[Python-Dev] On suppress()'s trail blazing (was Re: cpython: Rename contextlib.ignored() to contextlib.ignore()) (original) (raw)

Guido van Rossum guido at python.org
Thu Oct 17 21:01:30 CEST 2013

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

wrote:

On 17 October 2013 19:40, Xavier Morel <python-dev at 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, redirectstdout). > > 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.

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