Update, June 2013: A newer 5th Edition of this book is available.
[September 2009] I'm happy to announce the release of the 4th Edition of the book Learning Python.
This new edition has been thoroughly updated and expanded to cover both Python 3.1 and 2.6, and present features that appear in each Python line. Specifically, it focuses on Python 3.X, but discusses 2.X differences along the way. Whether you're using 2.X, using 3.X, or stuck somewhere in between, you'll find this new edition tailored to your current and future needs.
In addition to language changes, this edition has been augmented with a new OOP tutorial chapter derived from live classes, as well as new advanced topic chapters that explore Unicode processing, managed attributes, decorators, and metaclasses. As such, it is a substantially more complete text.
As before, this book is designed to be an in-depth introduction to the core Python language, and work much like a self-paced class on Python fundamentals. Learning Python 4th Edition is available now, from all the usual places. O'Reilly's page listed below also offers it in a variety of searchable electronic forms -- PDF, .epub, Kindle-compatible .mobi, and the Safari online catalog.
For a reference companion to this book, see also the new book Python Pocket Reference, 4th Edition, released shortly after the new Learning Python. This book has been similarly updated for both Python 3.1 and 2.6, and serves as supplemental reference material.
In addition, the applications-focused book Programming Python 4th Edition is designed to be a follow-up to Learning Python. It covers what you can do with Python after you've mastered its language fundamentals. By moving on to explore common libraries and tools and present more complete example programs, Programming Python is intended to serve as the second of a two-book set.