Try searching for: 'python aspect-oriented' as aspect oriented programming is about modifying existing class-methods (not exactly functions which is what you asked for). You might also do a search for "AOP considered harmful" http://www.infosun.fmi.uni-passau.de/st/papers/EIWAS04/stoerzer04aop_harmful.pdf
The main point is that when you are reading the source you don't know what the code is as it may be augmented by an "external" change. -- http://mail.python.org/mailman/listinfo/python-list
