Python Essential Reference, 4th Edition [Amazon]
Addison-Wesley Professional (July 19, 2009)
ISBN 0672329786; 717 pages
Now in its 4th edition, the Essential Reference was the first major reference book published for Python--originally appearing in 1999. It is meant to be a serious reference for working programmers. As such, it tries to provide detailed coverage of every Python language feature, especially advanced features that often get skipped in introductory books. It also provides expanded reference material for most of the most commonly used modules in the standard library. I primarily wrote this book for myself and use it on a regular basis in my day-to-day work. Others have also found it to be useful.
The Python Essential Reference hits the "sweet spot of concise usefulness." (9/10 rating) - Slashdot
"Python Essential Reference is exactly what the title says - it's *essential*... [It] is a book that you must have on your bookshelf." - Mike Riley [Dr. Dobb's Journal ]
"Every so often a book comes along that makes you ask yourself, "Gee, when was the last time I had my eyes checked?" David M. Beazley's Python: Essential Reference is just such a book."
"This is probably the best serious reference book for programmers since K&R's The C Programming Language."
"This is not a book that will see much use in my office. In fact, I think I'm going to put it out of sight -- just looking at it annoys me."
"This is the best programming book I have ever seen."
I am currently working on a 5th edition to the Essential Reference. This is a major update that will be targeting Python 3.7. Look for it in late 2018.