Metaclasses

Call a function automatically in a class definition:

Another common use of metaclass is to automatically register types in your program. Registration is useful for doing reverse lookups, where you need to map a simple identifier back to a corresponding class.

For example, say you want to implement your own serialized representation of a Python object using JSON. You need a way to take an object and turn it into a JSON string. Here, I do this generically by defining a base class that records the constructor parameters and turns them into a JSON dictionary.