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

[Guido van Rossum]

Using an Event is slightly better because you just wait for it -- you don't
have to catch an exception. It's just not one of the better-known parts of
asyncio.

On Fri, Dec 18, 2015 at 1:42 PM, Andrew Barnert <abarnert at yahoo.com> wrote:

> On Friday, December 18, 2015 1:09 PM, Guido van Rossum <guido at python.org>
> wrote:
>
>
> >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).
>
> Yeah, that is a potential problem.
>
> The traditional C solution is to just allow passing -1 to mean "forever",*
> ideally with a constant so you can just say "sleep(FOREVER)". Which, in
> Python terms, would presumably mean "asyncio.sleep(asyncio.forever)", and
> it could be a unique object or an enum value or something instead of
> actually being -1.
>
> * Or at least "until this rolls over 31/32/63/64 bits", which is where you
> get those 49-day bugs from... but that wouldn't be an issue in Python
>
> > But I do feel it's not important enough to add a new function or method.
>
> Definitely agreed.
> >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.)
>
>
> OK, I thought the OP's code looked pretty clear as written: he wants to
> wait until cancelled, so he waits on something that pretty clearly won't
> ever finish until he's cancelled. If that (or an Event or whatever) is the
> best way to spell this, then I can't really think of any good uses for
> sleep(forever).
>



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