Overriding in Python
Method overriding is an ability of any object-oriented programming language that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes. When a method in a subclass has the same name, same parameters or signature and same return type(or sub-type) as a method in its super-class, then the method in the subclass is said to override the method in the super-class.
The version of a method that is executed will be determined by the object that is used to invoke it. If an object of a parent class is used to invoke the method, then the version in the parent class will be executed, but if an object of the subclass is used to invoke the method, then the version in the child class will be executed. In other words, it is the type of the object being referred to (not the type of the reference variable) that determines which version of an overridden method will be executed.
Example:
class Parent():
#
Constructor
def __init__(self):
self.value
= "Inside Parent"
#
Parent's show method
def show(self):
print(self.value)
# Defining child class
class Child(Parent):
#
Constructor
def __init__(self):
self.value
= "Inside Child"
#
Child's show method
def show(self):
print(self.value)
# Driver's code
obj1 = Parent()
obj2 = Child()
obj1.show()
obj2.show()
Output:
Inside Parent
Inside Child
Method overriding with multiple and multilevel inheritance
Multiple Inheritance: When
a class is derived from more than one base class it is called multiple Inheritance.
Example: Let’s consider an example where we want to override a method of one parent class only. Below is the implementation.
|
# Python program to
demonstrate # overriding in
multiple inheritance # Defining parent
class 1 class Parent1():
#
Parent's show method def show(self):
print("Inside
Parent1") # Defining Parent
class 2 class Parent2():
#
Parent's show method def display(self):
print("Inside
Parent2") # Defining child
class class Child(Parent1,
Parent2): #
Child's show method def show(self):
print("Inside
Child") # Driver's code obj = Child()
obj.show() obj.display() |
Output:
Inside Child
Inside Parent2
Using Super(): Python super() function
provides us the facility to
refer to the parent class explicitly. It is basically useful where we have to
call superclass functions. It returns the proxy object that allows us to refer
parent class by ‘super’.
Example 1:
|
class Parent():
def show(self):
print("Inside
Parent") class Child(Parent):
def show(self):
#
Calling the parent's class #
method super().show()
print("Inside
Child") # Driver's code obj = Child()
obj.show() |
Output:
Inside Parent
Inside Child
PYTHON OVERLOADING:
Like other languages (for example method overloading in C++)
do, python does not supports method overloading by default. But there are
different ways to achieve method overloading in Python.
The problem with method overloading in Python is that we may overload the methods but can only use the latest defined method.
# First product
method.
# Takes two argument
and print their
# product
def product(a, b):
p
= a * b
print(p)
# Second product
method
# Takes three argument
and print their
# product
def product(a, b, c):
p
= a * b*c
print(p)
# Uncommenting the
below line shows an error
product(4, 5)
product(4,5,6)
BY EXECUTING THIS WILL RAISE AN ERROR SINCE THE LATEST DEFINED FUCNTION IS TAKEN WITH THREE
ARGUMENTS.
What looks like overloading methods, it is actually that Python keeps only the latest definition of a method you declare to it. This code doesn’t make a call to the version of add() that takes in two arguments to add. So we find it safe to say Python doesn’t support method overloading. However, we recently ran into a rather Pythonic way to make this happen. Check this out:
1.
def add(instanceOf,*args):
2.
if instanceOf=='int':
3.
result=0
4.
if instanceOf=='str':
5.
result=''
6.
for i in args:
7.
result+=i
8.
return result
by using *args overloading can be solved
such as
In this code, not only do we use the *args magic variable for variable arity, we also let the code deal with both integers and strings. Watch it happen:
>>> add('int',3,4,5)
12
>>> add('str','I ','speak ','Python')
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