When you define a class in Python, the class definition itself becomes an object. For example:
class Foo(object): pass isinstance(Foo,object) # Returns True
If you think about this long enough, you will realize that something had to create the Foo object. This creation of the class object is controlled by a special kind of object called a metaclass. Simply stated, a metaclass is an object that knows how to create and manage classes.
In the preceding example, the metaclass that is controlling the creation of Foo is a class called type. In fact, if you display the type of Foo, you will find out that it is a type:
>>> print type(Foo) <type 'type'>
When a new class is defined with the class statement, a number of things happen. First, ...