404 error and no such comm target when trying to use ipywidgets

I installed ipywidgets 7.0.1 via conda into a conda root python3 environment. When starting a notebook, I get a 404 when trying to load the extension

404 GET /nbextensions/widgetsnbextension.js?v=20170918194201 (171.66.17.71) 3.38ms referer=<my nb server's host IP>/notebooks/<my notebook>.ipynb

Followed by an error from IPkernelApp when I try to create and show a widget

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

I shouldn’t have to manually enable the extension since I’m using conda, but I tried doing jupyter nbextension enable --py widgetsnbextension anyway, which did not solve this.

[tensionhead]

When starting a notebook, I get a 404 when trying to load the extension

I had exactly the same (and other) problem(s), however activating it didn’t help (“could not Validate”). This line solved it for me:

jupyter nbextension install --py widgetsnbextension --user

(I guess for your setup you should leave out the –user flag)

And then I did the activation step

jupyter nbextension enable --py widgetsnbextension

[jasongrout]

WIthin a day or two, we had identified and fixed the issue three years ago, as documented above and on #1721. Coming along and posting a snarky complaint three years later does not help move things forward for this issue or the community. We invite you to be uplifting and contribute to the solution, being respectful like everyone else on this issue, in the spirit of the code of conduct: https://github.com/jupyter/governance/blob/master/conduct/code_of_conduct.md#expected-behavior