asyncio.run() raise "RuntimeError: Event loop is closed" in a Jupyter Notebook

Question

I'm trying to run an async function inside a Jupyter Notebook using asyncio.run() like this:

import asyncio

async def my_task():
    await asyncio.sleep(1)
    return "Done"

asyncio.run(my_task())

But I get this error:

RuntimeError: Event loop is closed

I understand Jupyter uses an existing event loop, but what's the correct way to run async functions inside a notebook without this error?

Also:

Why does this work in a regular .py script but not in Jupyter?
Should I use nest_asyncio, await, or some other workaround?

I tested await my_task() and it works for me - so I solved problem in few second instead of wating few hours for answer ;) — furas
– furas, Commented Aug 7 at 11:17

Yokozuna · Accepted Answer · 2025-08-07 11:23:26Z

3

Instead of using asyncio.run(), just use await directly in the notebook cell:


import asyncio

async def my_task():
    await asyncio.sleep(1)
    return "Done"

await my_task()

In Jupyter, there is already an event loop running. Since you can’t run a new event loop when one is already running, you get this error.

answered Aug 7 at 11:23

Yokozuna

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1 Comment

No problem. Happy to help! :)