https://towardsdatascience.com/how-to-write-a-jupyter-notebook-extension-a63f9578a38c

Jupyter Notebook Extensions are simple add-ons which can significantly improve your productivity in the notebook environment. They automate tedious tasks such as formatting code or add features like creating a table of contents. While there are numerous existing extensions, we can also write our own extension to do extend the functionality of Jupyter.

In this article, we’ll see how to write a Jupyter Notebook extension that adds a default cell to the top of each new notebook which is useful when there are libraries you find yourself importing into every notebook. If you want the background on extensions, then check out this article. The complete code for this extension is available on GitHub.