There are two books which help me so much when I stat to write Python codes.
Python for bioinformatics of Sebastian Bassi (CRC press) and Bioinformatics Programming unsing Python of Michell L, Model (O'Reilly). This two books will show you what you can do with Python!
If I may suggest, depending on whether you're brand-new at coding or more experienced, you might focus on coding with Python in general (if you're a beginner), or focusing on modeling in an object-oriented language like Python. My personal experience is that the nature of the application (biology in your case) doesn't affect how you write the code, it just makes certain modeling styles make more or less sense, and thus partially determines how you set up your models (i.e., the conceptual relationship between your code and the real-world things it mimics/quantifies/processes/etc.).
If you're new to the Python language, I found John Zelle's textbook on Python to be great when I was first learning. Also, there's CodeAcademy online (http://www.codecademy.com/en/tracks/python). Make lots of use of StackOverflow, for pointers and help, too.
I don't know the books Luis suggested, but my guess is that they're more useful with regards to typical modeling methods in your field. But if you're a beginner, my suggestion is to start off with a general introduction and move onto themed material when you're comfortable with variable typing ("weakly" defined in Python), control statements like loops and conditional statements, objects and functions, and scripts. (Appologies if you know all about these already! :) ).