Is your Python program running in Processing Python mode?
To understand how OSC works, you should run the server and client demos both in Processing as two different sketches to see the library in action. Get this working first and understand how it works (or the intended behavior before proceeding further). Next, investigate an OSC version on the python side (Start here) I have never tried this but I am willing to bet it will work.
As an alternative, you can run a flask application and setup a processing server and you will use simple HTTP. This is more standard and it should work off the bat.
Kf