PYTHON INHERITANCE

Inheritance is a mechanism of object-oriented programming for deriving new classes (sub classes) from existing ones such as super class or base class. It allows us to define a class that inherits all the methods and properties from another class.

Parent class or base class, is the class being inherited from.

Child class or derived class, is the class that inherits from another class.

HOW TO CREATE A PARENT CLASS?

Any class can be a parent class.

Python Code

class Person:
  def __init__(self, Fname, Lname):
    self.Fname = Fname
    self.Lname = Lname
  def myfunction(self):
     print(self.Fname, self.Lname)
p1 = Person("John", "Doe")

p1.myfunction()

Output

John Doe

HOW TO CREATE A CHILD CLASS?

Creating Child Class

Child class inherit the properties of Parent Class it can be created by providing the parent class as a parameter when creating the child class as shown in following example, we are creating child class named as Employee which inherits the properties of parent class named as Person(refer to above example).

Python Code to create child class in Python

class Employee(Person):
  pass #Use the pass keyword for not adding new features

Adding the __init__() Function to Child Class

The __init__() function is called automatically every time the class is being used to create a new object.

When we add the __init__() function to the child class, the child class will no longer inherit the parent’s __init__() function. It will override the inheritance of the parent’s __init__() function.

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

class Person:
  def __init__(self, Fname, Lname):
    self.Fname = Fname
    self.Lname = Lname
  def myfunction(self):
     print(self.Fname, self.Lname)
class Employee(Person):
  def __init__(self, Fname, Lname):
     Person.__init__(self, Fname, Lname)
e1=Employee("Rakesh","Sharma")
e1.myfunction()

Output

Rakesh Sharma

Creating Child Class using the super() Function

super() Function

We can also use the super() function of Python that will make the child class inherit all the methods and properties from its parent. We need not to use the name of the parent class, it will automatically inherit the properties of the parent class.

Python code to use the super() function to create a child class

class Person:
  def __init__(self, Fname, Lname):
    self.Fname = Fname
    self.Lname = Lname
  def myfunction(self):
     print(self.Fname, self.Lname)
class Employee(Person):
  def __init__(self, Fname, Lname):
     super().__init__(Fname, Lname)
e1=Employee("Rakesh","Sharma")
e1.myfunction()

Output

Rakesh Sharma

Adding properties to child class

To add additional property we can add it in the __init__() function. The property named id is added below to the Employee class.

Python Code

class Person:
  def __init__(self, Fname, Lname):
    self.Fname = Fname
    self.Lname = Lname
  def myfunction(self):
     print(self.Fname, self.Lname)
class Employee(Person):
  def __init__(self, Fname, Lname):
     super().__init__(Fname, Lname)
     self.id=11
e1=Employee("Rakesh","Sharma")

print(e1.id)

Output

11

We can also add property to the child class as variable as shown In the example below, the id should be a variable, and passed into the Employee class when creating employee objects by adding another parameter in the __init__() function:

Python Code

class Person:
  def __init__(self, Fname, Lname):
    self.Fname = Fname
    self.Lname = Lname
  def myfunction(self):
     print(self.Fname, self.Lname)
class Employee(Person):
  def __init__(self, Fname, Lname, Eid):
     super().__init__(Fname, Lname)
     self.id=Eid
e1=Employee("Rakesh","Sharma",11)

print(e1.id)

Output

11

Adding methods to the child class

class Person:
  def __init__(self, Fname, Lname):
    self.Fname = Fname
    self.Lname = Lname
  def myfunction(self):
     print(self.Fname, self.Lname)
class Employee(Person):
  def __init__(self, Fname, Lname, Eid):
     super().__init__(Fname, Lname)
     self.id=Eid
  def warning(self):
     print("Access allowed to id -", self.id)
e1=Employee("Rakesh","Sharma",11)
e1.warning()

Output

Access allowed to id - 11

Note- Inheritance of parent method will be overridden on using the same name of method in child class as in the parent class.