Jupyter Notebook with Python 3.8 - NotImplementedError

Revising the answer in 2019

Change the end part of the file C:\Users\{USER-NAME}\AppData\Local\Programs\Python\Python38\Lib\asyncio\__init__.py

From

if sys.platform == 'win32':  # pragma: no cover
    from .windows_events import *
    __all__ += windows_events.__all__
else:
    from .unix_events import *  # pragma: no cover
    __all__ += unix_events.__all__

To

import asyncio

if sys.platform == 'win32':
    from .windows_events import *
    asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
    __all__ += windows_events.__all__
else:
    from .unix_events import *  # pragma: no cover
    __all__ += unix_events.__all__

EDIT

This issue exists in older versions of Jupyter Notebook and was fixed in version 6.0.3 (released 2020-01-21). To upgrade to the latest version run:

pip install notebook --upgrade

---

Following on this issue through GitHub, it seems the problem is related to the tornado server that jupyter uses.

For those that can't wait for an official fix, I was able to get it working by editing the file tornado/platform/asyncio.py, by adding:

import sys

if sys.platform == 'win32':
    asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

After the main imports.

I expect an official fix for this soon, however.

For me, I had to reinstall asyncio

pip install asyncio --upgrade

And upgrade the kernel package

pip install ipykernel --upgrade