> It is particularly odd to me that the dependents of all instances are stored in a dictionary that is a class variable. Just a note: these are class variables

> It is particularly odd to me that the dependents of all instances are stored in a dictionary that is a class variable. Just a note: these are class variables, not class instance variables. Class variables are a strange thing which is available from both class-side and instance-side methods. It's nice if you want to have a clean interface to both single element (via an instance) and to a collection (via a class).