Other References:

A Course in  Number Theory and Cryptography, by Neal Koblitz, Springer-Verlag:  A more advanced mathematical treatment.

Introduction to Cryptography, PGP freeware introduction to the whole security infrastrucure - but no math.

Python.org/doc:  The official documentation, (starts with the Tutorial for programmers) and links to many other resources

The remaining links are more for programming beginners, but they might be useful:
Hands-on Python Tutorial:  My tutorial for Comp 150 - very slow, for total beginners, does not get to writing classes.
http://people.csail.mit.edu/pgbovine/python/, a cool site to visualize execution.  Good for the newbie, but also useful for class and object concepts.
Http://Codingbat.com/python  Coding practice site.  Intro programming level.