Python 2.4.2 is a bugfix release of Python 2.4 - Python 2.4 is now in bugfix-only mode, no new features are being added. More than 60 bugs have been squashed since Python 2.4.1, including bugs that prevented Python working properly on 64 bit AIX and HP/UX.
Python 2.4 has improve new language feature :
multi-line imports - when using imports in the form from foo import bar, baz, bing, bang, you can surround the imported names with brackets, and they can be split across lines. This is part of PEP 328.
Farewell to OverflowWarning - as documented in PEP 237, Python no longer generates OverflowWarnings.
function/method decorators - function and method decorators, first described in PEP 318, have been added to the language, using 'pie-decorator' syntax. Decorators are on the line before the 'def', and prefixed with an '@' sign. (PEP 318)
Assigning to None - the compiler now treats assigning to None as a SyntaxError.
Failed import cleanup - when a module import failed, versions of Python prior to 2.4a2 would leave a broken module in sys.modules - subsequent attempts to import the failing module would silently succeed, but use the broken module object. The import machinery now removes the failing module from sys.modules if the import fails.
The -m command line option - python -m modulename will find a module in the standard library, and invoke it. For example, python -m pdb is equivalent to python /usr/lib/python2.4/pdb.py
and another else most update built-in modules & fix bugs.