OOPS-PYTHON.pptx OOPS IN PYTHON APPLIED PROGRAMMING

Class and Objects
A class is a blueprint from which individual objects are created. An
object is a bundle of related state (variables) and behavior (methods).
Objects contain variables, which represents the state of information
about the thing you are trying to model, and the methods represent
the behavior or functionality that you want it to have

continued
Variables refers to both Instance variables and Class variables, unless
explicitly specified. Class objects are often used to model the real-world
objects that you find in everyday life. Objects are key to understanding object-
oriented technology. Look around right now and you’ll find many examples of
real-world objects: your dog, your desk, your television set, your bicycle. Real-
world objects share two characteristics: They all have state and behavior. Dogs
have state (name, color, breed, hungry) and behavior (barking, fetching,
wagging tail). Bicycles also have state (current gear, current pedal cadence,
current speed) and behavior (changing gear, changing pedal cadence, applying
brakes). Identifying the state and behavior for real-world objects is a great
way to begin thinking in terms of object-oriented programming

Creating Classes in Python
Related variables and methods are grouped together in classes. The
simplest form of class definition looks like this:
class ClassName:
<statement1>
-------
<statement>

continued
Classes are defined by using the class keyword, followed by the
ClassName and a colon. Class definitions must be executed before they
have any effect. In practice, the statements inside a class definition will
usually be function definitions, but few other statements are allowed.
Because these functions are indented under a class, they are called
methods. Methods are a special kind of function that is defined within
a class.
Python program to illustrate classes and object creation
Filename:c1.py,c2.py

Class mobile
Let’s define a class called Mobile that has two methods associated
with it one is receive_message() and another is send_message().
The first parameter in each of these methods is the word self. Self
is a default variable which contains the memory address of the
invoking object of the class. In the method definition, self doesn’t
need to be the only parameter and it can have multiple
parameters. Creating the Mobile class provided us with a blueprint
for an object. Just because you have defined a class doesn’t mean
you have created any Mobile objects. __init__ (self) is a special
method called as constructor. It is implicitly called when object of
the class is created

Creating Objects in Python
Object refers to a particular instance of a class where the object contains variables and
methods defined in the class. Class objects support two kinds of operations: attribute
references and instantiation. The act of creating an object from a class is called
instantiation. The names in a class are referenced by objects and are called attribute
references. There are two kinds of attribute references, data attributes and method
attributes. Variables defined within the methods are called instance variables and are used
to store data values. New instance variables are associated with each of the objects that
are created for a class. These instance variables are also called data attributes. Method
attributes are methods inside a class and are referenced by objects of a class. Attribute
references use the standard dot notation syntax as supported in Python.
• object_name.data_attribute_name
• object_name.method_attribute_name()
. The syntax for Class instantiation is,
• object_name = ClassName(argument_1, argument_2, ….., argument_n)
optional

The Constructor Method
Python uses a special method called a constructor method. Python
allows you to define only one constructor per class. Also known as the
__init__() method, it will be the first method definition of a class and its
syntax is,

continued
The __init__() method defines and initializes the instance variables. It is
invoked as soon as an object of a class is instantiated. The __init__()
method for a newly created object is automatically executed with all of
its parameters. The __init__() method is indeed a special method as
other methods do not receive this treatment. The parameters for
__init__() method are initialized with the arguments that you had
passed during instantiation of the class object. Class methods that
begin with a double underscore (__) are called special methods as they
have special meaning. The number of arguments during the
instantiation of the class object should be equivalent to the number of
parameters in __init__() method (excluding the self parameter).

Programs on classes
Python program to create a class Mobile with attributes name, price and model. Use
constructor to initialize the instance variable and display method to display the
details of a mobile
filename:c3.py
Python program to create a class Student with attributes name, sem division and
USN. Use to set() to initialize the attributes and get() method to display the details
of a student
Filename:c4.py
Write Python Program to Calculate the Arc Length of an Angle by Assigning Values to
the Radius and Angle Data Attributes of the class ArcLength
Filename:c5.py

Access specifiers
By default all members are public
Variable name or method name prefixed with single underscore(_) are treated
as protected member
self._name=‘raj’
def _display(self):
Variable name or method name prefixed with double underscore(__) are
treated as private member
self.__name=‘raj’
def __display(self):

continued
Write Python Program to Simulate a Bank Account with private data
attributes name and balance and protected methods depositMoney,
withdrawMoney and showBalance
filename:c6.py

Classes with Multiple Objects
Multiple objects for a class can be created while attaching a unique copy
of data attributes and methods of the class to each of these objects.
Define a class student with private data attributes name and marks.
Read n student details and print student details along with grade
obtained.
Filename c7.py
Write a python program to simulate bank operations using class concept
Filename:c8.py

Default parameters
Python program to illustrate default parameters
Filename:c9.py

Using Objects as Arguments
An object can be passed to a calling function as an argument
Python Program to Demonstrate Passing of an Object as an Argument
to a Function Call
filename:c10.py
Given Three Points (x1, y1), (x2, y2) and (x3, y3), Write a Python
Program to Check If they are Collinear using class concept
Filename:c11.py
Three points lie on the straight line if the area formed by the triangle of these three points is zero. So we will check if the area formed by the
triangle is zero or not
Formula for area of triangle is : 0.5 * [x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)]

Objects as Return Values
It is important to note that everything in Python is an object, including classes. In
Python, “everything is an object” (that is, all values are objects) because Python
does not include any primitive, unboxed values. Anything that can be used as a
value (int, str, float, functions, modules, etc.) is implemented as an object. The id()
function is used to find the identity of the location of the object in memory. The
syntax for id() function is
id(object)
This function returns the “identity” of an object. This is an integer (or long
integer), which is guaranteed to be unique and constant for this object during its
lifetime. Two objects with non-overlapping lifetimes may have the same id() value.

continued
You can check whether an object is an instance of a given class or not
by using the isinstance() function. The syntax for isinstance() function is,
isinstance (object, classinfo)
where the object is an object instance and classinfo can be a class, or a
tuple containing classes, or other tuples. The isinstance() function
returns a Boolean stating whether the object is an instance or subclass
of another object.

program
Given the Coordinates (x, y) of a Center of a Circle and Its Radius, Write
Python Program to Determine Whether the Point Lies Inside the Circle,
On the Circle or Outside the Circle using class Circle
Filename:c12.py
The idea is compute distance of point from center. If distance
is less than or equal to radius. the point is inside, else outside.
If((x-cir_x)*(x-cir_x)+(y-cir_y)*(y-cir_y)==r*r
Write Python Program to Compute the End Time, While Start Time and
Duration are Given using a class Time
Filename:c13.py

Class Attributes versus Data Attributes
Generally speaking, Data attributes are instance variables that are
unique to each object of a class, and Class attributes are class variables
that is shared by all objects of a class.
Program to Illustrate Class Variables and Instance Variables
Filename:c14.py

Encapsulation
Encapsulation is one of the fundamental concepts in object-oriented
programming (OOP). Encapsulation is the process of combining
variables that store data and methods that work on those variables into
a single unit called class. In Encapsulation, the variables are not
accessed directly. It is accessed through the methods present in the
class. Encapsulation ensures that the object’s internal representation
(its state and behavior) are hidden from the rest of the application.
Thus, encapsulation makes the concept of data hiding possible.
Given a point(x, y), Write Python Program to Find Whether it Lies in
the First, Second, Third or Fourth Quadrant of x - y Plane
filename:c15.py

Inheritance
Inheritance enables new classes to receive or inherit variables and
methods of existing classes. Inheritance is a way to express a relationship
between classes. If you want to build a new class, which is already similar
to one that already exists, then instead of creating a new class from
scratch you can reference the existing class and indicate what is different
by overriding some of its behavior or by adding some new functionality.
A class that is used as the basis for inheritance is called a superclass or
base class. A class that inherits from a base class is called a subclass or
derived class. The terms parent class and child class are also acceptable
terms to use respectively. A derived class inherits variables and methods
from its base class while adding additional variables and methods of its
own. Inheritance easily enables reusing of existing code.

Continued
The relationship between derived classes and base class using the
phrase is-a, then that relationship is inheritance. For example, a lemon
is-a citrus fruit, which is-a fruit. A shepherd is-a dog, which is-a animal.
A guitar is-a steel-stringed instrument, which is-a musical instrument. If
the is-a relationship does not exist between a derived class and base
class, you should not use inheritance.

The syntax for a derived class definition
To create a derived class, you add a
BaseClassName after theDerivedClassName
within the parenthesis followed by a colon.
The derived class is said to directly inherit
from the listed base class.

continued
In place of a base class name, other arbitrary expressions are also
allowed. This can be useful, for example, when the base class is defined
in another module:

program
Program to Demonstrate Base and Derived Class Relationship Without
Using __init__() Method in a Derived Class
Filename:c16.py

Using super() Function and Overriding Base
Class Methods
In a single inheritance, the built-in super() function can be used to refer to base classes without
naming them explicitly, thus making the code more maintainable. If you need to access the data
attributes from the base class in addition to the data attributes being specified in the derived class’s
__init__() method, then you must explicitly call the base class __init__() method using super()
yourself, since that will not happen automatically. However, if you do not need any data attributes
from the base class, then no need to use super() function to invoke base class __init__() method.
The syntax for using super() in derived class __init__() method definition looks like this:
super().__init__(base_class_parameter(s))
Its usage is shown below.
class DerivedClassName(BaseClassName):
def __init__(self, derived_class_parameter(s), base_class_parameter(s))
super().__init__(base_class_parameter(s))
self.derived_class_instance_variable = derived_class_parameter

program
Program to Demonstrate the Use of super() Function
filename:c17.py
Define derived class Enggstudent from a base class Student with private
attributes branch semester and division. Base class has private
members name and USN. Override display method in base and derived
class to display the details of a student
Filename:c18.py

Multiple Inheritances
Python also supports a form of multiple inheritances. A derived class definition with multiple base
classes looks like this:
class DerivedClassName(Base_1, Base_2, Base_3):
<statement-1>
. . .
<statement-N>
Derived class DerivedClassName is inherited from multiple base classes, Base_1, Base_2, Base_3.
For most purposes, in the simplest cases, you can think of the search for attributes inherited from a
parent class as depth-first, left-to-right, not searching twice in the same class where there is an
overlap in the hierarchy. Thus, if an attribute is not found in DerivedClassName, it is searched for in
Base_1, then (recursively) in the base classes of Base_1, and if it was not found there, it would be
searched for in Base_2, and so on. Even though multiple inheritances are available in Python
programming language, it is not highly encouraged to use it as it is hard and error prone. You can
call the base class method directly using Base Class name itself without using the super() function

Continued
The syntax is,
BaseClassName.methodname(self, arguments)
Notice the difference between super() function and the base class name in calling
the method name.
Use issubclass() function to check class inheritance. The syntax is,
issubclass(DerivedClassName, BaseClassName)
This function returns Boolean True if DerivedClassName is a derived class of base
class BaseClassName. The DerivedClassName class is considered a subclass of
itself. BaseClassName may be a tuple of classes, in which case every entry in
BaseClassName will be checked. In any other case, a TypeError exception is raised

Program on multiple inheritance
Python program to derive a new class movie from base class director
and actor.
Filename:c19.py
Program to Demonstrate Multiple Inheritance with Method Overriding
Filename:c20.py

Method resolution order
When method overriding is used in multiple inheritance always the
derived class invokes always its own class override method. To invoke
overrided methods in base class solution is method resolution order
What is MRO?
In python, method resolution order defines the order in
which the base classes are searched when executing a
method. First, the method or attribute is searched within a
class and then it follows the order we specified while
inheriting. This order is also called Linearization of a class and
set of rules are called MRO(Method Resolution Order).

continued
Methods for Method Resolution Order(MRO) of a class:
To get the method resolution order of a class we can use either
__mro__ attribute or mro() method. By using these methods we
can display the order in which methods are resolved.
Filename:c20.py

Diamond problem/Deadly Diamond of Death
Classes First, Second, Third, and Fourth are defined. Class Fourth
inherits from both Second and Third classes. Class Second and Third
inherit from class First. Hence class Fourth will have two copies of class
First and is called diamond problem of multiple inheritance
Program to illustrate diamond problem
Filename:c21,c22

The Polymorphism
Poly means many and morphism means forms. Polymorphism is one of
the tenets of Object Oriented Programming (OOP). Polymorphism
means that you can have multiple classes where each class implements
the same variables or methods in different ways. Polymorphism takes
advantage of inheritance in order to make this happen. A real-world
example of polymorphism is suppose when if you are in classroom that
time you behave like a student, when you are in market at that time
you behave like a customer, when you are at your home at that time
you behave like a son or daughter, such that same person is presented
as having different behaviors

Programs on polymorphism
Python program to illustrate polymorphism
Filename:c24.py
Write Python Program to Calculate Area and Perimeter of Different
Shapes Using Polymorphism
Filename:c25.py

Operator Overloading and Magic Methods
Operator Overloading is a specific case of polymorphism, where
different operators have different implementations depending on their
arguments. A class can implement certain operations that are invoked
by special syntax by defining methods with special names called “Magic
Methods”. This is Python’s approach to operator overloading

Python magic methods or special functions for operator overloading
Binary operators
operator Magic Method
+ __add__(self, other)
– __sub__(self, other)
* __mul__(self, other)
/ __truediv__(self, other)
// __floordiv__(self, other)
% __mod__(self, other)
** __pow__(self, other)
>> __rshift__(self, other)
<< __lshift__(self, other)
& __and__(self, other)
| __or__(self, other)
^ __xor__(self, other)

Comparison Operators :
< __LT__(SELF, OTHER)
> __GT__(SELF, OTHER)
<= __LE__(SELF, OTHER)
>= __GE__(SELF, OTHER)
== __EQ__(SELF, OTHER)
!= __NE__(SELF, OTHER)

Assignment Operators :
-= __ISUB__(SELF, OTHER)
+= __IADD__(SELF, OTHER)
*= __IMUL__(SELF, OTHER)
/= __IDIV__(SELF, OTHER)
//= __IFLOORDIV__(SELF, OTHER)
%= __IMOD__(SELF, OTHER)
**= __IPOW__(SELF, OTHER)
>>= __IRSHIFT__(SELF, OTHER)
<<= __ILSHIFT__(SELF, OTHER)
&= __IAND__(SELF, OTHER)
|= __IOR__(SELF, OTHER)
^= __IXOR__(SELF, OTHER)

Unary Operators :
– __NEG__(SELF, OTHER)
+ __POS__(SELF, OTHER)
~ __INVERT__(SELF, OTHER)

Program on operator overloading
Write Python Program to Create a Class Called as Complex and
Implement __add__() Method to Add Two Complex Numbers. Display
the Result by Overloading the + Operator
Filename:c26.py
Consider a Rectangle Class and Create Two Rectangle Objects. This
Program Should Check Whether the Area of the First Rectangle is
Greater than Second by Overloading > Operator
Filename:

OOPS-PYTHON.pptx OOPS IN PYTHON APPLIED PROGRAMMING

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