Is-A and Has-A relationships in python

 

In object-oriented programming, the concept of IS-A is a totally based on Inheritance, which can be of two types Class Inheritance or Interface Inheritance. It is just like saying "A is a B type of thing". For example, Apple is a Fruit, Car is a Vehicle etc. Inheritance is uni-directional. For example, House is a Building. But Building is not a House.

#Is-A relationship --> By Inheritance

class A:

  def __init__(self):

    self.b=10

  def mym1(self):

    print('Parent method')

class B(A):

  def mym2(self):

    print('Child method')

d = B()

d.mym1()

#output: Parent method

d.mym2()

#output: Child method

HAS-A Relationship: 

Composition(HAS-A) simply mean the use of instance variables that are references to other objects. For example Maruti has Engine, or House has Bathroom.

Let’s understand these concepts with an example of Car class.

# Has-A relationship --> By Composition

class Engine:

  def __init__(self):

    self.b = 20

  def myEngine(self):

    print('This is Engine class')

class Car:

  def __init__(self):

    self.engine = Engine()

  def mycar(self):

    print('Car use Engine class functionality')

    print(self.engine.b)

    self.engine.myEngine()

a = Car()

a.mycar()

Output:

Car use Engine class functionality 20 This is Engine class

A program to show differentiation between Is-A and Has-A

class Car:

  def __init__(self,name,colour):

    self.name = name

    self.colour = colour

  def Printinfo(self):

    print('car name is {},colour is {}'.format(self.name,self.colour))

class Person:

  def __init__(self,name,age):

    self.name = name

    self.age = age

  def breathe(self):

    print('breathing')

class Employee(Person):

  def __init__(self,name,age,empno,car):

    super().__init__(name,age)

    self.empno = empno

    self.car = car #Has-A

  def empinfo(self):

    print('name is {},age is {},empno is {}'.format(self.name,self.age,self.empno)) #is-A

  def empcarinfo(self):

    print('car details:')

    self.car.Printinfo()

c = Car('swift','red')

emp1 = Employee('tom',24,14356,c)

emp1.empinfo()

name is tom,age is 24,empno is 14356

emp1.empcarinfo()

car details: car name is swift,colour is red

emp1.breathe()

breathing