ipywidgets 8 doesn't work with custom kernelspec

[skkestrel]

Applies To

• Notebooks (.ipynb files)
• Interactive Window and/or Cell Scripts (.py files with #%% markers)

What happened?

Hello,

I'm using ipywidgets=8.1.7. I set up a custom kernelspec in a virtual environment (pyenv) as:

{
 "argv": [
  "python",
  "-m",
  "ipykernel_launcher",
  "-f",
  "{connection_file}"
 ],
 "display_name": "new python",
 "language": "python",
 "metadata": {
  "debugger": true
 }
}

which works normally, except for the fact that certain widgets (like tqdm.notebook.tqdm) don't work. I ran the following:

import tqdm.notebook

tqdm.notebook.tqdm(range(10))

Here's the error in vscode devtools:

Details that might be helpful for troubleshooting:

• I'm running this in WSL2.
• The error goes away when I downgrade to ipywidgets v7.
• The error also goes away when I use the regular "python environment" kernel instead of my custom kernelspec.
• The widget also works normally with ipywidgets v8, with my custom kernel, in jupyter lab outside of vscode.

VS Code Version

1.103.1

Jupyter Extension Version

2025.7.0

Jupyter logs

20:51:02.227 [error] Widget load failure {} [ 'jsdelivr.com', 'unpkg.com' ] {
  className: 'HTMLStyleModel',
  moduleName: '@jupyter-widgets/controls',
  moduleVersion: '2.0.0',
  isOnline: true,
  timedout: false,
  error: '{}'
}
20:51:02.279 [error] Widget load failure {} [ 'jsdelivr.com', 'unpkg.com' ] {
  className: 'HTMLStyleModel',
  moduleName: '@jupyter-widgets/controls',
  moduleVersion: '2.0.0',
  isOnline: true,
  timedout: false,
  error: '{}'
}
20:51:02.279 [error] Widget Error: Error: Failed to render widget 8888a12f5ef348949cac79ab8e7cf23e, Error: Module @jupyter-widgets/controls, semver range ^2.0.0 is not registered as a widget module

Coding Language and Runtime Version

Python 3.12

Language Extension Version (if applicable)

No response

Anaconda Version (if applicable)

No response

Running Jupyter locally or remotely?

N/A or Not sure

[DonJayamanne]

Thank you for filing this issue and sorry you are running into this.

Please could you enable logging as follows:

• Open settings & go into Jupyter->Logging
• Change the value to trace
• Reload VS Code,
• Attempt to repro the issue & then copy the output from the Jupyter output panel (use the command Jupyter: Show Output to get to the logs).

Please share the full logs

[skkestrel]

Sharing logs. Thanks!

23:01:34.234 [debug] Handle Execution of Cells 0 for Untitled-1.ipynb
23:01:34.235 [trace] Execute Notebook Untitled-1.ipynb. Step 1
23:01:34.235 [trace] Connect to Kernel Untitled-1.ipynb. Step 2
23:01:34.235 [trace] Connected to Kernel Untitled-1.ipynb. Step 3
23:01:34.235 [trace] executeCell 0. Step 4
23:01:34.235 [trace] Cell Index:0 sent to kernel
23:01:34.246 [trace] Start cell 0 execution @ 1755745294246 (clear output)
23:01:34.246 [debug] Kernel acknowledged execution of cell 0 @ 1755745294246
23:01:34.249 [trace] Cell 0 completed in 0.003s (start: 1755745294246, end: 1755745294249)
23:01:34.250 [trace] Cell 0 executed successfully
23:01:34.255 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:01:34.260 [trace] Widget Message: WidgetManager: Loading class ProgressStyleModel:@jupyter-widgets/controls:2.0.0
23:01:34.267 [trace] Version of IPyWidgets 7 determined after 0s
23:01:34.269 [trace] Widget Message: WidgetManager: Loading class FloatProgressModel:@jupyter-widgets/controls:2.0.0
23:01:34.271 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:01:34.271 [trace] Widget Message: WidgetManager: Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:01:34.281 [trace] Widget Message: WidgetManager: failed, Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:01:34.283 [trace] Widget Message: WidgetManager: failed, Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:01:34.283 [error] Widget load failure {} [ 'jsdelivr.com', 'unpkg.com' ] {
  className: 'HTMLStyleModel',
  moduleName: '@jupyter-widgets/controls',
  moduleVersion: '2.0.0',
  isOnline: true,
  timedout: false,
  error: '{}'
}
23:01:34.283 [trace] Widget Message: WidgetManager: Loading class HTMLModel:@jupyter-widgets/controls:2.0.0
23:01:34.283 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:01:34.287 [trace] Widget Message: WidgetManager: Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:01:34.334 [trace] Widget Message: WidgetManager: failed, Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:01:34.334 [trace] Widget Message: WidgetManager: failed, Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:01:34.334 [error] Widget load failure {} [ 'jsdelivr.com', 'unpkg.com' ] {
  className: 'HTMLStyleModel',
  moduleName: '@jupyter-widgets/controls',
  moduleVersion: '2.0.0',
  isOnline: true,
  timedout: false,
  error: '{}'
}
23:01:34.334 [trace] Widget Message: WidgetManager: Loading class HTMLModel:@jupyter-widgets/controls:2.0.0
23:01:34.334 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:01:34.335 [trace] Widget Message: WidgetManager: Loading class HBoxModel:@jupyter-widgets/controls:2.0.0
23:01:34.335 [trace] Widget Message: Received display data message 7eb93f72e715456f8c6cfb21a2973c6c
23:01:34.389 [trace] Widget Message: Waiting for model to be available before rendering it 7eb93f72e715456f8c6cfb21a2973c6c
23:01:34.389 [error] Widget Error: Error: Failed to render widget 7eb93f72e715456f8c6cfb21a2973c6c, Error: Module @jupyter-widgets/controls, semver range ^2.0.0 is not registered as a widget module

[skkestrel]

Hi, I'm updating with some new insights. I'm including full trace logs, including startup.

I find that the issue seems to not be with the custom kernelspec, but rather with a custom kernel. It seems that the first kernel loaded after reloading the window affects everything afterwards.

I think what is happening is:

• When the first loaded kernel is my custom kernel (which is a subclass of IPythonKernel), the ipywidgets version detected by vscode is 7, then an error occurs when trying to render certain widgets. This error remains for every new kernel afterwards, including the default python kernels.
• When the first loaded kernel is the standard Python kernel, the ipywidgets version detected by vscode is 8, so the widgets work normally afterwards. Then, even if I switch to my custom kernel, the widgets will continue to work.

In summary, is there something I need to implement in my custom kernel to teach vscode to detect the correct version of ipywidgets?

Success example (detected v8):

Visual Studio Code (1.103.1, wsl, desktop)
Jupyter Extension Version: 2025.7.0.
Python Extension Version: 2025.12.0.
Python Environment Extension Version: 1.2.0.
Pylance Extension Version: 2025.7.1.
Platform: linux (x64).
Home = /home/kz
Temp Storage folder ~/.vscode-server/data/User/globalStorage/ms-toolsai.jupyter/version-2025.7.0
Workspace folder ~/projects/koatl
23:22:39.324 [debug] Start refreshing Kernel Picker (1755746559324)
23:22:39.484 [debug] Get Custom Env Variables, Class name = Gm, completed in 160ms, has a truthy return value, Arg 1: undefined, Arg 2: "RunPythonCode"
23:22:39.484 [debug] Jupyter Paths /kernels: 
23:22:39.485 [debug] Kernel Spec Root Paths, /usr/share/jupyter/kernels, /usr/local/share/jupyter/kernels, ~/.local/share/jupyter/kernels
23:22:39.488 [debug] End refreshing Kernel Picker (1755746559324)
23:22:39.506 [debug] Start refreshing Interpreter Kernel Picker
23:22:39.506 [debug] Start refreshing Kernel Picker (1755746559506)
23:22:39.753 [debug] creating new code watcher with matching document file://~/projects/koatl/koatl-kernel/koatl_kernel/kernel.py
23:22:40.937 [trace] Conda file is conda
23:22:42.347 [trace] Python API env change detected, add => '~/.pyenv/versions/pyo3/bin/python'
23:22:42.347 [trace] Search for KernelSpecs in Interpreter ~/.pyenv/versions/pyo3/bin/python
23:22:42.357 [trace] Python API env change detected, add => '/usr/bin/python3'
23:22:42.357 [trace] Search for KernelSpecs in Interpreter /usr/bin/python3
23:22:42.365 [trace] Hiding default KernelSpec /python for interpreter ~/.pyenv/versions/pyo3/bin/python (KernelSpec file ~/.pyenv/versions/pyo3/share/jupyter/kernels/python3/kernel.json)
23:22:42.365 [trace] Kernels for interpreter ~/.pyenv/versions/pyo3/bin/python are .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#koatl.~/.pyenv/versions/pyo3/python./.~/.pyenv/versions/pyo3/bin/python3#-m#koatl_kernel#-f#{connection_file}, .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#mypy.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher, .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher
23:22:42.367 [trace] Python API env change detected, add => '/bin/python3'
23:22:42.367 [trace] Search for KernelSpecs in Interpreter /bin/python3
23:22:42.383 [debug] KernelProvider switched kernel to id = .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#mypy.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher
23:22:42.383 [debug] start the kernel, options.disableUI=true for Untitled-1.ipynb
23:22:42.402 [trace] Registering commtarget jupyter.widget
23:22:42.403 [debug] Controller selection change completed
23:22:42.440 [info] Starting Kernel (Python Path: ~/.pyenv/versions/pyo3/bin/python, Pyenv, 3.12.3) for 'Untitled-1.ipynb' (disableUI=true)
23:22:42.440 [trace] Creating raw notebook for resource 'Untitled-1.ipynb'
23:22:42.487 [debug] Launching kernel .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#mypy.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher for Untitled-1.ipynb in ~/projects/koatl with ports 9001, 9000, 9004, 9002, 9003
23:22:42.491 [trace] Python API env change detected, update => '~/.pyenv/versions/pyo3/bin/python'
23:22:42.491 [trace] Search for KernelSpecs in Interpreter ~/.pyenv/versions/pyo3/bin/python
23:22:42.496 [trace] Hiding default KernelSpec /python for interpreter ~/.pyenv/versions/pyo3/bin/python (KernelSpec file ~/.pyenv/versions/pyo3/share/jupyter/kernels/python3/kernel.json)
23:22:42.497 [debug] Get Custom Env Variables, Class name = Gm, completed in 3ms, has a truthy return value, Arg 1: "~/projects/koatl", Arg 2: "RunPythonCode"
23:22:42.497 [debug] Get Custom Env Variables, Class name = Gm, completed in 3ms, has a truthy return value, Arg 1: "Untitled-1.ipynb", Arg 2: "RunPythonCode"
23:22:42.554 [trace] Kernels for interpreter ~/.pyenv/versions/pyo3/bin/python are .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#koatl.~/.pyenv/versions/pyo3/python./.~/.pyenv/versions/pyo3/bin/python3#-m#koatl_kernel#-f#{connection_file}, .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#mypy.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher, .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher
23:22:42.568 [trace] Python API env change detected, add => '/mnt/c/Users/Kevin/miniconda3/python'
23:22:42.569 [trace] Search for KernelSpecs in Interpreter /mnt/c/Users/Kevin/miniconda3/python
23:22:42.577 [debug] Refreshed Environments
23:22:42.855 [debug] Got env vars from Python Ext in 361ms for ~/.pyenv/versions/pyo3/bin/python, with env var count 50.
23:22:42.855 [trace] Prepend PATH with python bin for ~/.pyenv/versions/pyo3/bin/python
23:22:42.856 [debug] Getting activated env variables, Class name = Ld, completed in 362ms, has a truthy return value, Arg 1: "~/projects/koatl", Arg 2: "~/.pyenv/versions/pyo3/bin/python", Arg 3: undefined
23:22:42.862 [info] Process Execution: ~/.pyenv/versions/pyo3/bin/python -m pip list
23:22:42.863 [debug] Got env vars from Python Ext in 369ms for ~/.pyenv/versions/pyo3/bin/python, with env var count 50.
23:22:42.863 [trace] Prepend PATH with python bin for ~/.pyenv/versions/pyo3/bin/python
23:22:42.863 [debug] Getting activated env variables, Class name = Ld, completed in 369ms, has a truthy return value, Arg 1: "Untitled-1.ipynb", Arg 2: "~/.pyenv/versions/pyo3/bin/python", Arg 3: undefined
23:22:42.867 [info] Process Execution: ~/.pyenv/versions/pyo3/bin/python -c "import ipykernel; print(ipykernel.__version__); print("5dc3a68c-e34e-4080-9c3e-2a532b2ccb4d"); print(ipykernel.__file__)"
23:22:42.872 [info] Process Execution: ~/.pyenv/versions/pyo3/bin/python -m ipykernel_launcher --f=/run/user/1002/jupyter/runtime/kernel-v33b703909f60a79e8e9d9020d46dbbfb6d9e2aa97.json
    > cwd: ~/projects/koatl
23:22:42.872 [debug] Kernel process 466528.
23:22:42.994 [trace] ipykernel version & path 6.30.1, ~/.pyenv/versions/pyo3/lib/python3.12/site-packages/ipykernel/__init__.py for ~/.pyenv/versions/pyo3/bin/python
23:22:43.149 [debug] Kernel output 466528: To connect another client to this kernel, use:
--existing /run/user/1002/jupyter/runtime/kernel-v33b703909f60a79e8e9d9020d46dbbfb6d9e2aa97.json
23:22:43.170 [debug] Waiting for Raw Session to be ready in postStartRawSession
23:22:43.170 [debug] Waiting for Raw session to be ready, status: connected
23:22:43.170 [trace] Raw session connected
23:22:43.170 [debug] Waited for Raw session to be ready & got status: connected
23:22:43.170 [debug] Successfully waited for Raw Session to be ready in postStartRawSession
23:22:43.170 [debug] Kernel status is 'unknown' before requesting kernel info and after ready
23:22:43.170 [debug] Sending request for kernelInfo
23:22:43.215 [trace] Got response for requestKernelInfo
23:22:43.215 [debug] Successfully completed postStartRawSession after 1 attempt(s) in 45ms
23:22:43.216 [trace] Executing silently Code (idle) = import sys as _VSCODE_sys\nprint(_VSCODE_sys.executable); del _VSCODE_sys
23:22:43.221 [trace] Executing silently Code (completed) = import sys as _VSCODE_sys\nprint(_VSCODE_sys.executable); del _VSCODE_sys with 1 output(s)
23:22:43.222 [trace] Started running kernel initialization for Untitled-1.ipynb
23:22:43.222 [trace] Executing silently Code (idle) = try:\nimport ipywidgets as _VSCODE_ipywidgets\nprint("e976ee50-99ed-4aba-9b6b-9dcd5634d07d:IPy
23:22:43.252 [trace] Executing silently Code (completed) = try:\nimport ipywidgets as _VSCODE_ipywidgets\nprint("e976ee50-99ed-4aba-9b6b-9dcd5634d07d:IPy with 1 output(s)
23:22:43.252 [trace] Determined IPyWidgets Version as 8
23:22:43.252 [trace] Version of IPyWidgets 8 determined after 0.849s
23:22:43.252 [trace] Executing silently Code (idle) = def __VSCODE_inject_module():\ndef __VSCODE_call_function(function, callback, data=None):
23:22:43.323 [trace] Executing silently Code (completed) = def __VSCODE_inject_module():\ndef __VSCODE_call_function(function, callback, data=None): with 0 output(s)
23:22:43.323 [debug] Requesting Kernel info
23:22:43.323 [trace] Got Kernel info
23:22:43.323 [trace] End running kernel initialization, now waiting for idle
23:22:43.323 [trace] Waiting for idle on (kernel): 2f2cf2f9-31a6-4a38-ada3-7795dae32f07 -> idle
23:22:43.324 [trace] Finished waiting for idle on (kernel): 2f2cf2f9-31a6-4a38-ada3-7795dae32f07 -> idle
23:22:43.324 [trace] End running kernel initialization, session is idle
23:22:43.324 [trace] Registering Kernel Completion Provider from kernel new python for language python
23:22:43.325 [trace] IPyWidgetScriptSource.initialize
23:22:43.325 [info] Kernel successfully started
23:22:43.326 [debug] getDataDirsImpl, Class name = Vr (started execution), Arg 1: "Untitled-1.ipynb", Arg 2: "~/.pyenv/versions/pyo3/bin/python"
23:22:43.327 [debug] Get Custom Env Variables, Class name = Gm, completed in 1ms, has a truthy return value, Arg 1: undefined, Arg 2: "RunPythonCode"
23:22:43.327 [debug] Jupyter Paths : 
23:22:43.327 [debug] Get Custom Env Variables, Class name = Gm, completed in 0ms, has a truthy return value, Arg 1: "Untitled-1.ipynb", Arg 2: "RunPythonCode"
23:22:43.327 [debug] Got env vars from Python Ext in 0ms for ~/.pyenv/versions/pyo3/bin/python, with env var count 50.
23:22:43.327 [trace] Prepend PATH with python bin for ~/.pyenv/versions/pyo3/bin/python
23:22:43.327 [debug] Getting activated env variables, Class name = Ld, completed in 0ms, has a truthy return value, Arg 1: "Untitled-1.ipynb", Arg 2: "~/.pyenv/versions/pyo3/bin/python", Arg 3: undefined
23:22:43.333 [info] Process Execution: ~/.pyenv/versions/pyo3/bin/python ~/.vscode-server/extensions/ms-toolsai.jupyter-2025.7.0-linux-x64/pythonFiles/printJupyterDataDir.py
23:22:43.343 [debug] Got an empty Jupyter Data Dir from ~/.pyenv/versions/pyo3/bin/python, stderr = undefined
23:22:43.344 [debug] getDataDirsImpl, Class name = Vr, completed in 18ms, has a truthy return value, Arg 1: "Untitled-1.ipynb", Arg 2: "~/.pyenv/versions/pyo3/bin/python", Return Value: <Uri:~/.local/share/jupyter>, <Uri:~/.pyenv/versions/pyo3/share/jupyter>, <Uri:/usr/local/share/jupyter>, <Uri:/usr/share/jupyter>
23:22:43.577 [debug] End refreshing Kernel Picker (1755746559506)
23:22:43.793 [trace] Web view is ready to receive widget messages
23:22:43.832 [error] Widget Error: Failed to access CDN https://unpkg.com/ after 0 attempt(s), TypeError: Failed to fetch
23:22:43.832 [trace] Widget Message: Received IPyWidgets_kernelOptions in ScriptManager
23:22:43.832 [trace] Widget Message: Received IPyWidgetMessages.IPyWidgets_kernelOptions
23:22:43.832 [trace] Widget Message: data-base-url set to https://vscode-remote%2Bwsl-002bubuntu-002d24-002e04.vscode-resource.vscode-cdn.net~/.vscode-server/extensions/ms-toolsai.jupyter-2025.7.0-linux-x64/temp/scripts/cb9f54dee74bed8b10fdef931a7e24972d9a55ac18c8aea2bb93f1f807cad209/jupyter
23:22:43.832 [trace] Widget Message: Received IPyWidgets_kernelOptions in ScriptManager
23:22:43.832 [trace] Widget Message: Received IPyWidgetMessages.IPyWidgets_kernelOptions
23:22:43.832 [trace] Widget Message: data-base-url set to https://vscode-remote%2Bwsl-002bubuntu-002d24-002e04.vscode-resource.vscode-cdn.net~/.vscode-server/extensions/ms-toolsai.jupyter-2025.7.0-linux-x64/temp/scripts/cb9f54dee74bed8b10fdef931a7e24972d9a55ac18c8aea2bb93f1f807cad209/jupyter
23:22:43.850 [trace] Widget Message: Received IPyWidget scripts [{"moduleName":"jupyter-matplotlib","scriptUri":"https://vscode-remote%2Bwsl-002bubuntu-002d24-002e04.vscode-resource.vscode-cdn.net~/.vscode-server/extensions/ms-toolsai.jupyter-2025.7.0-linux-x64/temp/scripts/cb9f54dee74bed8b10fdef931a7e24972d9a55ac18c8aea2bb93f1f807cad209/jupyter/nbextensions/jupyter-matplotlib/index","source":"local"}]
23:22:43.850 [trace] Widget Message: Source for IPyWidget jupyter-matplotlib found in local @ https://vscode-remote%2Bwsl-002bubuntu-002d24-002e04.vscode-resource.vscode-cdn.net~/.vscode-server/extensions/ms-toolsai.jupyter-2025.7.0-linux-x64/temp/scripts/cb9f54dee74bed8b10fdef931a7e24972d9a55ac18c8aea2bb93f1f807cad209/jupyter/nbextensions/jupyter-matplotlib/index.
23:22:43.850 [trace] Widget Message: Registering IPyWidget jupyter-matplotlib found in https://vscode-remote%2Bwsl-002bubuntu-002d24-002e04.vscode-resource.vscode-cdn.net~/.vscode-server/extensions/ms-toolsai.jupyter-2025.7.0-linux-x64/temp/scripts/cb9f54dee74bed8b10fdef931a7e24972d9a55ac18c8aea2bb93f1f807cad209/jupyter/nbextensions/jupyter-matplotlib/index.
23:22:44.424 [trace] Executing silently Code (idle) = def _VSCODE_getVariable(what_to_get, is_debugging, *args):\n# Query Jupyter server for the info a
23:22:44.425 [trace] Executing silently Code (idle) = def _VSCODE_getVariable(what_to_get, is_debugging, *args):\n# Query Jupyter server for the info a
23:22:44.444 [trace] Executing silently Code (completed) = def _VSCODE_getVariable(what_to_get, is_debugging, *args):\n# Query Jupyter server for the info a with 1 output(s)
23:22:44.461 [trace] Executing silently Code (completed) = def _VSCODE_getVariable(what_to_get, is_debugging, *args):\n# Query Jupyter server for the info a with 1 output(s)
23:22:47.781 [debug] Handle Execution of Cells 0 for Untitled-1.ipynb
23:22:47.782 [trace] Execute Notebook Untitled-1.ipynb. Step 1
23:22:47.782 [trace] Connect to Kernel Untitled-1.ipynb. Step 2
23:22:47.782 [trace] Connected to Kernel Untitled-1.ipynb. Step 3
23:22:47.782 [trace] executeCell 0. Step 4
23:22:47.784 [trace] Cell Index:0 sent to kernel
23:22:47.787 [trace] Start cell 0 execution @ 1755746567786 (clear output)
23:22:47.787 [debug] Kernel acknowledged execution of cell 0 @ 1755746567786
23:22:47.799 [trace] Cell 0 completed in 0.013s (start: 1755746567786, end: 1755746567799)
23:22:47.799 [trace] Cell 0 executed successfully
23:22:47.809 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:22:47.815 [trace] Version of IPyWidgets 8 determined after 0s
23:22:47.820 [trace] Widget Message: WidgetManager: Loading class ProgressStyleModel:@jupyter-widgets/controls:2.0.0
23:22:47.820 [trace] Widget Message: WidgetManager: Loading class FloatProgressModel:@jupyter-widgets/controls:2.0.0
23:22:47.821 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:22:47.829 [trace] Widget Message: Waiting for model to be available before rendering it 2c7d946651a040858beb95a11780e966
23:22:47.830 [trace] Widget Message: WidgetManager: Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:22:47.830 [trace] Widget Message: WidgetManager: Loading class HTMLModel:@jupyter-widgets/controls:2.0.0
23:22:47.834 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:22:47.839 [trace] Widget Message: WidgetManager: Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:22:47.845 [trace] Widget Message: WidgetManager: Loading class HTMLModel:@jupyter-widgets/controls:2.0.0
23:22:47.888 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class HBoxModel:@jupyter-widgets/controls:2.0.0
23:22:47.889 [trace] Widget Message: Received display data message 2c7d946651a040858beb95a11780e966
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class HBoxView:@jupyter-widgets/controls:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class HTMLView:@jupyter-widgets/controls:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class ProgressView:@jupyter-widgets/controls:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class HTMLView:@jupyter-widgets/controls:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class LayoutView:@jupyter-widgets/base:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class LayoutView:@jupyter-widgets/base:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class StyleView:@jupyter-widgets/base:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class LayoutView:@jupyter-widgets/base:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class StyleView:@jupyter-widgets/base:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class LayoutView:@jupyter-widgets/base:2.0.0
23:22:47.889 [trace] Widget Message: WidgetManager: Loading class StyleView:@jupyter-widgets/base:2.0.0

Error example (detected v7):

Visual Studio Code (1.103.1, wsl, desktop)
Jupyter Extension Version: 2025.7.0.
Python Extension Version: 2025.12.0.
Python Environment Extension Version: 1.2.0.
Pylance Extension Version: 2025.7.1.
Platform: linux (x64).
Home = /home/kz
Temp Storage folder ~/.vscode-server/data/User/globalStorage/ms-toolsai.jupyter/version-2025.7.0
Workspace folder ~/projects/koatl
23:24:48.487 [debug] Start refreshing Kernel Picker (1755746688487)
23:24:48.694 [trace] Search for KernelSpecs in Interpreter ~/.pyenv/versions/pyo3/bin/python
23:24:48.694 [trace] Search for KernelSpecs in Interpreter /usr/bin/python3
23:24:48.694 [trace] Search for KernelSpecs in Interpreter /bin/python3
23:24:48.695 [debug] Get Custom Env Variables, Class name = Gm, completed in 208ms, has a truthy return value, Arg 1: undefined, Arg 2: "RunPythonCode"
23:24:48.695 [debug] Jupyter Paths /kernels: 
23:24:48.696 [debug] Kernel Spec Root Paths, /usr/share/jupyter/kernels, /usr/local/share/jupyter/kernels, ~/.local/share/jupyter/kernels
23:24:48.707 [debug] Start refreshing Interpreter Kernel Picker
23:24:49.007 [debug] creating new code watcher with matching document file://~/projects/koatl/koatl-kernel/koatl_kernel/kernel.py
23:24:49.036 [trace] Hiding default KernelSpec /python for interpreter ~/.pyenv/versions/pyo3/bin/python (KernelSpec file ~/.pyenv/versions/pyo3/share/jupyter/kernels/python3/kernel.json)
23:24:49.037 [trace] Kernels for interpreter ~/.pyenv/versions/pyo3/bin/python are .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#koatl.~/.pyenv/versions/pyo3/python./.~/.pyenv/versions/pyo3/bin/python3#-m#koatl_kernel#-f#{connection_file}, .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#mypy.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher, .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher
23:24:50.111 [trace] Conda file is conda
23:24:50.168 [debug] KernelProvider switched kernel to id = .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#koatl.~/.pyenv/versions/pyo3/python./.~/.pyenv/versions/pyo3/bin/python3#-m#koatl_kernel#-f#{connection_file}
23:24:50.169 [debug] start the kernel, options.disableUI=true for Untitled-1.ipynb
23:24:50.186 [trace] Registering commtarget jupyter.widget
23:24:50.187 [debug] Controller selection change completed
23:24:50.187 [trace] Version of IPyWidgets 7 determined after 0.001s
23:24:50.188 [trace] Version of IPyWidgets 7 determined after 0.001s
23:24:50.196 [debug] Handle Execution of Cells 1 for Untitled-1.ipynb
23:24:50.245 [trace] Python API env change detected, update => '~/.pyenv/versions/pyo3/bin/python'
23:24:50.245 [trace] Search for KernelSpecs in Interpreter ~/.pyenv/versions/pyo3/bin/python
23:24:50.249 [trace] Hiding default KernelSpec /python for interpreter ~/.pyenv/versions/pyo3/bin/python (KernelSpec file ~/.pyenv/versions/pyo3/share/jupyter/kernels/python3/kernel.json)
23:24:50.254 [debug] Get Custom Env Variables, Class name = Gm, completed in 0ms, has a truthy return value, Arg 1: "~/projects/koatl", Arg 2: "RunPythonCode"
23:24:50.255 [info] Starting Kernel (Python Path: ~/.pyenv/versions/pyo3/bin/python, Pyenv, 3.12.3) for 'Untitled-1.ipynb' (disableUI=true)
23:24:50.256 [trace] Creating raw notebook for resource 'Untitled-1.ipynb'
23:24:50.257 [trace] Execute Notebook Untitled-1.ipynb. Step 1
23:24:50.257 [trace] Connect to Kernel Untitled-1.ipynb. Step 2
23:24:50.309 [trace] Kernels for interpreter ~/.pyenv/versions/pyo3/bin/python are .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#koatl.~/.pyenv/versions/pyo3/python./.~/.pyenv/versions/pyo3/bin/python3#-m#koatl_kernel#-f#{connection_file}, .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#mypy.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher, .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94.~/.pyenv/versions/pyo3/python.~/.pyenv/versions/pyo3/python.-m#ipykernel_launcher
23:24:51.078 [trace] Web view is ready to receive widget messages
23:24:51.078 [error] Widget Error: Failed to access CDN https://unpkg.com/ after 0 attempt(s), TypeError: Failed to fetch
23:24:51.236 [trace] Python API env change detected, add => '/mnt/c/Users/Kevin/miniconda3/python'
23:24:51.236 [trace] Search for KernelSpecs in Interpreter /mnt/c/Users/Kevin/miniconda3/python
23:24:51.427 [debug] Launching kernel .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#koatl.~/.pyenv/versions/pyo3/python./.~/.pyenv/versions/pyo3/bin/python3#-m#koatl_kernel#-f#{connection_file} for Untitled-1.ipynb in ~/projects/koatl with ports 9001, 9000, 9004, 9002, 9003
23:24:51.427 [info] Launching Raw Kernel Koatl # ~/.pyenv/versions/pyo3/bin/python3
23:24:51.427 [debug] Create ProcessService, Class name = Hm (started execution), Arg 1: "Untitled-1.ipynb", Arg 2: {"a":false,"b":{"A":3,"z":{"i":-1,"end":0},"w":[{"id":930},{"id":931},null,{"id":934}]}}
23:24:51.429 [debug] Get Custom Env Variables, Class name = Gm, completed in 1ms, has a truthy return value, Arg 1: "Untitled-1.ipynb", Arg 2: "RunPythonCode"
23:24:51.556 [debug] Get Custom Env Variables, Class name = Gm, completed in 129ms, has a truthy return value, Arg 1: "Untitled-1.ipynb", Arg 2: "RunNonPythonCode", Arg 3: {"a":false,"b":{"A":4,"z":{"i":-1,"end":0},"w":[{"id":930},{"id":931},null,{"id":934},{"id":1144}]}}
23:24:51.556 [debug] Create ProcessService, Class name = Hm, completed in 129ms, has a truthy return value, Arg 1: "Untitled-1.ipynb", Arg 2: {"a":false,"b":{"A":4,"z":{"i":-1,"end":0},"w":[{"id":930},{"id":931},null,{"id":934},{"id":1144}]}}
23:24:51.698 [debug] Refreshed Environments
23:24:51.806 [debug] Got env vars from Python Ext in 378ms for ~/.pyenv/versions/pyo3/bin/python, with env var count 50.
23:24:51.806 [trace] Prepend PATH with python bin for ~/.pyenv/versions/pyo3/bin/python
23:24:51.807 [debug] Getting activated env variables, Class name = Ld, completed in 379ms, has a truthy return value, Arg 1: "Untitled-1.ipynb", Arg 2: "~/.pyenv/versions/pyo3/bin/python", Arg 3: {"a":false,"b":{"A":3,"z":{"i":-1,"end":0},"w":[{"id":930},{"id":931},null,{"id":934},null]}}
23:24:51.814 [info] Process Execution: ~/.pyenv/versions/pyo3/bin/python3 -m koatl_kernel -f /run/user/1002/jupyter/runtime/kernel-v3d1d0439b15d8e30a295a3fc6b887ca2fdebc65f3.json
    > cwd: ~/projects/koatl
23:24:51.814 [debug] Kernel process 476134.
23:24:51.818 [debug] Got env vars from Python Ext in 1564ms for ~/.pyenv/versions/pyo3/bin/python, with env var count 50.
23:24:51.818 [trace] Prepend PATH with python bin for ~/.pyenv/versions/pyo3/bin/python
23:24:51.818 [debug] Getting activated env variables, Class name = Ld, completed in 1564ms, has a truthy return value, Arg 1: "~/projects/koatl", Arg 2: "~/.pyenv/versions/pyo3/bin/python", Arg 3: undefined
23:24:51.824 [info] Process Execution: ~/.pyenv/versions/pyo3/bin/python -m pip list
23:24:52.080 [debug] Kernel output 476134: NOTE: When using the `ipython kernel` entry point, Ctrl-C will not work.

To exit, you will have to explicitly quit this process, by either sending
"quit" from a client, or using Ctrl-\ in UNIX-like environments.

To read more about this, see https://github.com/ipython/ipython/issues/2049


To connect another client to this kernel, use:
    --existing /run/user/1002/jupyter/runtime/kernel-v3d1d0439b15d8e30a295a3fc6b887ca2fdebc65f3.json

23:24:52.102 [debug] Waiting for Raw Session to be ready in postStartRawSession
23:24:52.102 [debug] Waiting for Raw session to be ready, status: connected
23:24:52.102 [trace] Raw session connected
23:24:52.102 [debug] Waited for Raw session to be ready & got status: connected
23:24:52.102 [debug] Successfully waited for Raw Session to be ready in postStartRawSession
23:24:52.102 [debug] Kernel status is 'unknown' before requesting kernel info and after ready
23:24:52.103 [debug] Sending request for kernelInfo
23:24:52.140 [trace] Got response for requestKernelInfo
23:24:52.140 [debug] Successfully completed postStartRawSession after 1 attempt(s) in 37ms
23:24:52.142 [trace] Started running kernel initialization for Untitled-1.ipynb
23:24:52.142 [debug] Requesting Kernel info
23:24:52.143 [trace] Got Kernel info
23:24:52.143 [trace] End running kernel initialization, now waiting for idle
23:24:52.143 [trace] Waiting for idle on (kernel): de6d57d6-a6ca-475b-a823-f601d1c4b143 -> idle
23:24:52.143 [trace] Finished waiting for idle on (kernel): de6d57d6-a6ca-475b-a823-f601d1c4b143 -> idle
23:24:52.143 [trace] End running kernel initialization, session is idle
23:24:52.143 [warn] Kernel completions not enabled for 'Koatl (pyo3)'. 
To enable Kernel completion for this language please add the following setting 
jupyter.completionTriggerCharacters = {koatl: [<List of characters that will trigger completions>]}. 
For more information please see https://aka.ms/vscodeJupyterCompletion
23:24:52.144 [trace] IPyWidgetScriptSource.initialize
23:24:52.144 [info] Kernel successfully started
23:24:52.144 [warn] No nbextensions folder found for kernel .jvsc74a57bd0966d8e46172e8fd70abb827f555239527ded0ab35d5d7f273affe80bd875ad94#koatl.~/.pyenv/versions/pyo3/python./.~/.pyenv/versions/pyo3/bin/python3#-m#koatl_kernel#-f#{connection_file}
23:24:52.145 [trace] Connected to Kernel Untitled-1.ipynb. Step 3
23:24:52.145 [trace] executeCell 1. Step 4
23:24:52.146 [trace] Cell Index:1 sent to kernel
23:24:52.151 [trace] Start cell 1 execution @ 1755746692150 (clear output)
23:24:52.151 [debug] Kernel acknowledged execution of cell 1 @ 1755746692150
23:24:52.162 [trace] Widget Message: Received IPyWidgets_kernelOptions in ScriptManager
23:24:52.162 [trace] Widget Message: Received IPyWidgetMessages.IPyWidgets_kernelOptions
23:24:52.346 [trace] Cell 1 completed in 0.196s (start: 1755746692150, end: 1755746692346)
23:24:52.346 [trace] Cell 1 executed successfully
23:24:52.350 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:24:52.358 [trace] Widget Message: WidgetManager: Loading class ProgressStyleModel:@jupyter-widgets/controls:2.0.0
23:24:52.358 [trace] Version of IPyWidgets 7 determined after 0.001s
23:24:52.362 [trace] Widget Message: WidgetManager: Loading class FloatProgressModel:@jupyter-widgets/controls:2.0.0
23:24:52.362 [trace] Widget Message: Waiting for model to be available before rendering it 4c26eeb37bc547b2ad5a418f22ba54c5
23:24:52.371 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:24:52.372 [trace] Widget Message: WidgetManager: Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:24:52.374 [trace] Widget Message: WidgetManager: failed, Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:24:52.374 [trace] Widget Message: WidgetManager: failed, Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:24:52.374 [error] Widget load failure {} [ 'jsdelivr.com', 'unpkg.com' ] {
  className: 'HTMLStyleModel',
  moduleName: '@jupyter-widgets/controls',
  moduleVersion: '2.0.0',
  isOnline: true,
  timedout: false,
  error: '{}'
}
23:24:52.376 [trace] Widget Message: WidgetManager: Loading class HTMLModel:@jupyter-widgets/controls:2.0.0
23:24:52.446 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:24:52.446 [trace] Widget Message: WidgetManager: Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:24:52.446 [trace] Widget Message: WidgetManager: failed, Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:24:52.446 [trace] Widget Message: WidgetManager: failed, Loading class HTMLStyleModel:@jupyter-widgets/controls:2.0.0
23:24:52.446 [error] Widget load failure {} [ 'jsdelivr.com', 'unpkg.com' ] {
  className: 'HTMLStyleModel',
  moduleName: '@jupyter-widgets/controls',
  moduleVersion: '2.0.0',
  isOnline: true,
  timedout: false,
  error: '{}'
}
23:24:52.446 [trace] Widget Message: WidgetManager: Loading class HTMLModel:@jupyter-widgets/controls:2.0.0
23:24:52.446 [trace] Widget Message: WidgetManager: Loading class LayoutModel:@jupyter-widgets/base:2.0.0
23:24:52.447 [trace] Widget Message: WidgetManager: Loading class HBoxModel:@jupyter-widgets/controls:2.0.0
23:24:52.447 [trace] Widget Message: Received display data message 4c26eeb37bc547b2ad5a418f22ba54c5
23:24:52.447 [error] Widget Error: Error: Failed to render widget 4c26eeb37bc547b2ad5a418f22ba54c5, Error: Module @jupyter-widgets/controls, semver range ^2.0.0 is not registered as a widget module
23:24:52.697 [debug] End refreshing Kernel Picker (1755746688487)

[DonJayamanne]

I don't think the kernel spec you have shared is correct.
Based on the logs its running something like koatl_kernel and thats not in your kernel spec file you shared.
Please can you check if you have a kernel spec in you workspace folder and share that.

Process Execution: ~/.pyenv/versions/pyo3/bin/python3 -m koatl_kernel -f /run/user/1002/jupyter/runtime/kernel-v3d1d0439b15d8e30a295a3fc6b887ca2fdebc65f3.json

This line indicates there's another kernel spec file thats in use, apart from what you have shared.

[skkestrel]

right, here is the kernelspec

{"argv": ["/home/kz/.pyenv/versions/pyo3/bin/python3", "-m", "koatl_kernel", "-f", "{connection_file}"], "display_name": "Koatl", "language": "koatl"}

I see that the issue is here -

vscode-jupyter/src/kernels/kernel.ts

Line 891 in df05eeb

if (!isPythonKernelConnection(this.kernelConnectionMetadata)) {

non-python kernels have the ipywidgets version set by 7 to default. Will it be possible to have my kernel output the detected ipywidgets version on startup and the extension can listen for that instead of querying actively?

[DonJayamanne]

I'll update the minimum version of IPYWidgets for non-python kernels as well.
Its been over 2 years since we decided to fall back to version 7 for non-python.
8 has been around for a while.

[skkestrel]

thank you very much!