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Python Inheritance

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Python Inheritance

Table Of Contents:

  1. What Is Inheritance?
  2. Advantages Of Inheritance?
  3. Implementing Inheritance.
  4. Adding The __init__() Method In Child Class.
  5. Use Of super() Method.
  6. Adding Properties To Child Class.
  7. Adding Methods To Child Class.

(1) What Is Inheritance?

  • Inheritance enables one class to use all the properties and methods from another class, without writing any extra code in the child class.
  • The class from which you are deriving properties and behaviours is called Base Class.
  • The class which is using the properties and behaviours of another class is called Child Class.
  • This is how you inherit all the properties from your parents.

(2) Advantages Of Inheritance?

  • You can have code reusability through inheritance.
  • You don’t have to write the same code again and again.
  • It also allows for the addition of more features to the class without modifying it.
  • It can represent the real-world relationship between objects.
  • It is transitive in nature, which means that if class B inherits from another class A, then all the subclasses of B would automatically inherit from class A.

(3) Implementing Inheritance?

  • For implementing inheritance, you need to have a parent class from where you are going to inherit properties.
  • In the child class, you need to use the parent class name inside the parenthesis( ), after the child class name.

Example:

Creating Parent Class:

class Car:
    def __init__(self,name,color,price):
        self.name = name
        self.color = color
        self.price = price

Creating Child Class:

class BMW(Car):
    def car_details(self):
        print('Car Name:',self.name)
        print('Car Color:',self.color)
        print('Car Price:',self.price)

Creating Object Of Child Class:

bmw = BMW('BMW','Black',5000000)

bmw.car_details()
Output:
Car Name: BMW
Car Color: Black
Car Price: 5000000

Note:

  • Here you can see that I have inherited the Car class into the BMW class.
  • Hence, I can able to access the Car class properties.

(4)Adding The __init__() Method In Child Class.

  • When you add the __init__() function in the child class, the child class will no longer inherit the parent’s __init__() function.
  • The child’s __init__() function overrides the inheritance of the parent’s __init__() function.

Example

Creating Parent Class:

class Games:
    def __init__(self,name,players,famous_player):
        self.name = name
        self.players = players
        self.famous_player = famous_player
    def games_details(self):
        print('Game Name:',self.name)
        print('Game Players:',self.players)
        print('Game Famous Player:',self.famous_player)

Creating Child Class:

class Cricket(Games):
    def __init__(self,overs,team1,team2):
        self.overs = overs
        self.team1 = team1
        self.team2 = team2
    def match_details(self):
        print('Total Overs:',self.overs)
        print('Team 1:',self.team1)
        print('Team 2:',self.team2)

Creating Object Of Child Class:

match = Cricket('Cricket',11,'Sachin')

match.games_details()
Output:
AttributeError                            Traceback (most recent call last)
Input In [23], in <cell line: 1>()
----> 1 match.games_details()

Input In [11], in Games.games_details(self)
      6 def games_details(self):
----> 7     print('Game Name:',self.name)
      8     print('Game Players:',self.players)
      9     print('Game Famous Player:',self.famous_player)

AttributeError: 'Cricket' object has no attribute 'name'

Note:

  • As you have declared __init__() method inside the child class, you are not able to access the parent class variables.

(5) Solution To The __init__() Method In Child Class.

  • To keep the inheritance of the parent’s __init__() function, add a call to the parent’s __init__() function.

Example

Creating Parent Class:

class Games:
    def __init__(self,name,players,famous_player):
        self.name = name
        self.players = players
        self.famous_player = famous_player
    def games_details(self):
        print('Game Name:',self.name)
        print('Game Players:',self.players)
        print('Game Famous Player:',self.famous_player)

Creating Child Class:

class Cricket(Games):
    def __init__(self,name,players,famous_player):
        Games.__init__(self,name,players,famous_player)

Creating Object Of Child Class:

match = Cricket('Cricket',11,'Sachin')

match.games_details()
Output:
Game Name: Cricket
Game Players: 11
Game Famous Player: Sachin

Note:

  • Here you can see that we are able to access the parent class variables.

(6) Use Of Super Method.

  • super( ) the function makes the child class inherit all the methods and properties from its parent.
  • By using the super( ) function, you do not have to use the name of the parent element, it will automatically inherit the methods and properties from its parent.

Example

Creating Parent Class:

class Games:
    def __init__(self,name,players,famous_player):
        self.name = name
        self.players = players
        self.famous_player = famous_player
    def games_details(self):
        print('Game Name:',self.name)
        print('Game Players:',self.players)
        print('Game Famous Player:',self.famous_player)

Creating Child Class:

class Cricket(Games):
    def __init__(self,name,players,famous_player):
        super().__init__(name,players,famous_player) #Removed "self" keyword from here.

Creating Object Of Child Class:

match = Cricket('Cricket',11,'Kohli')

match.games_details()
Output:
Game Name: Cricket
Game Players: 11
Game Famous Player: Kohli

(7) Adding Properties To Child Class

  • You can also add a new property to the child class.
  • Let us see with an example.

Example

Creating Parent Class:

class Person:
    def __init__(self, fname, lname):
        self.firstname = fname
        self.lastname = lname

    def printname(self):
        print(self.firstname, self.lastname)

Creating Child Class:

class Student(Person):
    def __init__(self, fname, lname, year):
        super().__init__(fname, lname)
        self.graduationyear = year

Creating Object Of Child Class:

std = Student("Abhispa", "Pattnaik", 2022)

print(std.graduationyear)
Output:
2022

Note:

  • Here you can see that, I have added a new parameter ‘year’ to the __init__( ) method of the child class.

(8) Adding Methods To Child Class

  • You can also add a new method to the child class.
  • Let us see with an example.

Example

Creating Parent Class:

class Person:
    def __init__(self, fname, lname):
        self.firstname = fname
        self.lastname = lname

    def printname(self):
        print(self.firstname, self.lastname)

Creating Child Class:

class Student(Person):
    def __init__(self, fname, lname, year):
        super().__init__(fname, lname)
        self.graduationyear = year

    def welcome(self):
        print("Welcome", self.firstname, self.lastname, "To The Class Of", self.graduationyear)

Creating Object Of Child Class:

std = Student("Abhispa", "Pattnaik", 2022)

std.welcome()
Output:
Welcome Abhispa Pattnaik To The Class Of 2022

Note:

  • Here you can see that I have added a new method ‘welcome’ to the child class.

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