jupyter-cell-source

A tiny JupyterLab 4 extension that exposes the live source of a notebook cell, including unsaved edits, as a JupyterLab command result.

It exists because two things are true at once:

• jupyterlab-diff takes originalSource from the caller and does not compare it with the live cell. A stale originalSource silently overwrites unsaved edits on Accept/Reject.
• JupyterLab's /api/contents returns the saved file, not the in-memory buffer.

This command gives a caller (for example an agent driving jupyterlab-commands-toolkit) a reliable way to compare the live buffer with disk before opening a diff.

Requirements

• JupyterLab 4.x
• jupyterlab-commands-toolkit — provides execute_command and returns the command's result to the caller.

Command

research:get-cell-source

Arguments (both optional):

The visible tab is preferred. If you pass notebookPath and the current tab points elsewhere, the first matching tab is used.

Return value:

{
  "path": "analysis.ipynb",
  "cellId": "4d6ee618-c7c9-42ba-b3e9-3c1ed3783a03",
  "dirty": false,
  "source": "# cell source, exactly as stored in the model\n..."
}

On failure: {"error": "no_notebook" | "no_model" | "cell_not_found", ...}.

dirty is the document-level flag. To decide whether a specific cell is safe to diff, compare its source byte-for-byte with the same cell in the saved .ipynb.

Build

export PATH=/path/to/jupyter/env/bin:$PATH
jlpm install
jlpm build

The prebuilt extension is written to:

jupyter_cell_source/labextension/

Install from PyPI

pip install jupyter-cell-source

Then restart JupyterLab. If you have a conda-pypi source configured, the same wheel can be installed through conda.

Install from a local build

Copy the built extension into the JupyterLab labextensions directory:

PREFIX=$(python -c "import sys; print(sys.prefix)")
cp -r jupyter_cell_source/labextension \
  "$PREFIX/share/jupyter/labextensions/jupyter-cell-source"

For a conda/mamba environment, this installs into the environment prefix. Make sure python and jupyter come from the same environment.

Then restart JupyterLab and reload the page. Verify with:

jupyter labextension list | grep cell-source

Uninstall

rm -rf "$PREFIX/share/jupyter/labextensions/jupyter-cell-source"

Restart JupyterLab.

Notes

• Keep a single tab per notebook when driving jupyterlab-diff: that extension resolves notebookPath to the first matching widget, and duplicate tabs can make it fail silently. This command prefers the visible tab, but the diff extension does not.
• The command reads cell.sharedModel.getSource(). It does not save the document.

License

MIT