On Fri, Oct 13, 2017 at 4:29 PM, Paul Moore firstname.lastname@example.org wrote: [..]
Nick's other async refactoring example is different. If the two forms he showed don't behave identically in all contexts, then I'd consider that to be a major problem. Saying that "coroutines are special" just reads to me as "coroutines/async are sufficiently weird that I can't expect my normal patterns of reasoning to work with them". (Apologies if I'm conflating coroutines and async incorrectly - as a non-expert, they are essentially indistinguishable to me). I sincerely hope that isn't the message I should be getting - async is already more inaccessible than I'd like for the average user.
Nick's idea that coroutines can isolate context was actually explored before in PEP 550 v3, and then, rather quickly, it became apparent that it wouldn't work.
Steve's comments were about a specific example about generators, not coroutines. We can't special case __aenter__, we simply can not. __aenter__ can be a chain of coroutines -- its own separate call stack, we can't say that this whole call stack is behaving differently from all other code with respect to execution context.
At this time, we have so many conflicted examples and tangled discussions on these topics, that I myself just lost what everybody is implying by "this semantics isn't obvious to me". Which semantics? It's hard to tell.
At this point of time, there's just one place which describes one well defined semantics: PEP 550 latest version. Paul, if you have time/interest, please take a look at it, and say what's confusing there.