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Python Multiple Inheritance


Inheritance can be done in a number of ways. Till now, we have seen examples where a single class inherits another class.

We can also create a subclass of another subclass.

multiple inheritance in Python

For example, a class Shape has a subclass Rectangle, and the class Rectangle has a subclass Square. In this case, Square will inherit the properties of Rectangle as well as Shape.

class Shape():
    # code
	
class Rectangle(Shape):
    # code
	
class Square(Rectangle):
    # code

We also know that a class can have more than one subclass.

multiple inheritance in Python

For example, a class Shape has two subclasses Rectangle and Circle. Here, both Rectangle and Circle will inherit the properties of Shape.

class Shape():
    # code
	
class Rectangle(Shape):
    # code
	
class Circle(Shape):
    # code

Let’s see an example having the above two scenarios of inheritance.

class Shape():
    def m(self):
        print("This is Shape")
	
class Rectangle(Shape):
    def m1(self):
        print("This is Rectangle")
	
class Circle(Shape):
    def m2(self):
        print("This is Circle")

class Square(Rectangle):
    def m3(self):
        print("This is Square")
		
r = Rectangle()  # creating object r of subclass Rectangle
c = Circle()  # creating object c of subclass Circle
s = Square()  # creating object s of subclass Square

r.m1()
r.m()

print("****")

c.m2()
c.m()

print("****")

s.m3()
s.m1()
s.m()
Output
This is Rectangle
This is Shape
****
This is Circle
This is Shape
****
This is Square
This is Rectangle
This is Shape

In this example, Shape has two subclasses Rectangle and Circle, and thus the objects of Rectangle and Circle can access the methods of their respective classes as well as the method of the parent class Shape. Rectangle further has a subclass Square and so the object of Square can access the method of Square and the methods of its ancestor classes Rectangle and Shape.

This was pretty straightforward, right?

In Python, a class can have more than one parent class. So, it inherits the properties of all its parent classes.

multiple inheritance in Python

For example, a class Deer is a subclass of two classes - Animal and Herbivorous. So, it will inherit the properties of both its parent classes.

class Animal():
    # code

class Herbivorous():
    # code

class Deer(Animal, Herbivorous):
    # code
# superclass
class Animal():
    def m1(self):
        print("This is  parent class Animal")

# superclass
class Herbivorous():
    def m2(self):
        print("This is  parent class Herbivorous")

# subclass		
class Deer(Animal, Herbivorous):
    def m(self):
        print("This is child class Deer")
		
deer = Deer()

deer.m()
deer.m1()
deer.m2()
Output
This is child class Deer
This is parent class Animal
This is parent class Herbivorous

Here, the class Deer has two parent classes Animal and Herbivorous. Thus, its object deer can access both its parent classes’ methods m1() and m2().

Look at another example.

class Area():
    def getArea(self, l, b):
        return l * b

class Perimeter():
    def getPerimeter(self, l, b):
        return 2*(l + b)
		
class Rectangle(Area, Perimeter):
    def __init__(self, l, b):
        self.length = l
        self.breadth = b
	
    def area(self):
        return super().getArea(self.length, self.breadth)
	
    def perimeter(self):
        return super().getPerimeter(self.length, self.breadth)
		
rect = Rectangle(7, 4)

print("Area:", rect.area())
print("Perimeter:", rect.perimeter())
Output
Area: 28
Perimeter: 22

In this example, the class Rectangle inherits two classes Area and Perimeter. The class Area has a method getArea() which receives length and breadth and returns the area. The class Perimeter also has a method getPerimeter() which receives length and breadth and returns the perimeter.

When we created the object rect of the class Rectangle, its constructor got called and assigned the values 7 and 4 to the attributes length and breadth respectively for the object rect. So the length and breadth of rect became 7 and 4 respectively.

Then the object called the method area() of the class Rectangle which called the method getArea(l, b) of its parent class Area assigning the values 7 and 4 to the parameters l and b respectively.  This method then returned the area of the rectangle of length 7 and breadth 4.

Similarly, we returned the perimeter of the rectangle using the class Perimeter.

Note that in super().getArea(self.length, self.breadth), the getArea() method of the parent class Area got called, and in super().getPerimeter(self.length, self.breadth), the getPerimeter() method of the class Perimeter got called.

You were already aware of the concept of inheritance. In this chapter, we saw the different ways we can implement it.

When you want something, all the universe conspires in helping you to achieve it.
- Paulo Coelho


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