Python - Method Overriding

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You can always override your parent class methods. One reason for overriding parent's methods is that you may want special or different functionality in your subclass.

Example

class Parent: # define parent class
   def myMethod(self):
      print ('Calling parent method')

class Child(Parent): # define child class
   def myMethod(self):
      print ('Calling child method')

c = Child() # instance of child
c.myMethod() # child calls overridden method

When the above code is executed, it produces the following output −

Calling child method

To understand inheritance in Python, let us take another example. We use following Employee class as parent class −

class Employee:
   def __init__(self,nm, sal):
      self.name=nm
      self.salary=sal
   def getName(self):
      return self.name
   def getSalary(self):
      return self.salary

Next, we define a SalesOfficer class that uses Employee as parent class. It inherits the instance variables name and salary from the parent. Additionally, the child class has one more instance variable incentive.

We shall use built-in function super() that returns reference of the parent class and call the parent constructor within the child constructor __init__() method.

class SalesOfficer(Employee):
   def __init__(self,nm, sal, inc):
      super().__init__(nm,sal)
      self.incnt=inc
   def getSalary(self):
      return self.salary+self.incnt

The getSalary() method is overridden to add the incentive to salary.

Example

Declare the object of parent and child classes and see the effect of overriding. Complete code is below −

class Employee:
   def __init__(self,nm, sal):
      self.name=nm
      self.salary=sal
   def getName(self):
      return self.name
   def getSalary(self):
      return self.salary

class SalesOfficer(Employee):
   def __init__(self,nm, sal, inc):
      super().__init__(nm,sal)
      self.incnt=inc
   def getSalary(self):
      return self.salary+self.incnt

e1=Employee("Rajesh", 9000)
print ("Total salary for {} is Rs {}".format(e1.getName(),e1.getSalary()))
s1=SalesOfficer('Kiran', 10000, 1000)
print ("Total salary for {} is Rs {}".format(s1.getName(),s1.getSalary()))

When you execute this code, it will produce the following output −

Total salary for Rajesh is Rs 9000
Total salary for Kiran is Rs 11000

Base Overridable Methods

The following table lists some generic functionality of the object class, which is the parent class for all Python classes. You can override these methods in your own class −

Sr.No	Method, Description & Sample Call
1	__init__ ( self [,args...] ) Constructor (with any optional arguments) Sample Call : obj = className(args)
2	__del__( self ) Destructor, deletes an object Sample Call : del obj
3	__repr__( self ) Evaluatable string representation Sample Call : repr(obj)
4	__str__( self ) Printable string representation Sample Call : str(obj)