Chapter 07 inheritance

CHAPTER - 07
EXTENDING CLASSES - INHERITANCE

Unit I
Programming and Computational
Thinking (PCT-2)
(80 Theory + 70 Practical)
DCSc & Engg, PGDCA,ADCA,MCA.MSc(IT),Mtech(IT),MPhil (Comp. Sci)
Department of Computer Science, Sainik School Amaravathinagar
Cell No: 9431453730
Praveen M Jigajinni
Prepared by
Courtesy CBSE
Class XII

INHERITANCE
In object oriented programming,
inheritance is a mechanism in which a new
class is derived from an already defined
class. The derived class is known as a
subclass or a child class. The pre-existing
class is known as base class or a parent class
or a super class. The mechanism of
inheritance gives rise to hierarchy in classes.
The major purpose of inheriting a base class
into one or more derived class is code reuse.

INHERITANCE - OVERRIDING
What is Overriding?
The subclass inherits all the methods
and properties of the super class. The
subclass can also create its own methods
and replace methods of the superclass. The
process of replacing methods defined in
super with new methods with same name in
the derived class is known as overriding.

TYPES OF INHERITANCE
Inheritance can be categorised into five types:
1. SINGLE INHERITANCE
2. MULTILEVEL INHERITANCE
3. MULTIPLE INHERITANCE
4. HIERARCHICAL INHERITANCE
5. HYBRID INHERITANCE

1. SINGLE INHERITANCE
This is the simplest kind of inheritance.
In this, a subclass is derived from a single
base class.
BASE
DERIVED

2. MULTILEVEL INHERITANCE
In this type of inheritance, the derived
class becomes the base of another class.
BASE 1
DERIVED
BASE 2

3. MULTIPLE INHERITANCE
BASE 1
DERIVED
BASE 2
In this type of inheritance, the derived
class inherits from one or more base classes.

4. HIERARCHICAL INHERITANCE
In this type of inheritance, the base
class is inherited by more than one class.
BASE 1
DERIVED 2DERIVED 1

5. HYBRID INHERITANCE
This inheritance is a combination of multiple,
hierarchical and multilevel inheritance.
BASE 1
BASE 2
DERIVED 2DERIVED 1

EXAMPLES ON INHERITANCE
Syntax:
class subclass (super):
For Example
class person:
def __init__(self,name,age):
self.name=name
self.age=age
def getName(self):
return self.name

def getAge(self):
return self.Age
class student(person):
def __init__(self,name,age,rollno,marks):
super(student,self)._init_(self, name, age)
self.rollno=rollno
self.marks=marks
def getRoll(self):
return self.rollno
def getMarks(self):
return self.Marks

The above example implements single
inheritance. The class student extends the class
person. The class student adds two instance
variables rollno and marks. In order to add new
instance variables, the _init_() method defined
in class person needs to be extended.
The __init__() function of subclass student
initializesname and age attributes of superclass
person and also create new attributes rollno and
marks.

EXTENDING __init__ () METHOD
In python the above task of extending
__init__ () can be achieved the following ways:
i) By using super() function
ii) By using name of the super class.

super() FUNCTION
In the above example, the class student
and class person both have __init__ () method.
The __init__ () method is defined in cIass
person and extended in class student. In
Python, super() function is used to call the
methods of base class which have been
extended in derived class
Syntax:
super(type, variable) bound object

super() FUNCTION EXAMPLE
super(student, self).__init__ (self, name, age)
self.rollno=rollno
self.marks=marks

BY USING NAME OF THE SUPER CLASS

As discussed above, the class student and
class person both have __init__ () method. The
__init__ () method is defined in cIass person and
extended in class student. In Python, name of
the base class can also be used to access the
method of the base class which has been
extended in derived class.

Example
person.__init__ (self, name, age)
self.rollno=rollno
self.marks=marks

MULTIPLE INHERITANCE EXAMPLE
Python supports a limited form of multiple
inheritance as well. A class definition with
multiple base classes looks like this
class SubClassName( Base1, Base2, Base3):
<statement1>
.
.
.
<statement N>

For old-style classes, the only rule is
depth-first, left-to-right. Thus, if an attribute is
not found in SubClassName, it is searched in
Base1, then (recursively) in the base classes of
Base1, and only if it is not found there, it is
searched in Base2, and so on

For Example:
class student(object):
def __init__(self,Id,name):
self.Id=Id
self.name=name
def getName(self):
return self.name
def getId(self):
return self.Id
def show(self):
print self.name

print self.Id
class Teacher():
def __init__(self,tec_Id,tec_name, subject):
self.tec_Id=tec_Id
self.tec_name=tec_name
self.subject=subject
def getName(self):
return self.tec_name
def getId(self):
return self.tec_Id

def getSubject(self):
return self.ubject
def show(self):
print self. tec_name
print self.tec_Id
print self.subject
class school(student,Teacher):
def __init__(self, ID, name, tec_Id, tec_name, subject, sch_Id):
student.__init__ (self,ID,name)
Teacher. __init__(self,tec_Id,tec_name, subject)
self.sch_Id= sch_Id

def getId(self ):
return self.sch_Id
def display(self):
return self.sch_Id
In above example class school inherits class
student and teacher.
Let us consider these outputs
>>> s1=school(3,"Sham",56,"Ram","FIT",530)
>>> s1.display()
530

>>> s1.getId()
530
>>> s1.show()
Sham
3
The object of class school takes six
instance variables. The first five instance
variables have been defined in the base classes
(school and Teacher). The sixth instance
variable is defined in class school.

s1.display()displays the sch_Id and s1.getId()
also returns the sch_id. The classes school and
Teacher both have the method show (). But as
shown in above, the objects1 of class school
access the method of class student. This
because of depth-first, left-to-right rule.
Also, method getId()of class school is
overriding the methods with same names in
the base classes.

The feature of overriding methods
enables the programmer to provide specific
implementation to a method in the subclass
which is already implemented in the superclass.
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.
OVERRIDING METHODS

Example 1:
super(student,self).__init__(self, name,
age)
self.rollno=rollno
self.marks=marks
def getRoll(self):
return self.rollno
def getMarks(self):
return self.Marks
OVERRIDING METHODS

def show(self):
print self.rollno
print self.marks
As shown in the above example class
student inherits class person. Both the classes
have a function show( ).
The function show() in student is
overriding function show() in person().
OVERRIDING METHODS

The object of class person will print name
and age. The object of class student will print
rollno and marks. In case it is required that
function show of class student should display
name, age, rollno and marks, we should make
the following change in class student
super(student,self).__init__(self,name,age)
OVERRIDING METHODS

self.rollno=rollno
self.marks=marks
def getRoll(self):
return self.rollno
def getMarks(self):
return self.Marks
def show(self):
person.show( )
print self.rollno
print self.marks
OVERRIDING METHODS

CLASS TEST
1. What is inheritance?
2. What are the types of inheritance?
3. Explain Multiple Inheritance with suitable
example
4. What is super? Explain
5. Explain Overriding functions
Class : XII Time: 40 Min
Topic: Inheritance Max Marks: 20

Chapter 07 inheritance

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