On 13Oct2017 1132, Yury Selivanov wrote:
On Fri, Oct 13, 2017 at 1:45 PM, Ethan Furman firstname.lastname@example.org wrote:
On 10/13/2017 09:48 AM, Steve Dower wrote: >
On 13Oct2017 0941, Yury Selivanov wrote:
Actually, capturing context at the moment of coroutine creation (in PEP 550 v1 semantics) will not work at all. Async context managers will break.
class AC: async def __aenter__(self): pass
^ If the context is captured when coroutines are instantiated, __aenter__ won't be able to set context variables and thus affect the code it wraps. That's why coroutines shouldn't capture context when created, nor they should isolate context. It's a job of async Task.
Then make __aenter__/__aexit__ when called by "async with" an exception to the normal semantics?
It seems simpler to have one specially named and specially called function be special, rather than make the semantics more complicated for all functions.
It's not possible to special case __aenter__ and __aexit__ reliably (supporting wrappers, decorators, and possible side effects).
Why not? Can you not add a decorator that sets a flag on the code object that means "do not create a new context when called", and then it doesn't matter where the call comes from - these functions will always read and write to the caller's context. That seems generally useful anyway, and then you just say that __aenter__ and __aexit__ are special and always have that flag set.
I still don't understand what Steve means by "more usable", to be honest.
I don't know that I said "more usable", but it would certainly be easier to explain. The Zen has something to say about that...