在Python3.6.1中调用loop.close asyncio.get_event_loop后无法创建新的事件循环

Question

In Python3.6.1 after calling loop.close() on a loop obtained from asyncio.get_event_loop(), can a new loop be created?

I've looked at other posts with answers for properly closing a loop, and also how to use task.cancel(), but have not been able to use any of those examples in a way that would let a new loop be created after the first was closed. I also tried explicitly setting executor and later calling executor.shutdown(wait=True), but that didn't help. I also tried 'del loop', and del a bunch of other things.

Documentation indicates that closing a an event loop is idempotent and irreversible. Does that also mean that a new loop cannot be created?

Here is some simple example code to demonstrate the issue: `

 #!/usr/bin/env python3.6 ''' To demonstrate an issue, the following code was adapted from: https://docs.python.org/3/library/asyncio-eventloop.html ''' import asyncio def hello_world(loop): print('Hello World') loop.stop() loop = asyncio.get_event_loop() loop.call_soon(hello_world, loop) loop.run_forever() # loop.close() ''' If the commented out loop.close() above is uncommented, the following code will fail with: Traceback (most recent call last): File "./aquestion.py", line 28, in <module> loopNew.call_soon(hello_world, loopNew) File "/Library/Frameworks/Python.framework/Versions/3.6/lib /python3.6/asyncio/base_events.py", line 573, in call_soon self._check_closed() File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/base_events.py", line 357, in _check_closed raise RuntimeError('Event loop is closed') RuntimeError: Event loop is closed ''' loopNew = asyncio.get_event_loop() loopNew.call_soon(hello_world, loopNew) loopNew.run_forever() 

`

Any attempts to answer my question would be appreciated.

Alternatively, would it be bad form to create an event loop, use it for a variety of purposes, and then just close that loop when the long running program is about to exit? This just seems wrong.

Answer 1

asyncio.get_event_loop returns the current loop. It pays no attention to the state of the loop. If you need a new loop after closing one, you can use asyncio.new_event_loop .

Be aware that getting a new loop won't affect subsequent calls to get_event_loop . If you'd like that to return your new loop instead of the original one (especially since you've probably closed it), you'll need to call asyncio.set_event_loop yourself.

import asyncio

async def f():
    await asyncio.sleep(0)

loop = asyncio.get_event_loop()
loop.run_until_complete(f())
loop.close()

loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)