On Mon, Nov 27, 2017 at 2:20 PM, David Mertz <me...@gnosis.cx> wrote: > Changing subject line because this is way off to the side. Guido and > Nathaniel point out that you can do everything yield expressions do with > async/await *without* an explicit event loop. While I know that is true, it > feels like the best case is adding fairly considerable ugliness to the code > in the process. > >> >> On Sat, Nov 25, 2017 at 3:37 PM, Guido van Rossum <gu...@python.org> >> wrote: >> > Maybe you didn't realize async/await don't need an event loop? Driving >> > an >> > async/await-based coroutine is just as simple as driving a >> > yield-from-based >> > one (`await` does exactly the same thing as `yield from`). > > >> >> On Sun, Nov 26, 2017 at 12:29 PM, Nathaniel Smith <n...@pobox.com> wrote: >> Technically anything you can write with yield/yield from could also be >> written using async/await and vice-versa, but I think it's actually >> nice to have both in the language. > > > Here is some code which is definitely "toy", but follows a pattern pretty > similar to things I really code using yield expressions: > > In [1]: from itertools import takewhile > In [2]: def injectable_fib(a=1, b=2): > ...: while True: > ...: new = yield a > ...: if new is not None: > ...: a, b = new > ...: a, b = b, a+b > ...: > In [3]: f = injectable_fib() > In [4]: list(takewhile(lambda x: x<200, f)) > Out[4]: [1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144] > In [5]: f.send((100,200)) > Out[5]: 200 > In [6]: list(takewhile(lambda x: x<1000, f)) > Out[6]: [300, 500, 800] > > > Imagining that 'yield' vanished from the language tomorrow, and I wanted to > write the same thing with async/await, I think the best I can come up with > is... actually, I just don't know who to do it without any `yield`. > > I can get as far as a slightly flawed: > > In [9]: async def atakewhile(pred, coro): > ...: l = [] > ...: async for x in coro: > ...: if pred(x): > ...: return l > ...: l.append(x) > > > But I just have no idea what would go in the body of > > async def afib_injectable(): > > > (that is, if I'm prohibited a `yield` in there) >
Honestly, this is one of Python's biggest problems when it comes to async functions. I don't know the answer to that question, and I don't know where in the docs I'd go looking for it. In JavaScript, async functions are built on top of promises, so you can just say "well, you return a promise, tada". But in Python, this isn't well documented. Snooping the source code for asyncio.sleep() shows that it uses @coroutine and yield, and I have no idea what magic @coroutine does, nor how you'd use it without yield. ChrisA _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
