[Python-Dev] Timeout for PEP 550 / Execution Context discussion

Yury Selivanov yselivanov.ml at gmail.com
Mon Oct 16 12:53:00 EDT 2017

On Mon, Oct 16, 2017 at 7:44 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> So going down this path would lock in the *default* semantics for the
> interaction between context variables and generators as being the same as
> the interaction between thread locals and generators, but would still leave
> the door open to subsequently introducing an opt-in API like the
> "contextvars.iter_in_context" idea for cases where folks decided they wanted
> to do something different (like capturing the context at the point where
> iterator was created and then temporarily switching back to that on each
> iteration).

I think we can still implement context isolation in generators in
later versions for ContextVars.  In 3.7, ContextVars will only support
async tasks and threads.  Using them in generators will be
*documented* as unsafe, as the context will "leak out".  Fixing
generators in some later version of Python will then be a feature/bug
fix.  I expect almost no backwards compatibility issue, same as I
wouldn't expect them if we switched decimal to PEP 550 in 3.7.


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