Figure 1: Effective Python
Effective python is a very handy book to have around. It's setup in a way that allows you to quickly jump to the information you require and get some quick tips or just jog your memory. The information provided is relevant to both python 2 & 3, which I found quite interesting as it highlighted some of the improvements in python 3.
I particularly found the information on generators and co-routines very informative. The examples have inspired me to try and move to python 3, but unfortunately some of my projects still require a few third party libraries that only support python 2.
The information contained within is also relevant to web development, application development, mobile applications and scientific programming. Unlike a lot of python books it does not have a specific focus on web development and focuses more on the tools of the language and how to use them to your advantage, whatever you're working on.
You will likely find a lot of information you already know if you have worked with python for any length of time, however there are enough tips that developers will learn something new they can apply in the software they write.