There are no plans to port calibre to python 3. Just google a bit there are far more books on python 2.x than on python 3.x. I've never actually read any python books (I learned python by programming in python) so I cant recommend any. But a good place to start is:
http://docs.python.org/2/tutorial/
And see:
http://wiki.python.org/moin/BeginnersGuide/Programmers