Think Python is an introduction to Python programming for beginners. It starts with basic concepts of programming; it is carefully designed to define all terms when they are first used and to develop each new concept in a logical progression. Larger pieces, like recursion and object-oriented programming, are divided into a sequence of smaller steps and introduced over the course of several chapters.

It's author was kind enough to make it available on his website for free. You can read the book in PDF form from here or in HTML here.