André Caron added the comment: Hi there!
I've just stumbled upon this behavior and I was also surprised by the fact that the second await simply returns None. After fiddling around for a while, I noticed that if I wrap the coroutine object using asyncio.ensure_future() or asyncio.get_event_loop().create_task(), the same result/exception is returned by multiple await expressions. I haven't looked at the patch, but the intent to make the 2nd await raise a RuntimeError seems strange for several reasons: - it's inconsistent with the Future/Task interface; - it's quite common to await a 2nd time to get the coroutine result after calling asyncio.wait(...) using ALL_COMPLETED or FIRST_EXCEPTION; - as mentioned in the mailing list the await keyword in C#/Hack/JS which inspired the await keyword (as per PEP492) returns the result/exception multiple times. I put up a Gist that shows the inconsistency: https://gist.github.com/AndreLouisCaron/db2965aae095f5c85dd5 Here's an example of asyncio.wait() I was referencing: async def main() f1 = foo() f2 = bar() asyncio.wait([f1, f2], return_when=asyncio.FIRST_EXCEPTION) print('1:', await f1) print('2:', await f2) I also noticed that there seems to be some intent to avoid making a distinction between a normal function returning a future and a coroutine function from the point of view of the caller. If the patch is merged as is, I will always need to use asyncio.ensure_future() on all coroutine calls before asyncio.wait() because the result is inconsistent depending on the implementation of foo() and bar(): if they return futures, I'm OK, but if any of them is a proper coroutine function, I might get RuntimeError exceptions. Any chance you can consider changing the patch to make awaiting a coroutine's result multiple times a valid pattern? ---------- nosy: +André Caron _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue25887> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
