On Fri, Oct 13, 2017 at 3:25 AM, Nick Coghlan email@example.com wrote: [..]
However, considering that coroutines are almost always instantiated at the point where they're awaited, I do concede that creation time context capture would likely also work out OK for the coroutine case, which would leave contextlib.contextmanager as the only special case (and it would turn off both creation-time context capture and context isolation).
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.