Programming Python, by Mark Lutz is a serious book for those serious about programming in Python. A follow up to his book Learning Python, Programming Python covers none of the basics, but is entirely devoted to practical applications of the Python standard library. He starts off with representing records, and persistent storage, then introduces classes, console interaction, GUI programming, and web interfaces. The next several hundred pages provide practical examples of using system tools, file handling, parallelism, GUIs, networks, CGI scripting, databases, and basically anything else you can do with Python.
As an avid Pythonista, I had heard of this book a few times on mailing lists, and the list price of about $70 USD is probably the right price for this book if you're interested in using Python in a practical sense. However, for the current price of $40, this book is a steal. If you know the basics of Python and are wondering, "Now what?", you should buy this book.