ipywidgets not working after changing kernel

Environment data

• VS Code version: 1.61.2
• Jupyter Extension version (available under the Extensions sidebar): main branch
• Python Extension version (available under the Extensions sidebar): v2021.10.1365161279
• OS (Windows | Mac | Linux distro) and version: macOS 10.15.7
• Python and/or Anaconda version: 3.9
• Type of virtual environment used (N/A | venv | virtualenv | conda | …): venv
• Jupyter server running: Local

Expected behaviour

After changing kernel, cells with ipywidgets can be re-run to show the widgets.

Actual behaviour

After changing the kernel, ipywidgets stops working.

Steps to reproduce:

Given a notebook containing a single cell with this code:

import ipywidgets as w
w.IntSlider()

If you run it, it will show a widget. If you now change kernel, then change back to the original kernel, and then run it again it will no longer show a widget. If you close the notebook and re-open it, it will work.

[zpincus]

Sorry for not noting this above, but I can confirm that on v2021.10.1001414422 of the Jupyter extension, not only does ipywidgets work when changing kernels on the local server (which starts a new kernel every time), but it also works on remote servers when starting up new kernels. It’s only broken when connecting to an existing kernel on remote servers, so this is definitely progress 😃

[DonJayamanne]

@zpincus I’ve created an issue here https://github.com/microsoft/vscode-jupyter/issues/8179 Please could you confirm this works for local kernels, that way we can close this issue and track the work for remote kernels on #8179 and we’ll try to get that fixed in a recovery build.