{"id":204,"date":"2024-01-25T15:44:09","date_gmt":"2024-01-25T15:44:09","guid":{"rendered":"https:\/\/learnpython.elegantwallp.com\/?p=204"},"modified":"2024-01-25T15:46:39","modified_gmt":"2024-01-25T15:46:39","slug":"python-multiple-inheritance","status":"publish","type":"post","link":"https:\/\/learnpython.elegantwallp.com\/2024\/01\/25\/python-multiple-inheritance\/","title":{"rendered":"Python Multiple Inheritance"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you\u2019ll learn about Python multiple inheritance and how method order resolution works in Python.<\/p>\n\n\n\n

Introduction to the Python Multiple inheritance.<\/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\u2019ll 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:class ChildClass(ParentClass1, ParentClass2, ParentClass3): pass<\/code>Code language: Python (python)<\/small><\/p>\n\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\u2019s take an example to understand how multiple inheritance works:<\/p>\n\n\n\n

First, define a class\u00a0Car<\/code>\u00a0that has the\u00a0go()<\/code>\u00a0method:<\/p>\n\n\n\n

class Car: def go(self): print('Going')<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Second, define a class\u00a0Flyable<\/code>\u00a0that has the\u00a0fly()<\/code>\u00a0method:<\/p>\n\n\n\n
class Flyable: def fly(self): print('Flying')<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Third, define the\u00a0FlyingCar<\/code>\u00a0that inherits from both\u00a0Car<\/code>\u00a0and\u00a0Flyable<\/code>\u00a0classes:<\/p>\n\n\n\n
class FlyingCar(Flyable, Car): pass<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Since the\u00a0FlyingCar<\/code>\u00a0inherits from\u00a0Car<\/code>\u00a0and\u00a0Flyable<\/code>\u00a0classes, it reuses the methods from those classes. It means you can call the\u00a0go()<\/code>\u00a0and\u00a0fly()<\/code>\u00a0methods on an instance of the\u00a0FlyingCar<\/code>\u00a0class like this:<\/p>\n\n\n\n
if __name__ == '__main__': fc = FlyingCar() fc.go() fc.fly()<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
Going Flying<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Method resolution order (MRO)<\/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\u00a0start()<\/code>\u00a0method to the\u00a0Car<\/code>,\u00a0Flyable<\/code>, and\u00a0FlyingCar<\/code>\u00a0classes. In the\u00a0start()<\/code>\u00a0method of the\u00a0FlyingCar<\/code>\u00a0class, call the\u00a0start()<\/code>\u00a0method of the\u00a0super()<\/code>:<\/p>\n\n\n\n
class Car: def start(self): print('Start the Car') def go(self): print('Going') class Flyable: def start(self): print('Start the Flyable object') def fly(self): print('Flying') class FlyingCar(Flyable, Car): def start(self): super().start()<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Second, create an instance of the\u00a0FlyingCar<\/code>\u00a0class and call the\u00a0start()<\/code>\u00a0method:<\/p>\n\n\n\n
if __name__ == '__main__': car = FlyingCar() car.start()<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
Start the Flyable object<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
As you can see clearly from the output, the super().start()<\/code> calls the start()<\/code> method of the Flyable<\/code> class.<\/p>\n\n\n\n
The following shows the\u00a0__mro__<\/code>\u00a0of the\u00a0FlyingCar<\/code>\u00a0class:<\/p>\n\n\n\n
print(FlyingCar.__mro__)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
(<class '__main__.FlyingCar'>, <class '__main__.Flyable'>, <class '__main__.Car'>, <class 'object'>)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
From left to right, you\u2019ll 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>\u2018s 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\u00a0Flyable<\/code>\u00a0and\u00a0Car<\/code>\u00a0classes in the list, the\u00a0__mro__<\/code>\u00a0will change accordingly. For example:<\/p>\n\n\n\n
# Car, Flyable classes...<\/em> class FlyingCar(Car, Flyable): def start(self): super().start() if __name__ == '__main__': car = FlyingCar() car.start() print(FlyingCar.__mro__)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Output:<\/p>\n\n\n\n
Start the Car (<class '__main__.FlyingCar'>, <class '__main__.Car'>, <class '__main__.Flyable'>, <class 'object'>)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\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
Multiple inheritance & super<\/h2>\n\n\n\n
First, add the\u00a0__init__<\/code>\u00a0method to the\u00a0Car<\/code>\u00a0class:<\/p>\n\n\n\n
class Car: def __init__(self, door, wheel): self.door = door self.wheel = wheel def start(self): print('Start the Car') def go(self): print('Going')<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Second, add the\u00a0__init__<\/code>\u00a0method to the\u00a0Flyable<\/code>\u00a0class:<\/p>\n\n\n\n
class Flyable: def __init__(self, wing): self.wing = wing def start(self): print('Start the Flyable object') def fly(self): print('Flying')<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\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\u00a0__init__<\/code>\u00a0method to the\u00a0FlyingCar<\/code>\u00a0class:<\/p>\n\n\n\n
class FlyingCar(Flyable, Car): def __init__(self, door, wheel, wing): super().__init__(wing=wing) self.door = door self.wheel = wheel def start(self): super().start()<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
The method order resolution of the\u00a0FlyingCar<\/code>\u00a0class is:<\/p>\n\n\n\n
(<class '__main__.FlyingCar'>, <class '__main__.Flyable'>, <class '__main__.Car'>, <class 'object'>)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\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
Because the FlyingCar<\/code> class cannot access the __init__<\/code> method of the Car<\/code> class, you need to initialize the door<\/code>and wheel<\/code> attributes individually.<\/p>\n","protected":false},"excerpt":{"rendered":"
Summary: in this tutorial, you\u2019ll learn about Python multiple inheritance and how method order resolution works in Python. Introduction to the Python Multiple inheritance. When a class inherits from a single class, you have single inheritance. Python allows a class to inherit from multiple classes. If a class inherits from two or more classes, you\u2019ll have multiple inheritance. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[31],"tags":[],"class_list":["post-204","post","type-post","status-publish","format-standard","hentry","category-7-multiple-inheritance-descriptors"],"_links":{"self":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/204","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/comments?post=204"}],"version-history":[{"count":1,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/204\/revisions"}],"predecessor-version":[{"id":205,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/204\/revisions\/205"}],"wp:attachment":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/media?parent=204"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/categories?post=204"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/tags?post=204"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}