On Mon, Jan 25, 2016 at 8:32 AM, Ian Kelly <ian.g.ke...@gmail.com> wrote: > > On Jan 25, 2016 2:04 AM, "Frank Millman" <fr...@chagford.com> wrote: >> >> "Ian Kelly" wrote in message >> news:calwzidngogpx+cpmvba8vpefuq4-bwmvs0gz3shb0owzi0b...@mail.gmail.com... >>> >>> This seems to be a common misapprehension about asyncio programming. >>> While coroutines are the focus of the library, they're based on >>> futures, and so by working at a slightly lower level you can also >>> handle them as such. So while this would be the typical way to use >>> run_in_executor: >>> >>> async def my_coroutine(stuff): >>> value = await get_event_loop().run_in_executor(None, >>> blocking_function, stuff) >>> result = await do_something_else_with(value) >>> return result >>> >>> This is also a perfectly valid way to use it: >>> >>> def normal_function(stuff): >>> loop = get_event_loop() >>> coro = loop.run_in_executor(None, blocking_function, stuff) >>> task = loop.create_task(coro) >>> task.add_done_callback(do_something_else) >>> return task >> >> >> I am struggling to get my head around this. >> >> 1. In the second function, AFAICT coro is already a future. Why is it >> necessary to turn it into a task? In fact when I tried that in my testing, I >> got an assertion error - >> >> File: "C:\Python35\lib\asyncio\base_events.py", line 211, in create_task >> task = tasks.Task(coro, loop=self) >> File: "C:\Python35\lib\asyncio\tasks.py", line 70, in __init__ >> assert coroutines.iscoroutine(coro), repr(coro) >> AssertionError: <Future pending ... > > > I didn't test this; it was based on the documentation, which says that > run_in_executor is a coroutine. Looking at the source, it's actually a > function that returns a future, so this may be a documentation bug.
And now I'm reminded of this note in the asyncio docs: """ Note: In this documentation, some methods are documented as coroutines, even if they are plain Python functions returning a Future. This is intentional to have a freedom of tweaking the implementation of these functions in the future. If such a function is needed to be used in a callback-style code, wrap its result with ensure_future(). """ IMO such methods should simply be documented as awaitables, not coroutines. I wonder if that's already settled, or if it's worth starting a discussion around. -- https://mail.python.org/mailman/listinfo/python-list
