The Type Metaclass

If everything in Python is an object, then classes themselves must also be objects. This raises a question: what is the class of a class?

print(type(int))    # <class 'type'>
print(type(list))   # <class 'type'>
print(type(str))    # <class 'type'>

All classes are instances of type. This includes user-defined classes:

class Horse:
    pass

print(type(Horse))  # <class 'type'>

The Metaclass

type is Python's metaclass—the class that creates other classes. But what is the type of type itself?

print(type(type))  # <class 'type'>

type is an instance of itself. This self-referential relationship is the foundation of Python's object model.

Creating Classes Dynamically

Since type is a callable class, it can be used to create new classes at runtime. The constructor takes three arguments:

1. The class name (string)
2. A tuple of parent classes
3. A dictionary of class attributes

# Creating a class dynamically
Bar = type("Bar", (), {})
print(type(Bar))  # <class 'type'>

bar = Bar()
print(type(bar))  # <class '__main__.Bar'>

Inheritance and Attributes

Dynamic class creation supports inheritance and arbitrary attributes:

class Foo:
    pass

# Create a class that inherits from Foo with attributes
Foobar = type("Foobar", (Foo,), {"name": "Tim", "age": 25})

print(Foobar.__dict__)   # {..., 'name': 'Tim', 'age': 25}
print(Foobar.__bases__)  # (<class '__main__.Foo'>,)

foobar = Foobar()
print(foobar.name)              # Tim
print(isinstance(foobar, Foo))  # True

This capability enables advanced patterns like ORMs that generate model classes from database schemas, or testing frameworks that create mock classes dynamically.