What is a Python metaclass?

A Python metaclass is a class that defines the behavior of other classes, essentially controlling how classes are created. Metaclasses allow for advanced customization of class creation, including modifying class attributes, adding methods, or enforcing certain design patterns.

class Meta(type):
def __new__(cls, name, bases, attrs):
    print(f"Creating class {name}")
    return super().__new__(cls, name, bases, attrs)

class MyClass(metaclass=Meta):
pass

# Output: Creating class MyClass

In this example, a metaclass Meta is defined that prints a message whenever a class is created. The class MyClass uses this metaclass, so the message is printed when MyClass is defined.

Metaclasses are a powerful feature in Python, often used in frameworks and libraries to provide dynamic behavior, enforce constraints, or implement domain-specific languages within Python.