I am running Xubuntu 20.04 (after upgrading from 19.04) as a guest on a VirtualBox VM in a Windows 10 host. After an apt install of the jupyter metapackage, I keep getting two errors. To reproduce them, I created a Python3 notebook with the following cells:

[1] import ipywidgets as widgets

[2] widgets.__version__

[3] widgets.IntSlider()

On running cell 1 or on re-opening the notebook the following appears in the terminal where I invoked jupyter notebook:

[IPKernelApp] ERROR | No such comm target registered: jupyter.widget.version

Cells 1 & 2 run fine. Cell 3 creates the widget and the widget seems to operate fine but the notebook and the jupyter notebook terminal show:

[IPKernelApp] WARNING | Widget Javascript not detected.  It may not be installed or enabled properly.

pip3 list (showing only relevant elements) results in:

jupyter-client               6.1.2         

jupyter-console              6.0.0         

jupyter-core                 4.6.3

ipykernel                    5.2.0         

ipython                      7.13.0        

ipython-genutils             0.2.0         

ipywidgets                   6.0.0

nbconvert                    5.6.1         

nbformat                     5.0.4 

notebook                     6.0.3

jupyter nbextension list shows:

  config dir: /home/marvin/.jupyter/nbconfig

    notebook section

      jupyter-js-widgets/extension  enabled 

      - Validating: OK

and after I tried: jupyter nbextension enable --py widgetsnbextension, the following was added:

  config dir: /etc/jupyter/nbconfig

    notebook section

      jupyter-js-widgets/extension  enabled 

      - Validating: OK

What is the best way of tracking down the problem? Or would I be better off doing one of the following:

1. re-installing via apt


2. re-installing via pip3


3. installing anaconda and re-installing via conda?

Many thanks

Marv