On Jan 10, 2018 07:17, "Yury Selivanov" <yselivanov...@gmail.com> wrote:
Wasn't PEP 555 rejected by Guido? What's the point of this post? I sure hope there is a point. I don't think mentioning PEP 555 in the discussions should hurt. A typo in my post btw: should be "PEP 567 (+568 ?)" in the second paragraph of course. -- Koos (mobile) Yury On Wed, Jan 10, 2018 at 4:08 AM Koos Zevenhoven <k7ho...@gmail.com> wrote: > Hi all, > > I feel like I should write some thoughts regarding the "context" > discussion, related to the various PEPs. > > I like PEP 567 (+ 567 ?) better than PEP 550. However, besides providing > cvar.set(), I'm not really sure about the gain compared to PEP 555 (which > could easily have e.g. a dict-like interface to the context). I'm still not > a big fan of "get"/"set" here, but the idea was indeed to provide those on > top of a PEP 555 type thing too. > > "Tokens" in PEP 567, seems to resemble assignment context managers in PEP > 555. However, they feel a bit messy to me, because they make it look like > one could just set a variable and then revert the change at any point in > time after that. > > PEP 555 is in fact a simplification of my previous sketch that had a > .set(..) in it, but was somewhat different from PEP 550. The idea was to > always explicitly define the scope of contextvar values. A context manager > / with statement determined the scope of .set(..) operations inside the > with statement: > > # Version A: > cvar.set(1) > with context_scope(): > cvar.set(2) > > assert cvar.get() == 2 > > assert cvar.get() == 1 > > Then I added the ability to define scopes for different variables > separately: > > # Version B > cvar1.set(1) > cvar2.set(2) > with context_scope(cvar1): > cvar1.set(11) > cvar2.set(22) > > assert cvar1.get() == 1 > assert cvar2.get() == 22 > > > However, in practice, most libraries would wrap __enter__, set and > __exit__ into another context manager. So maybe one might want to allow > something like > > # Version C: > assert cvar.get() == something > with context_scope(cvar, 2): > assert cvar.get() == 2 > > assert cvar.get() == something > > > But this then led to combining "__enter__" and ".set(..)" into > Assignment.__enter__ -- and "__exit__" into Assignment.__exit__ like this: > > # PEP 555 draft version: > assert cvar.value == something > with cvar.assign(1): > assert cvar.value == 1 > > assert cvar.value == something > > > Anyway, given the schedule, I'm not really sure about the best thing to do > here. In principle, something like in versions A, B and C above could be > done (I hope the proposal was roughly self-explanatory based on earlier > discussions). However, at this point, I'd probably need a lot of help to > make that happen for 3.7. > > -- Koos > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: https://mail.python.org/mailman/options/python-dev/ > yselivanov.ml%40gmail.com >
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