Python 3 Object-Oriented Programming - Third Edition

Demystifying the magic

You can copy and paste the subclass code without understanding it if you want to make abstract classes that fulfill this particular contract. We'll cover most of the unusual syntaxes in the book, but let's go over it line by line to get an overview:

    @classmethod 

This decorator marks the method as a class method. It essentially says that the method can be called on a class instead of an instantiated object:

    def __subclasshook__(cls, C): 

This defines the __subclasshook__ class method. This special method is called by the Python interpreter to answer the question: Is the class C a subclass of this class?

        if cls is MediaLoader: 

We check to see whether the method was called specifically on this class, rather than, ...