在 asyncio 中检索任务结果的正确方法

Question

我正在尝试检查 asyncio 模块的 wait 方法。我有这个原始的测试应用程序作为游乐场：

import asyncio

async def foo():
    return 1  # datetime.datetime.now()

async def entry_point():
    coros = [foo()]*3
    done, pending = await asyncio.wait(coros, return_when=asyncio.FIRST_COMPLETED)
    for obj in done:
        print(obj._result)  # works, but seem dirty

asyncio.run(entry_point())

基本上，我的目标是获得第一个完成任务的结果。在这里，我对术语有点困惑。文档说 asyncio.wait

Returns two sets of Tasks/Futures: (done, pending).

我如何知道对象是 task 还是 future？主要问题是，如何提取成功结束任务的结果？一种方法是访问受保护的属性 _result（如我的代码片段所示）。但我觉得有一种更简洁的方法可以做到这一点。实现该目标的正确模式是什么？

https://docs.python.org/3/library/asyncio-task.html#waiting-primitives

Answer 1

asyncio.wait 的文档有以下注释：

Deprecated since version 3.8, will be removed in version 3.11: Passing coroutine objects to wait() directly is deprecated.

因此你应该使用asyncio.Task that also has the asyncio.Task.result方法：

test.py:

import asyncio
import random


async def task(i):
    t = random.uniform(1, 5)
    print(f"START: {i} ({t:.3f}s)")
    await asyncio.sleep(t)
    print(f"END: {i}")

    return i


async def main():
    tasks = []

    for i in range(5):
        tasks.append(asyncio.create_task(task(i)))

    done, pending = await asyncio.wait(tasks, return_when=asyncio.FIRST_COMPLETED)

    for t in done:
        print(t.result())


if __name__ == "__main__":
    asyncio.run(main())

测试：

$ python test.py
START: 0 (2.743s)
START: 1 (2.490s)
START: 2 (4.785s)
START: 3 (3.746s)
START: 4 (1.010s)
END: 4
4

如果您想检索所有结果并首先获取最早的下一个结果，请改用asyncio.as_completed：

...
for t in asyncio.as_completed(tasks):
    print(await t)
...

测试 2：

$ python test.py
START: 0 (2.155s)
START: 1 (1.309s)
START: 2 (3.380s)
START: 3 (3.451s)
START: 4 (1.587s)
END: 1
1
END: 4
4
END: 0
0
END: 2
2
END: 3
3

在 asyncio 中检索任务结果的正确方法

Proper way to retrieve the result of tasks in asyncio

python-asyncio