Black Jupyter Notebook

I was looking to auto format my notebooks with Black

I found a couple such as

• https://github.com/drillan/jupyter-black
• https://github.com/dnanhkhoa/nb_black
• https://github.com/csurfer/blackcellmagic
• https://github.com/tobinjones/jupyterlab_formatblack
• https://github.com/betatim/joli

However, they were all missing features, were out of date, and had issues.

Writing my own version would have been 2 short files, however, I found that code_prettify is so extensible that you can easily configure it to use Black using the nbextensions configurable parameters.

Features (and issues solved)

• skip jupyter magic lines
  • https://github.com/csurfer/blackcellmagic/issues/5
  • https://github.com/drillan/jupyter-black/issues/5
• configurable shortcuts
• adds a toolbar button
• runs for all selected cells
  • https://github.com/drillan/jupyter-black/issues/2
• can format whole notebook
• don’t have to run the cells
• don’t have to load ext each notebook
• don’t have to add notebook magics to each cell
• allowing for the cells to be edited while running
• deal with Black’s changing API and works with the most recent Black version, as well as previous ones
  • https://github.com/csurfer/blackcellmagic/issues/9
  • https://github.com/drillan/jupyter-black/issues/4
  • https://github.com/dnanhkhoa/nb_black/issues/2
• works with the most recent jupyter version
  • https://github.com/drillan/jupyter-black/issues/6

The python code I’ve written to do the black formatting is:

def black_reformat(cell_text):
    import black
    import re

    cell_text = re.sub("^%", "#%#", cell_text, flags=re.M)
    try:
        reformated_text = black.format_str(cell_text, 88)
    except TypeError:
        reformated_text = black.format_str(
            cell_text, mode=black.FileMode(line_length=88)
        )
    return re.sub("^#%#", "%", reformated_text, flags=re.M)

but code_prettify takes a json configuration file that runs javascript so here’s the json you need to paste into the configuration window:

To install

1. go to your Nbextensions in your jupyter notebook
   • to install nbextensions see https://github.com/ipython-contrib/jupyter_contrib_nbextensions#1-install-the-python-package
2. enable Code prettify
3. paste above json into text box labeled json defining library calls required to load the kernel-specific prettifying modules, and the prefix & postfix for the json-format string required to make the prettifying call.

This also requires black to be installed in the running kernel and it therefore goes without saying this only works in py>=3.6