This Python package is built in the book's repository and used in the notebooks when a visual aid is needed to explain a concept, but the code required to do so isn't relevant to the topic of discussion or could be confusing at that point of the book (i.e. if plotting hasn't been covered yet).
The visual_aids package is automatically installed when you use the requirements.txt file to set up the environment. However, for reference, it can be installed as follows (after cloning and activating your virtual environment):
(book_env) $ cd path/to/this/repo
(book_env) $ pip3 install visual-aidsCode involving this package is not included in the text since it only creates the visual aids, and we won't discuss the code behind them. The notebooks have all necessary code to generate the visual aids where necessary.