intercepting methods

[Skaperen]

intercepting/replacing (or adding) methods of existing builtin types is something i have generally wanted to do.  an example of what i mean is to replace the __repr__ method of type int (and long in python2) to convert in hexadecimal instead of decimal.  by adding i mean adding, to the class as a whole, not individual object instances, a new method attribute.

is this doable without hacking the interpreter source?  example types i want to do this with include bool, int, long, float.