"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.

Answer 1

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.