2.7 vs 3.3.3

[DannyPerrin]

I am learning python using 2.7 and much of the published materials is using 2.7. Why are we not using 3.3? what is the big difference?

[JasonScheirer]

Because 3.3 didn't come out until last September, and many third-party libraries ArcGIS depends on hadn't been ported to Python 3.x yet. For the most part, what you learn will translate between the two Python versions. On this page under Common Stumbling Blocks and Syntax Changes are the major things you need to keep in mind.