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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

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I found a workaround and so am answering my own question...

I suspect the problem was that conflicting versions of jupyter-core were installed but I cannot prove this assertion, even when I asked the same question on Launchpad.

My solution was to uninstall all the pip3 and apt components and to delete my local configuration files. Next I installed MiniConda and created appropriate environments for my purposes using Conda. Now everything works perfectly.

(BTW: When using Conda, I recomment using separate environments for each project. If something goes wrong, it is easy to delete and start again and there seems to be less chance of conflicting binary files.)

Marv

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