IPKernelApp Error and Warning

JupyterLab
, ,
#1

I usually use the following command to start Jupyterlab:

jupyter lab --no-browser

After I start a browser, it immediately shows the following error and warning messages:

[IPKernelApp] ERROR | No such comm target registered: jupyter.widget.control
[IPKernelApp] WARNING | No such comm: 8d87f402-5faa-45c8-933f-e3560ac90fb7

Can someone please suggest how I can debug the error and warning? Thanks.

I am running Ubuntu 20.04.4 LTS on Windows WSL2. Jupyterlab version is 3.3.3 and ipython version is 8.2.0.

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#2

Hello kdlin1, assuming you work in a Python environment, can you please run $ python -m pip freeze and give us the resulting packages, their versions and whether this is a virtual environment (if so tell us what environment).

If you not working with Python, just issue $ jupyter --version on the cmd-line and edit your original post with the output.

If you solved the issue, please provide an answer for the community

#3

I can reproduce this on an NVIDIA Jetson (aarch64) - it’ll take me a couple of hours to trim things down to a minimal example. It doesn’t seem to be affecting the operation of my applications. Also, this environment is frozen at Python 3.6, so “get a newer Python” is not a solution.

#4

Hi, sorry for the late response. I use conda to manage the packages. Will your command still work?

#5

I run Python 3.8.13. The same problem is still there.

#6

It turns out this is an ipywidgets issue. It was fixed in 2017 but apparently some package constraint solvers still give a version that’s broken. See https://github.com/jupyter-widgets/ipywidgets/issues/1721. There’s a workaround here: https://github.com/jupyter-widgets/ipywidgets/issues/1721#issuecomment-330759036

You run that in your activated conda environment after you’ve installed everything.

#7

It is unclear to me what one needs to do to fix the issue you mentioned. Could you please elaborate a bit?

#8

According to the following Github issues, this error and warning are harmless. The project maintainers are working on a change that will result in these messages not being generated in the first place. More information can be read here:

And here:

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