I just found this website:
http://pythonforbiologists.com/index.php/welcome-to-python-for-biologists/
it teaches you how to start programming with python for biologists. I even bought the pdf ebook for $39. I had a look at the book, and I think it is worthy. I went through first 4 chapters really fast, they are really basic but teach biologists in a really friendly way. I am even thinking to hold a bioinformatics training course in the future :) sounds ambitious, hmm..
Advanced topics can be found in the website:
Here is a link to a .zip file containing solutions to some of the exercises.
Section 1 : Large programs and complex data structures
Section 2 : Retrieving and sending information over the web
Section 3 : Large datasets and treelike data structures
Section 4 : Classes, modules and web applications
I've read the practical computing for biologists by Haddock Dunn http://www.amazon.com/Practical-Computing-Biologists-Steven-Haddock/dp/0878933913
it is a very good introductory book. Besides python, it also teaches you how to use linux command lines and some database basics. By the way, I wrote my first regular expression after reading the book.
well, I feel I just could get some practical problems ( text manipulation, Genomic Interval calculation using pybedtools, NGS by HTSeq) done by python though I began to play around with python in 04/24/2012. It takes time, but the investment definitely is rewarding!!