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A simple extension for Jupyter Notebook and Jupyter Lab to beautify Python code automatically using Black. Fork of dnanhkhoa/nb_black.

Project description


master: master branch build status

dev: dev branch build status

A simple extension for Jupyter Notebook and Jupyter Lab to beautify Python code automatically using Black. Fork of dnanhkhoa/nb_black with a few minor modifications:


Once loaded, automatically format syntactically correct jupyter cells with black once they are run.

Enhancements compared to dnanhkhoa/nb_black:

  • Configurability:
    • Try to read black config from pyproject.toml if available
    • Override settings such as line length and black.TargetVersion if desired
  • Uses black.format_cell to greatly simplify the codebase
  • Adds tests
  • Slightly more responsive (no longer requires setTimeout and a delay)
  • Free software: MIT


black is an extremely popular python formatter. Jupyter is an awesome way to run python. This extension helps you automatically blacken your jupyter.


  • Python >= 3.7
  • See setup.cfg


python3 -m venv .venv && source ./.venv/bin/activate
python3 -m pip install --upgrade pip
python3 -m pip install jupyter-black jupyter
python3 -m jupyter notebook

From here, there are two ways to load the extension:

Configurable (recommended):

import jupyter_black


To look at configuration options:


For example:

import black
import jupyter_black


The other way:

%load_ext jupyter_black

This will load the extension using your defaults from pyproject.toml if available, or use the black defaults. Please note that this defaults to lab=True, since moving to lab instead of standalone notebook installations seems to be the direction of the jupyter project; this means this method of loading will only work in JupyterLab, not in a standard notebook. For now, users running a standalone notebook (instead of lab) need to use the recommended (configurable) loading approach above.

Development Setup

  1. Clone the repo: git clone && cd jupyter-black
  2. Make a virtualenv: python3 -m venv .venv
  3. Activate venv, update pip, and install editable test/dev version:
$ source ./.venv/bin/activate
$ ./.venv/bin/python -m pip install --upgrade pip
$ ./.venv/bin/python -m pip install -e .[test,dev]


  • Tests use playwright
  • You'll need to run this command (once) prior to running the tests:
    • python -m playwright install --with-deps firefox
  • tox will automatically run these installation steps (helpful for CI)
  • If desired, pass the --no-headless flag to pytest for local debugging


Contribution ideas:

  • More tests, currently very basic
    • Ensure config is overridden in unsurprising ways
    • Ensure other config options are properly passed to black
    • Ensure that pyproject.toml is searched for properly
  • Write tests for jupyter lab, currently only tested for notebook
    • I think the fixture could easily be modularized to also work for lab, but haven't done the work yet


Please see and TODO.

Troubleshooting / FAQ

  • How can I install an older / specific version of jupyter black?
    • Install from a tag:
      • pip install git+git://
    • Install from a specific commit:
      • pip install git+git://


Many thanks to dnanhkhoa/nb_black for the original version!

And of course many thanks to the black and jupyter teams.

Also, after establishing the repo and reserving the name on PyPI, I noticed there is another library of the same name: drillan/jupyter-black. It looks like there have been no commits in the last 2 years, and it was never put in PyPI, so I think at this point I'll continue with this name. Sorry if this causes any trouble or confusion. I'll note that @drillan's library probably does things the right way by installing as an nbextension.

Buy Me a Coffee



0.3.4 :: 2023-04-27

0.3.2, 0.3.3 :: 2022-11-20

0.3.1 :: 2022-03-08

  • Fix description (thanks: @bryanwweber)
  • Version bump for PyPI

0.3.0 :: 2022-03-06

  • Default to lab=True
    • Add warning popup for users that load in notebook with lab=True (including via %load_ext)
    • Fix tests for the above
    • Might as well minor version bump since this changes the API, even if still 0.x

0.2.1 :: 20220-03-04

  • Python 3.10 support
  • Black 22 support

0.2.0 :: 2021-11-14

  • Breaking change: default to lab=True; %load_ext jupyter_black will now work in jupyterlab and no longer work in a standalone notebook

0.1.1 :: 2021-09-28

  • Unload the proper event

0.1.0 :: 2021-09-28

  • First release on PyPI.

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