On Sun, Nov 12, 2017 at 7:27 AM, Guido van Rossum <gu...@python.org> wrote: > On Sun, Nov 12, 2017 at 2:53 AM, Chris Jerdonek <chris.jerdo...@gmail.com> > wrote: >> >> By the way, since we're already on the subject of asyncio tasks and >> (truncated) stack traces, this looks like a good opportunity to ask a >> question that's been on my mind for a while: >> >> There's a mysterious note at the end of the documentation of >> asyncio.Task's get_stack() method, where it says-- >> >> > For reasons beyond our control, only one stack frame is returned for a >> > suspended coroutine. >> >> (https://docs.python.org/3/library/asyncio-task.html#asyncio.Task.get_stack >> ) >> >> What does the "For reasons beyond our control" mean? What is it that >> can possibly be beyond the control of Python? > > > It's an odd phrasing, but it refers to the fact that a suspended generator > frame (which is what a coroutine really is) does not have a "back link" to > the frame that called it. Whenever a generator yields (or a coroutine > awaits) its frame is disconnected from the current call stack, control is > passed to the top frame left on that stack, and the single generator frame > is just held on to by the generator object. When you call next() on that, it > will be pushed on top of whatever is the current stack (i.e. whatever calls > next()), which *may* be a completely different stack configuration than when > it was suspended.
It is possible to get the await/yield from stack though, even when a generator/coroutine is suspended, using the gi_yieldfrom / cr_await attributes. Teaching Task.get_stack to do this would be a nice little enhancement. -n -- Nathaniel J. Smith -- https://vorpus.org _______________________________________________ Async-sig mailing list Async-sig@python.org https://mail.python.org/mailman/listinfo/async-sig Code of Conduct: https://www.python.org/psf/codeofconduct/
