The code for the short demos in chapters 1, 2, and 3 does not have dependencies (except for the Python standard library).
The code for the Case Studies in chapters 13-18 depends on the simulation "framework" introduced in chapter 12. This common code is contained in the file "feedback.py". Place this file in the same directory as the case study you want to run, or add its location to the PYTHONPATH environment variable.