Codefolding

This extension adds codefolding functionality from CodeMirror to a codecell.

After clicking on the gutter (left margin of codecell) or typing Alt+F, the code gets folded. See the examples below. The folding status is saved in the cell metadata of the notebook, so reloading of a notebook will restore the folding view.

Supported modes

Three different folding modes are supported:

Indent Folding

Python-style code folding, detetects indented code.

The unfolded code above can be folded like this:

or this:

Bracket Folding

Other languages like Javascript use brackets to designate code blocks. Codefolding is supported for Javascript in using the %%javascript magic in a codecell.

Firstline Comment Folding

Allows collapsing of Python code cells to a single comment line. This is useful for long codecells. The algorithm simply looks for a comment in the first line and allows folding in the rest of the cell.

The code above can be folded like this:

Magics Folding

If you specify a magic in the first line of a cell, it can be folded, too.

Folded:

Internals

When saving a notebook, the folding information is saved in the metadata of each codecell. The number of the folding start line (beginning with 0) is stored in an array:

cell.metadata.code_folding = [ 3, 20, 33 ]

When reloading the notebook, the folding status is restored.

Exporting

To export a notebook containing folded cells, you will need to apply a custom preprocessor for nbconvert. The preprocessor is located in nbconvert_support/pre_codefolding.py.

The preprocessor is installed when you install the jupyter_contrib_nbextensions package. To activate the preprocessor manually, add the following lines to jupyter_nbconvert_config.py:

Exporter.preprocessors ='pre_codefolding.CodeFoldingPreprocessor'