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On Thu, Oct 17, 2013 at 11:55 AM, Oscar Benjamin <oscar.j.benjamin@gmail.com> wrote:

On 17 October 2013 19:40, Xavier Morel <python-dev@masklinn.net> wrote:

> I think there's already a significant split between context managers

> which handle the lifecycle of a local resource (file, transaction) and

> those which purport to locally alter global-ish state (cwd,

> decimal.localcontext, logging.captureWarnings, redirect_stdout).

>

> And the latter worries me (much more than the very localized behavior of

> suppress) because I don't see any way to implement them safely and

> correctly when mixing it with coroutines in today's Python (some of them

> aren't even thread-safe), all of that while I expect coroutines will see

> significantly more use in the very near future with yield from and

> tulip's promotion of coroutine-style async.

I maybe misunderstanding how the �coroutine-style async works but I
would have thought that it would be as simple as: don't use
global-state-restoring-context-managers around statements that yield
control (it would be simpler if there was a good term for describing
that kind of CM). That's simpler to implement and computationally
cheaper than e.g. the thread-local state used by the decimal module.

Context managers that actually save and restore \*global\* state are already not thread-safe, so concluding they are also not coroutine-safe (or task-safe?) seems a small step.

I'd be more worried about context manager that use thread-local state -- there is no similar concept in Tulip.

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