{"id":2743,"date":"2021-11-06T09:45:22","date_gmt":"2021-11-06T09:45:22","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=2743"},"modified":"2025-03-30T12:09:15","modified_gmt":"2025-03-30T12:09:15","slug":"python-multiple-inheritance","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-oop\/python-multiple-inheritance\/","title":{"rendered":"Python Multiple Inheritance"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about Python multiple inheritance and how method order resolution works in Python.<\/p>\n\n\n\n

Introduction to the Python Multiple inheritance. #<\/a><\/h2>\n\n\n\n

When a class<\/a> inherits from a single class, you have single inheritance<\/a>. Python allows a class to inherit from multiple classes. If a class inherits from two or more classes, you’ll have multiple inheritance.<\/p>\n\n\n\n

To extend multiple classes, you specify the parent classes inside the parentheses ()<\/code> after the class name of the child class like this:<\/p>\n\n\n

class<\/span> ChildClass<\/span>(ParentClass1, ParentClass2, ParentClass3)<\/span>:<\/span>\n   pass<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The syntax for multiple inheritance is similar to a parameter list in the class definition. Instead of including one parent class inside the parentheses, you include two or more classes, separated by a comma. <\/p>\n\n\n\n
Let’s take an example to understand how multiple inheritance works:<\/p>\n\n\n\n
First, define a class Car<\/code> that has the go()<\/code> method:<\/p>\n\n\n
class<\/span> Car<\/span>:<\/span>\n    def<\/span> go<\/span>(self)<\/span>:<\/span>\n        print('Going'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, define a class Flyable<\/code> that has the fly()<\/code> method:<\/p>\n\n\n
class<\/span> Flyable<\/span>:<\/span>\n    def<\/span> fly<\/span>(self)<\/span>:<\/span>\n        print('Flying'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, define the FlyingCar<\/code> that inherits from both Car<\/code> and Flyable<\/code> classes:<\/p>\n\n\n
class<\/span> FlyingCar<\/span>(Flyable, Car)<\/span>:<\/span>\n    pass<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Since the FlyingCar<\/code> inherits from Car<\/code> and Flyable<\/code> classes, it reuses the methods from those classes. It means you can call the go()<\/code> and fly()<\/code> methods on an instance of the FlyingCar<\/code> class like this:<\/p>\n\n\n
if<\/span> __name__ == '__main__'<\/span>:\n    fc = FlyingCar()\n    fc.go()\n    fc.fly()<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Going\nFlying<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Here’s the complete program:<\/p>\n\n\n
class<\/span> Car<\/span>:<\/span>\n    def<\/span> go<\/span>(self)<\/span>:<\/span>\n        print('Going'<\/span>)\n\nclass<\/span> Flyable<\/span>:<\/span>\n    def<\/span> fly<\/span>(self)<\/span>:<\/span>\n        print('Flying'<\/span>)        \n\n\nclass<\/span> FlyingCar<\/span>(Flyable, Car)<\/span>:<\/span>\n    pass<\/span>\n\nif<\/span> __name__ == '__main__'<\/span>:\n    fc = FlyingCar()\n    fc.go()\n    fc.fly()<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Going\nFlying<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Method resolution order (MRO) #<\/a><\/h2>\n\n\n\n
When the parent classes have methods with the same name and the child class calls the method, Python uses the method resolution order (MRO) to search for the right method to call. Consider the following example:<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
First, add the start()<\/code> method to the Car<\/code>, Flyable<\/code>, and FlyingCar<\/code> classes. In the start()<\/code> method of the FlyingCar<\/code> class, call the start()<\/code> method of the super()<\/code>:<\/p>\n\n\n
class<\/span> Car<\/span>:<\/span>\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        print('Start the Car'<\/span>)\n\n    def<\/span> go<\/span>(self)<\/span>:<\/span>\n        print('Going'<\/span>)\n\n\nclass<\/span> Flyable<\/span>:<\/span>\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        print('Start the Flyable object'<\/span>)\n\n    def<\/span> fly<\/span>(self)<\/span>:<\/span>\n        print('Flying'<\/span>)\n\n\nclass<\/span> FlyingCar<\/span>(Flyable, Car)<\/span>:<\/span>\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        super().start()<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, create an instance of the FlyingCar<\/code> class and call the start()<\/code> method:<\/p>\n\n\n
if<\/span> __name__ == '__main__'<\/span>:\n    car = FlyingCar()\n    car.start()<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Start the Flyable object<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The output indicates that the super().start()<\/code> calls the start()<\/code> method of the Flyable<\/code> class.<\/p>\n\n\n\n
The following shows the __mro__<\/code> of the FlyingCar<\/code> class:<\/p>\n\n\n
print(FlyingCar.__mro__)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
(<class<\/span> '__main__<\/span>.FlyingCar<\/span>'>, <class<\/span> '__main__<\/span>.Flyable<\/span>'>, <class<\/span> '__main__<\/span>.Car<\/span>'>, <class<\/span> 'object<\/span>'>)<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
From left to right, you’ll see the FlyingCar<\/code>, Flyable<\/code>, Car<\/code>, and object<\/code>.<\/p>\n\n\n\n
Note that the Car<\/code> and Flyable<\/code> objects inherit from the object<\/code> class implicitly. When you call the start()<\/code> method from the FlyingCar<\/code>‘s object, Python uses the __mro__<\/code> class search path.<\/p>\n\n\n\n
Since the Flyable<\/code> class is next to the FlyingCar<\/code> class, the super().start()<\/code> calls the start()<\/code> method of the FlyingCar<\/code> class.<\/p>\n\n\n\n
If you flip the order of Flyable<\/code> and Car<\/code> classes in the list, the __mro__<\/code> will change accordingly. For example:<\/p>\n\n\n
# Car, Flyable classes...<\/span>\n\n\nclass<\/span> FlyingCar<\/span>(Car, Flyable)<\/span>:<\/span>\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        super().start()\n\n\nif<\/span> __name__ == '__main__'<\/span>:\n    car = FlyingCar()\n    car.start()\n\n    print(FlyingCar.__mro__)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Start the Car\n(<class<\/span> '__main__<\/span>.FlyingCar<\/span>'>, <class<\/span> '__main__<\/span>.Car<\/span>'>, <class<\/span> '__main__<\/span>.Flyable<\/span>'>, <class<\/span> 'object<\/span>'>)<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the super().start()<\/code> calls the start()<\/code> method of the Car<\/code> class instead, based on their orders in the method order resolution.<\/p>\n\n\n\n
Here’s the complete program:<\/p>\n\n\n
class<\/span> Car<\/span>:<\/span>\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        print('Start the Car'<\/span>)\n\n    def<\/span> go<\/span>(self)<\/span>:<\/span>\n        print('Going'<\/span>)\n\n\nclass<\/span> Flyable<\/span>:<\/span>\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        print('Start the Flyable object'<\/span>)\n\n    def<\/span> fly<\/span>(self)<\/span>:<\/span>\n        print('Flying'<\/span>)\n\n\nclass<\/span> FlyingCar<\/span>(Flyable, Car)<\/span>:<\/span>\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        super().start()\n        \nif<\/span> __name__ == '__main__'<\/span>:\n    car = FlyingCar()\n    car.start()    \n    print(FlyingCar.__mro__)\n    \n   <\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Try it<\/a><\/p>\n\n\n\n
Output:<\/p>\n\n\n
Start the Flyable object\n(<class<\/span> '__main__<\/span>.FlyingCar<\/span>'>, <class<\/span> '__main__<\/span>.Flyable<\/span>'>, <class<\/span> '__main__<\/span>.Car<\/span>'>, <class<\/span> 'object<\/span>'>)<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Multiple inheritance & super #<\/a><\/h2>\n\n\n\n
First, add the __init__<\/code> method to the Car<\/code> class:<\/p>\n\n\n
class<\/span> Car<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, door, wheel)<\/span>:<\/span>\n        self.door = door\n        self.wheel = wheel\n\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        print('Start the Car'<\/span>)\n\n    def<\/span> go<\/span>(self)<\/span>:<\/span>\n        print('Going'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, add the __init__<\/code> method to the Flyable<\/code> class:<\/p>\n\n\n
class<\/span> Flyable<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, wing)<\/span>:<\/span>\n        self.wing = wing\n\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        print('Start the Flyable object'<\/span>)\n\n    def<\/span> fly<\/span>(self)<\/span>:<\/span>\n        print('Flying'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The __init__<\/code> of the Car<\/code> and Flyable<\/code> classes accept a different number of parameters. If the FlyingCar<\/code> class inherits from the Car<\/code> and Flyable<\/code> classes, its __init__<\/code> method needs to call the right __init__<\/code> method specified in the method order resolution __mro__<\/code> of the FlyingCar<\/code> class.<\/p>\n\n\n\n
Third, add the __init__<\/code> method to the FlyingCar<\/code> class:<\/p>\n\n\n
class<\/span> FlyingCar<\/span>(Flyable, Car)<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, door, wheel, wing)<\/span>:<\/span>\n        super().__init__(wing=wing)\n        self.door = door\n        self.wheel = wheel\n\n    def<\/span> start<\/span>(self)<\/span>:<\/span>\n        super().start()<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The method order resolution of the FlyingCar<\/code> class is:<\/p>\n\n\n
(<class<\/span> '__main__<\/span>.FlyingCar<\/span>'>, <class<\/span> '__main__<\/span>.Flyable<\/span>'>, <class<\/span> '__main__<\/span>.Car<\/span>'>, <class<\/span> 'object<\/span>'>)<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
the super().__init__()<\/code> calls the __init__<\/code> of the FlyingCar<\/code> class. Therefore, you need to pass the wing<\/code> argument to the __init__<\/code> method.<\/p>\n\n\n\n
If you don’t call super().__init__()<\/code> in the FlyingCar<\/code> class, it will not be able to initialize door<\/code> and wheel<\/code> attributes from the Car<\/code> class, leading to a potential error.<\/p>\n\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
    \n
  • Python multiple inheritance allows one class to inherit from multiple classes.<\/li>\n\n\n\n
  • The method order resolution defines the class search path to find the method to call.<\/li>\n<\/ul>\n
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