Inheritance

Inheritance

Inheritance allows us to define new classes using classes that have already been defined.

Child classes inherits all the methods and properties from the parent class.

Parent class is also called as base class. Child class is also called derived class.

Any class can be a parent class, that is we can derive the child classes from any class.

Create a Child Class

To create a class that inherits the functionality from the parent class, we need to pass the parent class as a parameter while creating the child class.

Creating a child class from person class

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

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

class Student(Person):
  pass

x = Student("Bhavya", "Bindela")
x.printname()

Result:
Bhavya Bindela

In the above example, student class will have the same properties and methods as the person class.

__init__() function

As of now, Student class inherits the properties from the Person class. In order to add any properties to the Student class exclusively, we need to add init() function.

Defining __init__() function in the derived class

class Student(Person):
  def __init__(self, fname, lname):
      # we can add properties below

When you add the __init__() function, the child class will no longer inherit the parent's __init__() function.

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

Calling the parent's __init__() function

class Student(Person):
  def __init__(self, fname, lname):
    Person.__init__(self, fname, lname)

Super() function

Super() function in python allows the child class to inherit all the properties and methods from it's parent class.

Inherit the properties of parent class using super() function

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

Add properties in child class

As we are defining the initialize the function (constructor), we can add as many properties as needed.

Add properties

class Student(Person):
  def __init__(self, fname, lname):
    super().__init__(fname, lname)
    self.graduationyear = 2020

In the above example, as graduation year changes from student to student, we want to make the year (2019) as a variable and pass this as a parameter to the student class. Then

Adding parameters to the child class

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

  x = Student("Bhavya", "Bindela", 2020)
  print(x.graduationyear)

  Result:
  >> 2020

Add Methods in child class

We can add the methods in child class, just like we add methods in normal classes.

Adding methods

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)

x = Student("Bhavya", "Bindela", 2020)
x.welcome()

Reuslt:
>> Welcome Bhavya Bindela welcome to the class of 2020