Programming Python, Second Edition

Major Changes Between 1.3 and 1.5.2

This section describes significant language, library, tool, and C API changes in Python between the first edition of this book (Python 1.3) and Python release 1.5.2.

Core Language Changes

The following sections describe changes made to the Python language itself.

Pseudo-private class attributes

Python now provides a name-mangling protocol that hides attribute names used by classes. Inside a class statement, a name of the form _ _X is automatically changed by Python to _Class_ _X , where Class is the name of the class being defined by the statement. Because the enclosing class name is prepended, this feature limits the possibilities of name clashes when you extend or mix existing classes. Note that this is not a “private” mechanism at all, just a class name localization feature to minimize name clashes in hierarchies and the shared instance object’s namespace at the bottom of the attribute inheritance links chain.

Class exceptions

Exceptions may now take the form of class (and class instance) objects. The intent is to support exception categories. Because an except clause will now match a raised exception if it names the raised class or any of its superclasses, specifying superclasses allows try statements to catch broad categories without listing all members explicitly (e.g., catching a numeric-error superclass exception will also catch specific kinds of numeric errors). Python’s standard built-in exceptions are now classes (instead of strings) ...