This book actually consists of a series of Jupyternotebooks, which is a file format, recognizableby its .ipynb extension, which intermixes expository prose withprogramming code. It can be opened using theJupyterLab application, which runsin your browser. In the notebooks, code is stored inside code cellswhich can be modified and run at will, which encourages interactiveexploration and makes learning easier. This is what a code cell lookslike: