Instead of defining a class afresh, we 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 we 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.
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
#!/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
When the above code is executed, it produces the following result −
Calling child constructor Calling child method Calling parent method Parent attribute : 200