To clean `*.ipynb` files before git-commit.

.gitattribute

*.ipynb    filter=clean-ipynb

.gitconfig

[filter "clean-ipynb"]
  clean = clean-ipynb
  smudge = cat

clean-ipynb

#!/usr/bin/env python
import sys
import nbformat
import nbconvert

preprocessor = nbconvert.preprocessors.ClearOutputPreprocessor()
exporter = nbconvert.NotebookExporter()
exporter.register_preprocessor(preprocessor, enabled=True)
nb = nbformat.read(sys.stdin, nbformat.NO_CONVERT)
body, _ = exporter.from_notebook_node(nb)
print(body)