I am a bioinformatician looking to improve my skills in software design (things like error handling, object-orientated design, unit testing and best practises in general).

My background is biology (my degree was in biology) and I am self taught in Bash, R and Python. Most software design books look quite complex or tend to use Java examples.

Does anyone know of a good book/website that has a "gentle" introduction to software design and that, ideally, rely on Python rather than Java?

Thanks.