Class Inheritance in Python

Instead of starting from scratch, you can create a class by deriving it from a preexisting class by listing the parent class in parentheses after the new class name.

The child class inherits the attributes of its parent class, and you can use those attributes as if they were defined in the child class. A child class can also override data members and methods from the parent.

Syntax

Derived classes are declared much like their parent class; however, a list of base classes to inherit from is given after the class name −

class SubClassName (ParentClass1[, ParentClass2, ...]):
'Optional class documentation string'
class_suite

Example

 Live Demo

#!/usr/bin/python
class Parent: # define parent class
   parentAttr = 100
   def __init__(self):
      print "Calling parent constructor"
   def parentMethod(self):
      print 'Calling parent method'
   def setAttr(self, attr):
      Parent.parentAttr = attr
   def getAttr(self):
      print "Parent attribute :", Parent.parentAttr
class Child(Parent): # define child class
   def __init__(self):
      print "Calling child constructor"
   def childMethod(self):
      print 'Calling child method'
c = Child()       # instance of child
c.childMethod()   # child calls its method
c.parentMethod()  # calls parent's method
c.setAttr(200)    # again call parent's method
c.getAttr()       # again call parent's method

Output

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

Calling child constructor
Calling child method
Calling parent method
Parent attribute : 200

Similar way, you can drive a class from multiple parent classes as follows −

class A: # define your class A
.....
class B: # define your class B
.....
class C(A, B): # subclass of A and B
.....

You can use issubclass() or isinstance() functions to check a relationships of two classes and instances.

• The issubclass(sub, sup) boolean function returns true if the given subclass sub is indeed a subclass of the superclass sup.
• The isinstance(obj, Class) boolean function returns true if obj is an instance of class Class or is an instance of a subclass of Class