"Asyncio Event Loop is Closed" when getting loop

Question

When trying to run the asyncio hello world code example given in the docs:

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()

I get the error:

RuntimeError: Event loop is closed

I am using python 3.5.3.

score 110 · Answer 1 · answered Mar 23 '21 at 22:32

110

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())

answered Mar 23 '21 at 22:32

j4hangir

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I love StackOverflow. Thank you :) – Juanpa Jul 07 '21 at 20:32
4

This one did the trick for me, thanks a lot! – JustAnotherCoder Sep 06 '21 at 00:55
3

Thanks, but how did you even find this out? – Shryder Oct 06 '21 at 06:52
1

@Shryder Functional code started throwing this error after upgrading Python, I looked for what has changed between the python versions and saw the default EventLoopPolicy has been replaced (was mentioned somewhere in the docs). – j4hangir Nov 08 '21 at 00:21

Martijn Pieters · Accepted Answer · 2020-10-15T09:25:31.753

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.

If you still get `Event loop is closed` your code might be using a handle to the old event loop. — fuzzyTew, Jan 06 '21 at 13:08
author, do you mean change the snippet loop = asyncio.get_event_loop() to this: loop = asyncio.new_event_loop() ? — Serhii Kushchenko, Jul 21 '21 at 22:20
@SerhiiKushchenko: not sure what you are asking there. For the majority of Python code using asyncio, you want to use `asyncio.run()` to handle creating and running the loop, however. — Martijn Pieters, Jul 23 '21 at 18:06

score 8 · Answer 3 · edited Jan 18 '22 at 18:09

8

...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.

edited Jan 18 '22 at 18:09

skytaker

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answered Jan 18 '22 at 16:17

daviidarr

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windows event loop has very tight limitation on file descriptors number, https://stackoverflow.com/questions/47675410/python-asyncio-aiohttp-valueerror-too-many-file-descriptors-in-select-on-win – Gryu Feb 10 '22 at 12:37

"Asyncio Event Loop is Closed" when getting loop

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