Update:

14-02-2021, the book's website http://www.mindview.net/Books/Python/ThinkingInPython.html is no longer online. We switched the download link to a copy.

Book excerpts:

Thinking in Python is, initially, a translation of Thinking in Patterns with Java, rather than an introduction to Python. You are expected to have your way through at least Learning Python (by Mark Lutz & David Ascher; OReilly, 1999) or an equivalent text before coming to this book.

In addition, you are assumed have more than just a grasp of the syntax of Python. You should have a good understanding of objects and what they're about, including polymorphism.

On the other hand, by going through this book you're going to learn a lot about object-oriented programming by seeing objects used in many different situations. If your knowledge of objects is rudimentary, it will get much stronger in the process of understanding the designs in this book.