it None and
special-case it. I don't feel strongly about this -- I'm not sure how
baffling it would be to accidentally leave out the delay and find your code
sleeps forever rather than raising an error (since if you don't expect the
infinite default you may not expect this kind of behavior). But I do feel
it's not important enough to add a new function or method.

However, I don't think "forever" and "until cancelled" are really the same
thing. "Forever" can only be interrupted by loop.stop(); "until cancelled"
requires indicating how to cancel it, and there the OP's approach is about
the best you can do. (Or you could use the Event class, but that's really
just a wrapper on top of a Future made to look more like threading.Event in
its API.)

-- 
--Guido van Rossum (python.org/~guido)
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