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Just like objects are created from classes, classes themselves are created from metaclasses. In short: - Class → creates objects - Metaclass → creates classes By default, Python uses the built-in metaclass ****"type"**** to create all classes. ## Steps to Create a Metaclass 1. ****Define a metaclass:**** Create a class that inherits from type. Optionally, define \_\_new\_\_ or \_\_init\_\_ to customize class creation. 2. ****Use the metaclass in a class:**** Specify metaclass=YourMeta when defining a class. 3. ****Class is created by the metaclass:**** The metaclass can modify attributes or methods of the class automatically. 4. ****Create instances of the class:**** Instances work normally, the metaclass only affects the class itself. Python `` ``` class Meta(type): ``` ``` def __new__(cls, name, bases, dct): ``` ``` dct['greet'] = lambda self: f"Hello from {name}!" ``` ``` return super().__new__(cls, name, bases, dct) ``` ``` ​ ``` ``` class Person(metaclass=Meta): ``` ``` def __init__(self, name): ``` ``` self.name = name ``` ``` ​ ``` ``` p = Person("Olivia") ``` ``` ​ ``` ``` print(p.greet()) ``` **Output** ``` Hello from Person! ``` ****Explanation:**** - ****Meta(type):**** Defines a metaclass that can modify classes when they are created. - ****\_\_new\_\_:**** Adds a greet method automatically to any class using this metaclass. - ****Person(metaclass=Meta):**** Class created using the metaclass, so it gets the greet method. - ****p = Person("Olivia"):**** Creates an instance of Person. - ****p.greet():**** Calls the method injected by the metaclass. ## Creating Subclass Subclasses can also be created dynamically using type. Python `` ``` def init(self, ftype): ``` ``` self.ftype = ftype ``` ``` ​ ``` ``` def getFtype(self): ``` ``` return self.ftype ``` ``` ​ ``` ``` FoodType = type('FoodType', (object,), { ``` ``` '__init__': init, ``` ``` 'getFtype': getFtype ``` ``` }) ``` ``` ​ ``` ``` def vegFoods(self): ``` ``` return {'Spinach', 'Bitter Guard'} ``` ``` ​ ``` ``` VegType = type('VegType', (FoodType,), { ``` ``` 'vegFoods': vegFoods ``` ``` }) ``` ``` ​ ``` ``` v = VegType("Vegetarian") ``` ``` print(v.getFtype()) ``` ``` print(v.vegFoods()) ``` **Output** ``` Vegetarian {'Bitter Guard', 'Spinach'} ``` ****Explanation:**** - VegType inherits from FoodType dynamically. - vegFoods method is added via the attributes dictionary. ## Metaclass Inheritance Metaclasses can be inherited just like normal classes. When a class inherits from a metaclass, it becomes an instance of that metaclass. Python `` ``` class MetaCls(type): ``` ``` pass ``` ``` ​ ``` ``` A = MetaCls('A', (object,), {}) ``` ``` class B(object): ``` ``` pass ``` ``` class C(A, B): ``` ``` pass ``` ``` ​ ``` ``` print(type(A)) ``` ``` print(type(B)) ``` ``` print(type(C)) ``` **Output** ``` <class '__main__.MetaCls'> <class 'type'> <class '__main__.MetaCls'> ``` ****Explanation:**** - A is created by MetaCls -\> type is MetaCls - B is normal -\> type is type - C inherits from A -\> type is MetaCls ## Metaclass Conflicts A class cannot inherit from two different metaclasses. Python will raise a TypeError. Python `` ``` class MetaCls(type): ``` ``` pass ``` ``` ​ ``` ``` A = MetaCls('A', (object,), {}) ``` ``` print("Type of A:", type(A)) ``` ``` ​ ``` ``` class B(object): ``` ``` pass ``` ``` print("Type of B:", type(B)) ``` ``` ​ ``` ``` class C(A, B): ``` ``` pass ``` ``` ​ ``` ``` print("Type of C:", type(C)) ``` ### Error: > TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases ****Explanation:**** - Python allows only one metaclass per class. - 'C' inherits from two different metaclasses → conflict occurs. ## Metaclass Use Cases Metaclasses are useful when you want to control class creation or enforce rules. ****1\. Class Verification:**** This example shows how a metaclass can enforce rules on class attributes. Python `` ``` class MainClass(type): ``` ``` def __new__(cls, name, bases, attrs): ``` ``` if 'foo' in attrs and 'bar' in attrs: ``` ``` raise TypeError(f"Class {name} cannot have both foo and bar") ``` ``` return super().__new__(cls, name, bases, attrs) ``` ``` ​ ``` ``` # This will raise an error ``` ``` class SubClass(metaclass=MainClass): ``` ``` foo = 42 ``` ``` bar = 34 ``` ****Explanation:**** - Ensures a class cannot have both foo and bar attributes. - Useful for interface enforcement. ****2\. Prevent Subclass Inheritance:**** This example shows how a metaclass can treat abstract classes differently, preventing certain checks for them while enforcing rules on normal classes. Python `` ``` class MetaCls(type): ``` ``` def __new__(cls, name, bases, attrs): ``` ``` if attrs.pop('abstract', False): ``` ``` print('Abstract Class:', name) ``` ``` return super().__new__(cls, name, bases, attrs) ``` ``` print('Normal Class:', name) ``` ``` return super().__new__(cls, name, bases, attrs) ``` ``` ​ ``` ``` class AbsCls(metaclass=MetaCls): ``` ``` abstract = True ``` ``` ​ ``` ``` class NormCls(metaclass=MetaCls): ``` ``` foo = 42 ``` **Output** ``` Abstract Class: AbsCls Normal Class: NormCls ``` ****Explanation:**** - Abstract classes can skip metaclass checks. - Normal classes are validated by the metaclass. ## Dynamic Generation of Classes Dynamic class generation allows you to create classes at runtime instead of defining them statically in code. Python `` ``` class FoodType: ``` ``` events = [] ``` ``` ​ ``` ``` def __init__(self, ftype, items): ``` ``` self.ftype = ftype ``` ``` self.items = items ``` ``` FoodType.events.append(self) ``` ``` ​ ``` ``` def run(self): ``` ``` print("Food Type:", self.ftype) ``` ``` print("Food Menu:", self.items) ``` ``` ​ ``` ``` @staticmethod ``` ``` def run_events(): ``` ``` for e in FoodType.events: ``` ``` e.run() ``` ``` ​ ``` ``` def sub_food(ftype): ``` ``` class_name = ftype.capitalize() ``` ``` def __init__(self, items): ``` ``` FoodType.__init__(self, ftype, items) ``` ``` globals()[class_name] = type(class_name, (FoodType,), {'__init__': __init__}) ``` ``` ​ ``` ``` # Create dynamic classes ``` ``` [ sub_food(ftype) for ftype in ["Vegetarian", "Nonvegetarian"] ] ``` ``` ​ ``` ``` Vegetarian(['Spinach', 'Bitter Guard']) ``` ``` Nonvegetarian(['Meat', 'Fish']) ``` ``` FoodType.run_events() ``` **Output** ``` Food Type: Vegetarian Food Menu: ['Spinach', 'Bitter Guard'] Food Type: Nonvegetarian Food Menu: ['Meat', 'Fish'] ``` ****Explanation:**** - 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Last Updated : 17 Feb, 2026 A metaclass in Python is a class that defines how other classes are created and behave. Just like objects are created from classes, classes themselves are created from metaclasses. In short: - Class → creates objects - Metaclass → creates classes By default, Python uses the built-in metaclass ****"type"**** to create all classes. ## Steps to Create a Metaclass 1. ****Define a metaclass:**** Create a class that inherits from type. Optionally, define \_\_new\_\_ or \_\_init\_\_ to customize class creation. 2. ****Use the metaclass in a class:**** Specify metaclass=YourMeta when defining a class. 3. ****Class is created by the metaclass:**** The metaclass can modify attributes or methods of the class automatically. 4. ****Create instances of the class:**** Instances work normally, the metaclass only affects the class itself. **Output** ``` Hello from Person! ``` ****Explanation:**** - ****Meta(type):**** Defines a metaclass that can modify classes when they are created. - ****\_\_new\_\_:**** Adds a greet method automatically to any class using this metaclass. - ****Person(metaclass=Meta):**** Class created using the metaclass, so it gets the greet method. - ****p = Person("Olivia"):**** Creates an instance of Person. - ****p.greet():**** Calls the method injected by the metaclass. ## Creating Subclass Subclasses can also be created dynamically using type. **Output** ``` Vegetarian {'Bitter Guard', 'Spinach'} ``` ****Explanation:**** - VegType inherits from FoodType dynamically. - vegFoods method is added via the attributes dictionary. Metaclasses can be inherited just like normal classes. When a class inherits from a metaclass, it becomes an instance of that metaclass. **Output** ``` <class '__main__.MetaCls'> <class 'type'> <class '__main__.MetaCls'> ``` ****Explanation:**** - A is created by MetaCls -\> type is MetaCls - B is normal -\> type is type - C inherits from A -\> type is MetaCls A class cannot inherit from two different metaclasses. Python will raise a TypeError. ### Error: > TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases ****Explanation:**** - Python allows only one metaclass per class. - 'C' inherits from two different metaclasses → conflict occurs. Metaclasses are useful when you want to control class creation or enforce rules. ****1\. Class Verification:**** This example shows how a metaclass can enforce rules on class attributes. ****Explanation:**** - Ensures a class cannot have both foo and bar attributes. - Useful for interface enforcement. ****2\. Prevent Subclass Inheritance:**** This example shows how a metaclass can treat abstract classes differently, preventing certain checks for them while enforcing rules on normal classes. **Output** ``` Abstract Class: AbsCls Normal Class: NormCls ``` ****Explanation:**** - Abstract classes can skip metaclass checks. - Normal classes are validated by the metaclass. ## Dynamic Generation of Classes Dynamic class generation allows you to create classes at runtime instead of defining them statically in code.