python之asyncio.create_task 与等待

我无法理解 asyncio.create_task() 是如何工作的Python 3.7 中引入的函数应该可以工作。如果我这样做:

import asyncio 
 
async def helloworld(): 
    print("Hello world from a coroutine!") 
    asyncio.create_task(helloworld()) 
 
def main(): 
    loop = asyncio.get_event_loop() 
    loop.run_until_complete(helloworld()) 
 
if __name__ == "__main__": 
    main() 

我得到:

Hello world from a coroutine! Hello world from a coroutine!

作为输出(即协程运行两次)。这怎么不是无限递归呢？当我使用 await 时，我希望看到我所看到的关键词:

import asyncio 
 
 
async def helloworld(): 
    print("Hello world from a coroutine!") 
    await helloworld() 
 
 
def main(): 
    loop = asyncio.get_event_loop() 
    loop.run_until_complete(helloworld()) 
 
 
if __name__ == "__main__": 
    main() 

有了这个我得到:

Hello world from a coroutine! Hello world from a coroutine! Hello world from a coroutine! ... many more lines... Traceback (most recent call last): File "test3.py", line 53, in <module> main() File "test3.py", line 48, in main loop.run_until_complete(helloworld()) File "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/base_events.py", line 568, in run_until_complete return future.result() File "test3.py", line 37, in helloworld await helloworld() File "test3.py", line 37, in helloworld await helloworld() File "test3.py", line 37, in helloworld await helloworld() [Previous line repeated 984 more times] File "test3.py", line 36, in helloworld print("Hello world from a coroutine!") RecursionError: maximum recursion depth exceeded while calling a Python object

create_task怎么样了？仅被安排一次，您何时可以使用它的用例是什么(因为它必须在事件循环已经运行的上下文中运行)？

请您参考如下方法:

任务不会被安排一次，但循环只会运行到 helloworld 完成。您会看到消息打印两次，因为循环让下一个任务运行。之后，任务停止运行，因为循环不再运行。

如果你改变

loop.run_until_complete(helloworld()) 

到

loop.create_task(helloworld()) 
loop.run_forever() 

你会看到 Hello world from a coroutine! 重复打印出来。