Core Python Programming

10.5. *Exceptions as Classes

As we mentioned above, as of Python 1.5, all standard exceptions are now identified using classes. User-defined, class-based exceptions have been around for longer than that (since Python 1.2!), but until 1.5, the standard exceptions remained implemented as strings, mostly for backwards compatibility. However, there are a number of advantages that classes bring to the table, and these reasons were what finally led to all standard exceptions being converted from strings to class-based.

10.5.1. Selection via Object Identity

The search for an exception handler (checking each except clause) is accomplished via object identity and not object value. That means that if you are using string exceptions, the string object ...