Inheritance
Implementing Inheritance
Inheritance provides re-usability. With use of inheritance one class acquire the features of another class.
The existing class from where the class is inherited is called parent class or base class or super class. The class which inherits the child class is called the derived class or child class or sub class.
Example of inheritance:
Create a file vehicle.py:
class vehicle:
def setbrand(self,brand):
self.brand=brand
def getbrand(self):
return self.brand
Create a file fourwheeler.py:
from vehicle import vehicle
class fourwheeler(vehicle):
def setcapacity(self,capacity):
self.capacity=capacity
def getcapacity(self):
return self.capacity
car=fourwheeler()
car.setbrand("hundai")
car.setcapacity("1200cc")
print("The car brand is" + car.getbrand())
print("The car capacity is" +car.getcapacity())
Output:
The car brand ishundai
The car capacity is1200cc
Constructor in inheritance
The constructor of base class is by default available to sub class.
Example:
'''program of inheritance base class constructor from derived class'''
class base:
def __init__(self):
self.value=100
def display_val(self):
print("Value is", self.value)
class derived(base):
pass
d1=derived()
d1.display_val()
output:
('Value is', 100)
Overriding super class constructors and Methods
When method is written in sub class the super class method is not available in sub class. it is called method overriding. In constructor implicitly super keyword is used for default constructor in sub class to call default constructor of super class.
Example:
'''program of inheritance
constructor overriding
method overriding '''
class base:
def __init__(self):
self.value=100
def display_val(self):
self.value=5
print("Value is", self.value)
class derived(base):
def __init__(self):
self.value1=200
def display_val1(self):
print("Value1 is",self.value1)
d1=derived()
d1.display_val()
d1.display_val1()
Output:
('Value is', 5)
('Value1 is', 200)
Through above example we can identify that the default constructor is invoked automatically. If we make the derive class method name
display_val()
instead of
display_val1() then base class method can not be accessed. This is called method overriding.
Example:
class base:
def __init__(self):
self.value=100
def display_val(self):
self.value=5
print("Value is", self.value)
class derived(base):
def __init__(self):
self.value1=200
def display_val(self):
print("Value1 is",self.value1)
d1=derived()
d1.display_val()
#d1.display_val1()
Output:
Value1 is 200
The super method
In python super() is inbuilt method that is used to call the super class method or constructors.
To initialize the instance variable of super class through sub class super() method is used.
Syntax:
super().__init__()
The above syntax is used to call the super class default constructor.
super().__init__(parameters)
The above syntax is used to call the super class parameterized constructor. With use of above syntax value can be passed to the super class constructor from sub class constructor.
super().method()
The above syntax is used to call the super class methods.
'''program of inheritance
super constructor '''
class base:
def __init__(self,v):
self.value=v
def display_val(self):
print("Value is", self.value)
class derived(base):
def __init__(self,v,v1):
self.value1=v1
super().__init__(v)
def display_val1(self):
print("Value1 is",self.value1)
d1=derived(5,10)
d1.display_val()
d1.display_val1()
Output:
Value is 5
Value1 is 10
Example:
'''program of inheritance
super method '''
class base:
def __init__(self,v):
self.value=v
def display_val(self):
print("Value in base is ", self.value)
class derived(base):
def __init__(self,v,v1):
self.value1=v1
super().__init__(v)
def display_val(self):
print("Value in derived is",self.value1)
super().display_val()
d1=derived(5,10)
d1.display_val()
Output:
Value in derived is 10
Value in base is 5
