B.9. The descriptor protocol

The descriptor protocol is an aspect of Python that is regarded as deep black magic, perhaps even more so than metaclasses. Like metaclasses, the rules are very simple once you understand them; it is just not very often that you need to explicitly implement them. The descriptor protocol is how properties, class methods, and static methods are implemented.

When an object is fetched from a class or instance dictionary, the __getattribute__ method checks for these methods and invokes them appropriately to fetch the object. This allows you to customize what happens when an object is accessed as a class or instance attribute. Table B.11 shows the descriptor protocol methods.