Beginning Python Programming for Aspiring Web Developers

by Jeffrey Elkner (with liberal borrowings from the work of Allen Downey, and Peter Wentworth
An introductory computer programming text book using Python 3.

How to Think Like a Computer Scientist: Learning with Python

by Peter Wentworth, Jeffrey Elkner, Allen Downey, and Chris Meyers
An introductory computer science text book using Python.

Lessons in Electric Circuits

by Tony R. Kuphaldt
A free series of textbooks on the subjects of electricity and electronics