- Chapter 18 from Think Python
- Chapter 8 from the Python Cookbook
- Zetcode's tutorial has a concise explanation of Inheritance, Polymorphism and Special Methods.
- Ultimate Magic Methods guide: http://www.rafekettler.com/magicmethods.html
- Raymond Hettinger's The Art of Subclassing from PyCon US 2012.
- Composability Through Multiple Inheritance from PyCon US 2013. Highly recommended. Talks about the Method Resolution Order and Composability through the use of Mixins.
- Python's MRO (Method Resolution Order)