Jupyter Notebook - Cannot Connect to Kernel

Question

I\'ve tried installing jupyter notebook using pip3 install jupyter. Every time i launch a new jupyter notebook, the notebook is unable to connect to the kernel. See screenshot b

Answer 1

I had the same issue where the kernel would simply not connect. Tried every solution, still no connection.

In the end I noticed some ValueError Exceptions being raised in the console where I started the jupyter client. The source of these exceptions was another python script in the same folder as the notebook.

Fixed the script. Fixed the notebook.

Answer 2

I simply just restarted the Anaconda program and opened a new Python 3 notebook, and Jupyter could connect. :)

Answer 3

I got this error:

from prompt_toolkit.eventloop import generator_to_async_generator
ImportError: cannot import name 'generator_to_async_generator' from 'prompt_toolkit.eventloop' (/Users/danielmlow/miniconda3/envs/pydra/lib/python3.7/site-packages/prompt_toolkit/eventloop/__init__.py)

So I upgraded prompt_toolkit:

pip install prompt_toolkit==3.0.

Answer 4

There is a likelihood that you've updated Tornado to 6.0.0 recently. Try reinstalling it to version 5.1.1. It just helped me. Lost 1 hour of precious Saturday time on this.

Answer 5

for linux and windows:

     just install ipython kernel

           "python3 -m pip install ipykernel"

           "python3 -m ipykernel install --user"

      then restart jupyter notebook that's it

Answer 6

I experienced a similar issue on my old PC converted into a Ubuntu 20.04 server, with Jupyterlab running under Jupyterhub. The issue appeared after installing Jupytext with the following command:

python3 -m pip install jupytext --upgrade

which non only installed Jupytext but also upgraded my system to Jupyterlab 2.2.9 and Jupyterhub 1.2.2 (among other packages updates).

After that, running a cell containing the simple code:

3 * 4

under any python 3.6 kernel or even R 3.6 or 4.0 kernel left me with the status message:

Kernel xxx connecting...

but never completing the connection nor the simple computation.

Neither re-installing Tornado to version 5.1.1., nor reinstalling ipywidgets, succeeded in solving the issue.

But finally downgrading Jupyterlab and Jupyterhub to (approximately) the original version numbers worked for me:

python3 -m pip install wheel jupyterhub==1.1.0 jupyterlab==2.1.0 ipywidgets

According to the command outputs, the following packages versions were actually applied:

Installing collected packages: wheel, jupyterhub
  Attempting uninstall: wheel
    Found existing installation: wheel 0.34.2
    Uninstalling wheel-0.34.2:
      Successfully uninstalled wheel-0.34.2
  Attempting uninstall: jupyterhub
    Found existing installation: jupyterhub 1.1.0
    Uninstalling jupyterhub-1.1.0:
      Successfully uninstalled jupyterhub-1.1.0
Successfully installed jupyterhub-1.2.2 wheel-0.36.1

And after restarting jupyterhub, all my kernels were working again.