Here's an interesting little language tidbit:

All "methods" of a class are functions. By definition, functions return a value, and procedures do not. In Python, there is no such thing as a procedure. A Python function implicitly returns None, if no other return statement is defined in the function.

IIRC, the word "method" came into use in OOP as a catch-all for OO languages that had both functions and procedures -- Java being a prime example. Since Python only has functions, it might be useful to mention this fact. It may or may not be useful to use the word "function" consistently rather than the word "method", because of this difference. On the other hand, this is an admittedly minor quibble, and perhaps does not belong in a book on patterns. A book on Python, though, should definitely mention this difference.