Metaclass

That is, all metaclasses (such as Collection class, Object class and Set class) are instances of the class Metaclass. This is because all metaclasses have the same behavior. They define the structure, definition and behavior of a class.

First, the class can explicitly specify its metaclass by either setting a __metaclass__ class variable (Python 2), or supplying the metaclass keyword argument in the tuple of base classes (Python 3).