异步函数不异步工作。

Question

我有个问题。

我编写了一个模拟http请求的简单代码：

from asyncio import sleep, run


async def get():
    print("Started get()")
    await sleep(3)
    print("Finished get()")


async def async_main():
    await get()
    await get()
    await get()


if __name__ == "__main__":
    run(async_main())

我希望结果应该是：

Started get()
Started get()
Started get()
(No output, just wait 3 seconds)
Finished get()
Finished get()
Finished get()

但结果是：

Started get()
(No output, just wait 3 seconds)
Finished get()
Started get()
(No output, just wait 3 seconds)
Finished get()
Started get()
(No output, just wait 3 seconds)
Finished get()

为什么会发生这种事？

Answer 1

您需要调度协同线，要么显式地使用asyncio.create_task()，要么隐式地使用asyncio.gather()。

from asyncio import sleep, run


async def get():
    print("Started get()")
    await sleep(3)
    print("Finished get()")


async def async_main():
    tasks = [asyncio.create_task(get()), 
             asyncio.create_task(get()),
             asyncio.create_task(get())]  # Explicit
    await asyncio.gather(*tasks)

async def async_main(): # Option 2
    await asyncio.gather(get(), get(), get())  # Implicit

if __name__ == "__main__":
    run(async_main())

Answer 2

只需异步运行任务，如下所示

async def async_main():
    await asyncio.gather(get(), get(), get())

if __name__ == "__main__":
    # run(async_main()) or
    asyncio.run(async_main())