"RuntimeError: asyncio.run() cannot be called from a running event loop" in Spyder

Question

I am trying to learn about asyncio for a websockets client. Every piece of code I try gets the following error:

RuntimeError: asyncio.run() cannot be called from a running event loop

I have tried the most simple code and it always gives that RuntimeError. I tried installing the full anaconda distribution again, etc, and can´t find what the problem might be.

I am using Spyder 3.3.3 with Python 3.7.3

An example of code that should work:

import asyncio

async def main():
    print('hello')
    await asyncio.sleep(1)
    print('world')

asyncio.run(main())

Error message:

File "C:\Users\jmart\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 786, in runfile
  execfile(filename, namespace)
File "C:\Users\jmart\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 110, in execfile
  exec(compile(f.read(), filename, 'exec'), namespace)
File "C:/Users/jmart/Documents/asynk2.py", line 8, in <module>
  asyncio.run(main())
File "C:\Users\jmart\Anaconda3\lib\asyncio\runners.py", line 34, in run
  "asyncio.run() cannot be called from a running event loop")
RuntimeError: asyncio.run() cannot be called from a running event loop

Did you try to run the code form a terminal typing python3.7 asynk2.py? My guess is that Spyder is using an event loop to run its python console/interpreter which causes this issue... — Bakuriu
– Bakuriu, Commented May 15, 2019 at 16:53
Many thanks, that seems to be the issue, is there any way to solve this? — Javier Martin
– Javier Martin, Commented May 15, 2019 at 17:01
Adding import nest_asyncio and nest_asyncio.apply() seems to be one solution — Javier Martin
– Javier Martin, Commented May 15, 2019 at 17:13
Does this answer your question? "asyncio.run() cannot be called from a running event loop" when using Jupyter Notebook — mkrieger1
– mkrieger1, Commented Sep 7, 2022 at 10:39

Mikhail Gerasimov · Accepted Answer · 2019-05-15 19:21:43Z

30

It's a known problem related to IPython.

One way as you already found is to use nest_asyncio:

import nest_asyncio
nest_asyncio.apply()

The other one is to install older version of tornado:

pip3 install tornado==4.5.3

answered May 15, 2019 at 19:21

Mikhail Gerasimov

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4 Comments

Javier Martin Over a year ago

The first solution seems to give some running problems for me, installing the older version of tornado seems to work perfectly!

Blaze Over a year ago

Beware, nested run calls will starve out loops. This monkey patch is very fragile on python / stdlib upgrades.

cglacet Over a year ago

Is there any reason for not simply using await main() with spyder?

munizig Over a year ago

I've started having problems after upgrading databricks cluster to runtime 11.3 (it informs 3.9.5 on sys.version). My code was working perfectly on 10.5 version. Just added the nest_asyncio as above at the start of my notebook and it's resolved.

Stepan · Accepted Answer · 2021-01-13 05:55:53Z

15

Problem origin

Spyder runs its own event loop

print(asyncio.get_running_loop().is_running()) 
Returns: True

but only one is allowed per thread

cannot be called when another asyncio event loop is running in the same thread

That is why, when we try to create a new event loop with
asyncio.run(main()) it gives us an error:
RuntimeError: asyncio.run() cannot be called from a running event loop

Solution

Except what already proposed with nest_asyncio and tornado I came up with

Attach to an existing Spyder thread event loop by creating a new task

import asyncio

async def main():
    print('Hello world!')

asyncio.create_task(main())

Create new thread (by executing in external terminal) which allows to run our own event loop.
Top menu Run -> Run configuration per file... -> Execute in the external system terminal

Now the code runs in new terminal and works

import asyncio

async def main():
    print('Hello world!')
asyncio.run(main())

answered Jan 13, 2021 at 5:55

Stepan

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2 Comments

PythoNic Over a year ago

This is definetly the better answer. Perfect would be a interpreter-independent version with try: ....create_task(main()) except RuntimeError: asyncio.run(main()). This works fine in Spyder, but still produces some warnings in python shell :(

Joooeey Over a year ago

task = create_task(main()) swallows exceptions. So I added task.add_done_callback(lambda task: task.result()).

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