On 17 January 2018 at 11:27, Nathaniel Smith <n...@pobox.com> wrote:
> On Tue, Jan 16, 2018 at 2:44 PM, Yury Selivanov <yselivanov...@gmail.com>
> wrote:
>> 4. ContextVar.reset(token) now raises a ValueError if the token was
>> created in a different Context.
>
> A minor bit of polish: given that Token objects have to track the
> associated ContextVar anyway, I think it'd be cleaner if instead of
> doing:
>
> token = cvar.set(...)
> cvar.reset(token)
>
> we made the API be:
>
> token = cvar.set(...)
> token.reset()
As a counterpoint to this, consider the case where you're working with
*two* cvars:
token1 = cvar1.set(...)
token2 = cvar2.set(...)
...
cvar1.reset(token1)
...
cvar2.reset(token2)
At the point where the resets happen, you know exactly which cvar is
being reset, even if you don't know where the token was created.
With reset-on-the-token, you're entirely reliant on variable naming to
know which ContextVar is going to be affected:
token1 = cvar1.set(...)
token2 = cvar2.set(...)
...
token1.reset() # Resets cvar1
...
token2.reset() # Resets cvar2
If someone really does want an auto-reset API, it's also fairly easy
to build atop the more explicit one:
def set_cvar(cvar, value):
token = cvar.set(value)
return functools.partial(cvar.reset, token)
reset_cvar1 = set_cvar(cvar1, ...)
...
reset_cvar1()
Cheers,
Nick.
--
Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia
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