[Python-Dev] Timeout for PEP 550 (original) (raw)

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

Yury Selivanov yselivanov.ml at gmail.com
Tue Oct 17 15:55:38 EDT 2017

On Tue, Oct 17, 2017 at 2:25 PM, Guido van Rossum <guido at python.org> wrote:

On Tue, Oct 17, 2017 at 8:54 AM, Yury Selivanov <yselivanov.ml at gmail.com> [..]

My way of thinking about this: "getexecutioncontext()" returns you a shallow copy of the current EC (at least conceptually). So making any modifications on it won't affect the current environment. The only way to actually apply the modified EC object to the environment will be its 'run(callable)' method.

I understand that you don't want to throw away the implementation work you've already done. But I find that the abstractions you've introduced are getting in the way of helping people understand what they can do with context variables, and I really want to go back to a model that is much closer to understanding how instance variables are just self.dict. (Even though there are possible complications due to slots and @property.)

I don't really care about the implementation work that has already been done, it's OK if I write it from scratch again.

I actually like what you did in https://github.com/gvanrossum/pep550/blob/master/simpler.py, it seems reasonable. The only thing that I'd change is to remove "set_ctx" from the public API and add "Context.run(callable)". This makes the API more flexible to potential future changes and amendments.

In short, I really don't think there's a need for context variables to be faster than instance variables.

Well, even our current idea about the API, doesn't really prohibit us from adding a cache to ContextVar.get(). That would be an implementation detail, right? Same as our latest optimization for creating bound methods (CALL_METHOD & LOAD_METHOD opcodes), which avoids creating bound method instances when it's OK not to.

Yury

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