Error: Object 'jupyter.widget' not found in registry

[MariuszJurowicz]

The error is thrown when more than one notebook panel is opened when Lab launch.
There are more than one kernel started and only one at the beginning has the eg. jupyter.widgets extension registered.
The error is thrown even when no 3rd party extension is used and the simple ipywidgets widget has to be rendered.

The error is thrown even when we try to send msg to comm, targeting the custom com_target that has been registered during the custom extension registration step.

Please see twosigma/beakerx#7520

[saulshanabrook]

How can we reproduce this?

[double-u-a]

Same for me, Error: Object 'jupyter.widget' not found in registry is thrown when I have more than one notebook panel open at launch.

Restarting with only one tab returns no errors.

[jasongrout]

I can't reproduce this either. I start up Lab with a workspace with three notebooks, and I see each kernel being connected to twice, and no error messages.

What versions of jupyter lab, ipywidgets, and the jlab widget manager do you have installed?

[double-u-a]

I performed the conda install jupyter lab and widgets installations this week, so what ever is currently on the conda channels, using Windows 10. I can confirm exact versions on Monday.

[double-u-a]

jupyter lab 0.34.9
ipywidgets 7.4.2

Known labextensions:
   app dir: C:\Apps\Anaconda\envs\ium\share\jupyter\lab
        @jupyter-widgets/jupyterlab-manager v0.37.4 enabled  ok

NB Running on Firefox 62 with UBlock Origin

[leogout]

Hello, same here:

$ jupyter labextension list
JupyterLab v0.34.0
Known labextensions:
   app dir: /root/miniconda3/share/jupyter/lab
@jupyter-widgets/jupyterlab-manager
        @jupyter-widgets/jupyterlab-manager v0.37.4  enabled  OK
@jupyterlab/plotly-extension
        @jupyterlab/plotly-extension v0.17.2  enabled  OK
plotlywidget
        plotlywidget v0.3.0  enabled  OK

$ pip list # curated a bit this one, ask for the full list if needed
Package             Version
------------------- ---------
conda               4.5.4
html5lib            1.0.1
ipykernel           4.8.2
ipython             6.4.0
ipython-genutils    0.2.0
ipywidgets          7.2.1
jsonschema          2.6.0
jupyter-client      5.2.3
jupyter-core        4.4.0
jupyterlab          0.34.0
jupyterlab-launcher 0.13.1
matplotlib          2.2.2
notebook            5.5.0
numpy               1.14.5
pandas              0.22.0
pip                 10.0.1
plotly              3.2.1
scipy               1.1.0
setuptools          39.2.0
widgetsnbextension  3.2.1

[asvetly]

After googling for a while without hope, I realized that I need

jupyter labextension install @jupyter-widgets/jupyterlab-manager

[remborg]

@jasongrout I have jupyterlab-manager (1.0.2) installed on Jupyter Lab (1.0.2) but still the issue.
I think I've managed to reproduce the bug though:

1. In a new notebook, create an ipywidget component :

from ipywidgets import Button
Button(description = 'Test')

2. Save the notebook and open it again in another tab with 'Editor'
3. Open the notebook and run the first cell, the bug should show on the debugger. You might have to run the cell a few times

In 'real life' the bug happens randomly after usually 30 minutes working in the notebook.

---

Edit:
It looks like multiple kernels with the same id are created (is this normal?) but only one of them sees the method registerCommTarget called (in /packages/services/src/kernel/default.ts).
When a comm message arrives, depending on the kernel instance it either works or breaks.

[jasongrout]

This may be fixed in #6929 and will be released in 1.1 next week. Can you test out the 1.1 release candidate and see if it solves the issue?

pip install --pre jupyterlab

or

conda install jupyterlab=1.1.0rc0 -c conda-forge/label/prerelease-jupyterlab

[remborg]

I've just tried the v1.1.0rc0 and it works perfectly :)
Thank you @jasongrout !

[jasongrout]

Great!

[creative-resort]

I'm experiencing the issue again with JupyterLab 1.0.2
Is there a regression?

[jasongrout]

No, there shouldn't be a regression. Can you update to 1.1.1?

This error is a very generic error with any number of causes, usually I think having to do with an installation issue. So it would be best to open a new issue (please follow the reporting diagnosis guide at https://jupyterlab.readthedocs.io/en/stable/getting_started/issue.html to get a reproducible scenario and gather relevant information)

[grisaitis]

To recap, is the solution to this issue to...

1. use jupyterlab >= 1.1
2. jupyter labextension install @jupyter-widgets/jupyterlab-manager

?

Or is the widgets manager not required?

Without manager, I saw this error with jupyterlab 1.1.1.