Python 2.5.2 or python 2.7.1

I was wondering if I should use python 2.5.2 to program on dreamhost, or if I should use the latest version 2.7.1. I’m new to python and trying to learn it, and need to know how about setting up and using it on my account.

Does ‘by default’ mean that I don’t need to install anything server side if I just use python 2.5.2?