From http://docs.python.org/3.4/library/exceptions.html:

"... programmers are encouraged to at least derive new exceptions from the Exception class and not BaseException."

This wording had someone I've talked to recently thinking that user-defined exceptions should inherit *directly* from Exception.

Suggested rewording, dropping the "at least" qualification that as far as I can tell serves no real purpose:

"... programmers are encouraged to derive new exceptions from the Exception class or one of its subclasses, and not from BaseException."