I've probably been spoiled by the excellently written tutorial for Java's Swing. wxPython in Action just barely covers the necessities. It has slightly more content than what's available online, but the structure of it makes it highly unsuitable as a reference.
The book boasts numerous tables that list most commonly used methods or classes for each topic, but the list is not exhaustive. Coupled with the rapidly changing API, the lists are nearly useless. There are also no screenshots with the various widgets all shown for comparison purposes or just to figure out which one you want.
Sections are constructed around questions, such as "How can I use file picker?", or "What color names are predefined?" Which is fine usually, except sometimes, the authors merely cover a very specific question instead of properly introducing a new widget and its functionality.
There are numerous other examples of where the book falls short. Sizers, similar to Swing's LayoutManagers, get a very brief treatment, focusing mostly on the, in my opinion, rather useless GridSizer. Compare this with the Swing Tutorial's in-depth treatment of each individual LayoutManager.
Want to know how to handle mouse events like the scroll wheel? Tough luck, because there's absolutely nothing in the book about it. Instead, the book gives you the basics of event handling and probably expects you to look up the details of scroll wheel handling in the API docs online (which do not have example code).
Overall, this book may be fine for getting you started on a basic application, say, a GUI front-end to a database. Anything more advanced and you had better be ready to get down and dirty with the online API docs.