获取循环时“ Asyncio 事件循环已关闭”

当尝试运行文档中给出的 syncio hello world 代码示例时:

import asyncio


async def hello_world():
print("Hello World!")


loop = asyncio.get_event_loop()
# Blocking call which returns when the hello_world() coroutine is done
loop.run_until_complete(hello_world())
loop.close()

我得到了一个错误:

RuntimeError: Event loop is closed

我使用的是 python3.5.3。

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最佳答案

You have already called loop.close() before you ran that sample piece of code, on the global event loop:

>>> import asyncio
>>> asyncio.get_event_loop().close()
>>> asyncio.get_event_loop().is_closed()
True
>>> asyncio.get_event_loop().run_until_complete(asyncio.sleep(1))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/.../lib/python3.6/asyncio/base_events.py", line 443, in run_until_complete
self._check_closed()
File "/.../lib/python3.6/asyncio/base_events.py", line 357, in _check_closed
raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

You need to create a new loop:

loop = asyncio.new_event_loop()

You can set that as the new global loop with:

asyncio.set_event_loop(asyncio.new_event_loop())

and then just use asyncio.get_event_loop() again.

Alternatively, just restart your Python interpreter, the first time you try to get the global event loop you get a fresh new one, unclosed.

As of Python 3.7, the process of creating, managing, then closing the loop (as well as a few other resources) is handled for you when use asyncio.run(). It should be used instead of loop.run_until_complete(), and there is no need any more to first get or set the loop.

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On Windows seems to be a problem with EventLoopPolicy, use this snippet to work around it:

asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
asyncio.run(main())
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...and just in case:

import platform
if platform.system()=='Windows':
asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

If you ever deploy your code in the cloud it might avoid painful debug.


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