python - 从异步中的两个协程中选择第一个结果

Question

问题

使用 Python 的 asyncio 模块，如何从多个协程中选择第一个结果？

例子

我可能想在等待队列时实现超时:

result = yield from select(asyncio.sleep(1),
                           queue.get())

类似操作

这类似于 Go's select或 Clojure's core.async.alt! .这有点像 asyncio.gather 的逆过程(收集就像all，选择就像any。)

Answer 1

简单的解决方案，通过使用 asyncio.wait 及其 FIRST_COMPLETED 参数:

import asyncio

async def something_to_wait():
    await asyncio.sleep(1)
    return "something_to_wait"

async def something_else_to_wait():
    await asyncio.sleep(2)
    return "something_else_to_wait"


async def wait_first():
    done, pending = await asyncio.wait(
        [something_to_wait(), something_else_to_wait()],
        return_when=asyncio.FIRST_COMPLETED)
    print("done", done)
    print("pending", pending)

asyncio.get_event_loop().run_until_complete(wait_first())

给出:

done {<Task finished coro=<something_to_wait() done, defined at stack.py:3> result='something_to_wait'>}
pending {<Task pending coro=<something_else_to_wait() running at stack.py:8> wait_for=<Future pending cb=[Task._wakeup()]>>}
Task was destroyed but it is pending!
task: <Task pending coro=<something_else_to_wait() running at stack.py:8> wait_for=<Future pending cb=[Task._wakeup()]>>