Metaclasses

Metaclass is a Python feature that is considered by many as one of the most difficult things to understand in this language and thus avoided by a great number of developers. In reality, it is not as complicated as it sounds once you understand a few basic concepts. As a reward, knowing how to use metaclasses grants you the ability to do things that are not possible without them.

Metaclass is a type (class) that defines other types (classes). The most important thing to know in order to understand how they work is that classes that define object instances are objects too. So, if they are objects, then they have an associated class. The basic type of every class definition is simply the built-in type class. Here is a simple diagram that should make this clear:

In Python, it is possible to substitute the metaclass for a class object with our own type. Usually, the new metaclass is still the subclass of the type class (refer to Figure 2) because not doing so would make the resulting classes highly incompatible with other classes in terms of inheritance:

Let's take a look at the general syntaxes for metaclasses in the next section.