Regex,functions, inheritance,class, attribute,overloding

UNIT-IV
G. Venkata Kishore
Asst. Prof

Python- OOPs concept:
Class and object, Attributes,
Inheritance, Overloading Overriding,
Data hiding.
Regular Expressions: Match function,
Search function, Matching VS
Searching, Modifiers Patterns.

Object-oriented programming is one of
the most effective approaches to writing
soft ware.
In object-oriented programming you
write classes that represent real-world
things and situations, and you create
objects based on these classes.
When you write a class, you define the
general behavior that a whole category
of objects can have.

PROCEDURE ORIENTED
⦿The languages like C, Pascal, etc are called
Procedure Oriented Programming languages
since in these languages, a programmer uses
procedures or functions to perform a task.
⦿While developing a software, the main task is
divided into several sub tasks and each sub
task is represented as a procedure or
function.
⦿The main task is thus composed of several
procedures and functions. This approach is
called Procedure oriented approach.

Main()
function
Function 1
Function 2
Function 3
Sub task1
Sub task 2
Sub task3
PROCEDURE ORIENTED APPROACH

PROBLEMS IN PROCEDURE ORIENTED
APPROACH
⦿ No reusability of an existing code. A new task every time requires
developing the code from the scratch.
⦿ Functions may depend on other functions, this makes debugging
difficult.
⦿ Updating the software will also be difficult.
⦿ The program code is harder to write when Procedural
Programming is employed as the control on the code decreases
after certain point.

OBJECT ORIENTED
⦿ OOPs is a program paradigm based on the concept of
objects.
⦿ Languages like C++, Java and Python use classes and
objects in their program are called Object Oriented
programming languages.
⦿ A class is a module which itself contains data and
methods(functions) to achieve the task.
⦿ The main task is divided into several sub tasks, and
these are represented as classes.
⦿ Each class can perform several inter-related tasks
for which several methods are written in a class.
This approach is called Object Oriented approach.

Class with
main()
method
Class1 with data
and methods
Class1 with data
and methods
Class1 with data
and methods
Sub task1
Sub task 2
Sub task 3
main task
OBJECT ORIENTED APPROACH

SPECIALTY OF PYTHON LANGUAGE
⦿Though, Python is an object oriented
programming language like Java, it does not
force the programmers to write programs in
complete object oriented way.
⦿Unlike Java, Python has the blend of both the
object oriented and procedure oriented
features.
⦿Hence the programmer can write the program
as per their requirement.

FEATURES OF OOPS:
There are five important features related to
object oriented programming system. They are:
⦿Classes and Objects.
⦿Encapsulation.
⦿Abstraction.
⦿Inheritance.
⦿Polymorphism.

CLASSES AND OBJECTS
⦿ In python every thing is an object.
⦿ To create objects we require some Model or Plan or
Blue print, which is nothing but class.
⦿ We can write a class to represent properties
(attributes) and actions (behavior) of object.

ENCAPSULATION
⦿ Encapsulation is a mechanism where the data(variables) and
the code(methods) that act on the data will bind together. If
we take a class, we write the variables and methods inside the
class, Class is binding them together. Class is an example for
Encapsulation.
⦿ Eg: We can write a Student class with ‘id’ and ‘name’ as
attributes along with the display() method that displays this
data.
⦿ Eg: Capsule
ABSTRACTION
Hides unnecessary data from user and expose only essential
information is Abstraction.(hides unnecessary information)
Eg: Car, Toon App, AC.

INHERITANCE
⦿ Creating new classes from existing classes, so that
the new classes will acquire all the features of the
existing classes is called Inheritance.
⦿ E.g.: Parent Child.
POLYMORPHISM
⦿ Poly means ‘many’ and morphos means ‘forms’,
Polymorphism represents the ability to assume several
different forms.
⦿ If an object is exhibiting different behavior in different
contexts, it is called polymorphic nature.
⦿ Eg: Human

CLASSES AND OBJECTS
⦿ Class is a collection of objects. Class is a model or
blue print to create an object.
⦿ We write a class with attributes and actions of
objects.
⦿ Object is an instance of a class.
⦿ Properties can be represented by variables
⦿ Actions can be represented by Methods.
⦿ Hence class contains both variables and methods.
⦿ Physical existence of a class is nothing but object.
⦿ We can create any number of objects for a class.

CAR
COLOUR
PRICE
BRAND
OBJECT
ATTRIBUTE
S

CLASS OBJECTS
CAR SUV
KIA
CLASS OBJECTS
ANIMAL LION
LEOPARD
TIGER
⮚ Class is a blueprint which is used to create an object.
⮚ OBJECT IS AN INSTANCE OF A CLASS.

E.g.:
⦿ Every object has some behavior. The behavior of
an object is represented by attributes and actions.
⦿ Eg: A Person named ‘Joe’
⦿ Joe is an object because he exists physically. He
has attributes like name, age, gender etc.
⦿ These attributes can be represented by variables in
our programming.
⦿ Eg: ‘name’ is a string type variable,
⦿ ‘age’ is an integer type variable.

Name
Age
Gender
Talking
Walking
Eating
talk()
walk()
eat()
Joe
20
M
attributes
actions
attributes
methods
Class: Person Object: Joe

Person
Id
Name
Age
Sex
City
Ph no
Eat()
Walk()
Study()
Play()
Person 2/Emp 2:
Jessie
|
|
|
Person 3/Emp 3:
John
|
|
|
Person 1/Emp 1:
1
Joe
20
M
Hyd
123423
class
Attributes()
Methods()

CREATE A CLASS
⦿ A CLASS IS CREATED with the keyword class and then mention the
class name.
⦿ After the class name ‘object’ is written inside the class name.
⦿ class ClassName:
<statement-1>
.
.
<statement-N>
Eg: class class1():
pass
object1= class1()
object1.name = ‘Joe’

CREATE A CLASS WITH MULTIPLE OBJECTS

METHOD EXECUTION VS CONSTRUCTOR EXECUTION

THE SELF
VARIABLE:
⦿ ‘Self is a default variable that contains the memory
address of the instance of the current class. So, we
can use ‘Self’ to refer all the instance variables and
instance methods.
⦿ Eg: s1 =Student()
⦿ Here, s1 contains the memory address of the
instance. This memory address is internally and by
default passed to ‘Self’ variable. Since ‘Self’ knows
the memory address of the instance, it can refer to
all the members of the instance.
⦿ SELF CAN BE USED IN TWO WAYS
⦿ 1) def __init__(self):
⦿ 2) def talk(self):

CONSTRUCTOR
⦿Constructor is a special method used to initialize
the instance variables of a class.
⦿In constructor we create the instance variables
and initialize them with some starting values.
⦿The first parameter of the constructor will be
‘self’ variable that contains memory address of the
instance.
⦿Eg: def __init__(self):
⦿ self.name=‘Joe’
⦿ self.age = 20
⦿S1 = student()

CREATE A CLASS WITH CONSTRUCTOR

CLASS WITH A METHOD (FUNCTION)
EG: 1

CLASS WITH METHODS (FUNCTIONS)
EG: 2

CLASS WITH METHODS (FUNCTIONS)
Eg: 3

A python program to define student class and create an object to it. Also
calling the method and display the students details.

TYPES OF VARIABLES:
⦿The variables which are written inside a class
are of 2 types:
⦿Instance Variables
⦿Class variables or Static variables

INSTANCE VARIABLE
If we change anything in instance variables, it will
not effect to other objects.
We can declare Instance variables:
⦿1. Inside Constructor by using self variable
⦿2. Inside Instance Method by using self variable
⦿3. Outside of the class by using object reference
variable

1. INSIDE CONSTRUCTOR BY USING SELF VARIABLE
⦿We can declare instance variables inside a
constructor by using self keyword.
⦿Once we create object, automatically these
variables will be added to the object.

2. INSIDE INSTANCE METHOD BY USING SELF
VARIABLE:
⦿ We can also declare instance variables inside
instance method by using self variable.
⦿ If any instance variable declared inside instance
method, that instance variable will be added once
we call that method.

3. OUTSIDE OF THE CLASS BY USING OBJECT
REFERENCE VARIABLE:
⦿We can also add instance variables outside of a
class to a particular object.

EXAMPLE OF INSTANCE VARIABLE
Instance variables

STATIC VARIABLES:
⦿Class variables are the variables whose single
copy is available to all the instances of the
class. If we modify the copy of class variable in
an instance, it will modify all the copies in the
other instances.
⦿In general we can declare within the class
directly but from out side of any method.

EXAMPLE OF STATIC/CLASS VARIABLES
Static/ Class variable
To access the static
method we have to
use object name
dot(.) static
variable name

Another way to access the static variable

HOW TO MODIFY STATIC VARIABLE
⦿We can also modify or the change the static/
class variable.
⦿To modify the static variable we have to use
the class name dot (.) static variable name.

HOW TO DELETE STATIC VARIABLE
We can delete static variables from anywhere by using the
following syntax
del classname.variablename

TYPES OF METHODS
⦿The purpose of the method is to process the
variables provided in the class or in the method.
⦿Methods can be classified into the following 3
types:
⦿Instance Methods
⦿Class Methods
⦿Static Methods

CLASS METHODS
⦿Inside method implementation if we are using
only class variables(static variables),then such
type of methods we should declare as class
method.
⦿We can declare class method explicitly by using
@classmethod.
⦿By default, the first parameter for class is cls,
which refers to the class itself.

STATIC METHODS
⦿Static method are used when processing is
related to the class, but it does not include any
class or instances to perform any task.
⦿For Eg: counting the number of instances in the
class or changing the attributes in class.
⦿Static methods are written with @staticmethod

INHERITANCE
⦿ Inheritance is an important aspect of the object-oriented
paradigm.
⦿ Inheritance provides code reusability to the program
because we can use an existing class to create a new
class instead of creating it from scratch.
⦿ In inheritance, the child class acquires the properties
and can access all the data members and functions
defined in the parent class.
⦿ A child class can also provide its specific implementation
to the functions of the parent class.
⦿ In python, a derived class can inherit base class by just
mentioning the base in the bracket after the derived
class name.
⦿ Consider the following syntax to inherit a base class into
the derived class.

⦿ The relationship from person to a student is termed
‘Specialization’. Conversely, every student is a person, this is
called Generalization.
⦿ In this representation, we use an arrow towards the base class
as a UML (Unified Modeling Language) convention.
⦿ Here,
⦿ Parent can be called any of the following:
⦿ Super Class
⦿ Parent Class
⦿ Base Class
⦿ Likewise, Student here is:
⦿ Sub Class
⦿ Child Class
⦿ Derived Class
Parent
Student

1. SINGLE INHERITANCE:
⦿When a child class inherits from only one
parent class, it is called as single inheritance.
⦿
Base Class
Derived Class
Deriving one or sub classes from a single base class is
called single inheritance.

SINGLE INHERITANCE:
Without inheriting After inheriting

MULTI-LEVEL INHERITANCE
⦿ The multi-level inheritance includes the involvement
of at least two or more than two classes.
⦿ Multi-Level Inheritance is achieved when a derived
class inherits another derived class.
⦿ One class inherits the features from a parent class
and the newly created sub-class becomes the base
class for another new class.
Class -1
Class- 2
Class- N

MULTIPLE INHERITANCE
⦿ Multiple inheritances is where a subclass can inherit
features from more than one parent class.
⦿ In multiple inheritance the newly derived class can
have more than one superclass. And this newly
derived class can inherit the features from these
super classes it has inherited from, so there are no
restrictions.
BASE CLASS1 BASE CLASS 2 BASE CLASS 3
DERIVED
CLASS

POLYMORPHISM
⦿ Polymorphism is a word that came from two Greek
words, poly means many and morphos means forms.
If something exhibits various forms, it is called as
polymorphism.
⦿ Eg: Human, Wheat
⦿ In programming, a variable or an object or a method
will also exhibit the same nature.
⦿ A variable may store different types of data, an
object may exhibit different behaviors in different
contexts, or a method may perform various tasks.
⦿ The main examples for polymorphism in python are:
⦿ METHOD OVERLOADING
⦿ METHOD OVERRIDING

Eg:
⦿ An operator is a symbol that performs some action.
For eg: ‘+’ is an operator performs addition
operation when used on numbers, when an
operator can perform different actions, it is said
to exhibit polymorphism.

METHOD OVERLOADING
⦿If a method is written such that it can perform
more than one task, it is called method
overloading.
⦿We see method overloading in the languages like
Java.
⦿Method overloading is not available in Python,
writing more, We can achieve method overloading
by writing same method with several parameters.
⦿The method performs the operation depending on
the number of Arguments passed in the method
call.
⦿For eg: We can write sum() method with default
value ‘None’ for the arguments.

def sum(self, a=None, b=None, c=None):
if a!=None and b! =None and c!=None:
print(‘sum of three=‘, a+b+c)
elif a!=None and b!=None:
print(‘sum of two=‘, a+b)

METHOD OVERRIDING
⦿When there is a method in the super class,
writing the same method in the sub class so that
it replaces the super class method is called
‘method overriding’
⦿Base class will override the method in the super
class.
⦿Base class's method is called as the overridden
method and the derived class method is
called as overriding method.

DATA HIDING
⦿It is a method used in (OOP) to hide with the
information/ data.
⦿The object details such as data members, are
hidden within a class.
⦿We can restrict the data members to class to
maintain integrity.
⦿To hide any variable we have to use double
underscore __ prefix the variable name, then
such variables are not directly visible to the
outsiders.

REGULAR EXPRESSION:
⦿ A regular expression is a string that contains special
symbols and characters to find and extract the
information needed by us from the given data.
⦿ A regular expression helps us in search information,
match, find, and split information as per our
requirements.
⦿ A regular expression is also called as ‘Regex’
⦿ Python provides re module that stands for regular
expression. This module contains methods like
compile(), search(), match(), findall(), split()
⦿ When we write a regular expression we have to import
re module as
⦿ Import re

The regular expressions are used to perform the
following operations:
⦿Matching strings
⦿Searching for all strings
⦿Finding all strings
⦿Splitting a string into pieces
⦿Replacing strings.

The following methods belong to the ‘re’ module
that are used in the regular expression
⦿ The match() method searches the beginning of the
strings and if the matching string is found, it returns
the resultant string, otherwise it returns None. To
access the string from the returned value use group()
method.
⦿ The search() method searches the string from
beginning till the end and returns the first occurrence
of the matching string, otherwise it returns None.
We can use group() method to retrieve the string
from returned value.
⦿ To findall() method searches the string from
beginning till the end and returns all occurrences of
the matching string in the form of a list object. If the
matching strings are not found it returns empty list.
We can retrieve the resultant string pieces from the
list using a for loop.

⦿ The split() method splits the string according to
the regular expression and the resultant pieces are
returned as a list. If there are no string pieces,
then it returns an empty list. We can retrieve the
resultant string pieces from the list using a for
loop.
⦿ The sub() method substitutes(or replaces) new
strings in the place of existing strings.

Sequence characters in regular expressions
Pre-defined
Character
Description
d Represents any digit (0-9)
D Represents any non digit
s Represents white spaces(t, n)
S Represents non whitespaces
w Represents any aplhanumeric(A-Z, a-z,0-9)
W Represents any non aplhanumeric
b Represents a space around words
A Matches only at start of the string
z Matches only at end of the string

⦿ import re
#importing the regular expression module
⦿ prog =re.compile(r’mww’)
#prog represents an object that contains regular expression
⦿ str = ‘car mat bat rat’
#this is the string on which regular expression will act.
⦿ result = prog.search(str)
#searching the regular expression in the string
⦿ print(result.group)
#the result will store in ‘result’ object and we can display it
by calling the group() method.

A python program to create a regular expression to search for strings
starting with ‘c’ and having 3 characters using the SEARCH METHOD()

A python program to create a regular expression using the
MATCH METHOD() to search for strings starting with ‘m’ and having 3
characters.
A python program to create a regular expression using the
match method() to search for strings starting with ‘m’ and
having 4 characters.

A python program to create a regular expression to search for strings
starting with ‘m’ and having 3 characters using the findall() method

A PYTHON PROGRAM TO CREATE A REGULAR EXPRESSION TO
REPLACE A STRING WITH A NEW STRING

FULLMATCH()
⦿ We can use fullmatch() function to match a pattern to all of
target string. i.e. complete string should be matched
according to given pattern.
⦿ If complete string matched then this function returns Match
object otherwise it returns None.

MATCHING VERSUS SEARCHING
⦿ Python offers two different primitive operations based on
regular expressions: match checks for a match only at the
beginning of the string, while search checks for a match
anywhere in the string.
⦿ re.search() function will search the regular expression
pattern and return the first occurrence. Unlike Python
re.match(), it will check all lines of the input string. The
Python re.search() function returns a match object when
the pattern is found and “null” if the pattern is not found

Character classes
Character Description
[abc] Either a or b or c
[^abc] Except a and b and c
[a-z] Any lower case alphabet symbol
[A-Z] Any uppercase alphabet symbol
[a-zA-Z] Any alphabet symbol
[0-9] Any digit from 0 to 9
[a-zA-Z0-9] Any alphanumeric character
[^a-zA-Z0-9] Except alphanumeric character(special
characters)

A python program to create a regular expression to retrieve
all words starting with a given string
It returned ‘ay’ also, ay is not a word
it is a part of away. To avoid such
things use b before and after the
words in regular expression
b represents a space around words
w indicates any one
alphanumeric character.
Suppose if we write it as
[w]*, Here * represents 0
or more repetitions.
Hence [w]* represents 0
or more alphanumeric
characters.

a – any string starting with a
ba- any word starts with a
bab- matches only word a
Ba- any string that contains but does not begin with a

A python program to create a regular expression to retrieve all words
starting with a numeric digit
We want to retrieve all the words starting with a numeric
digit i.e 0,1 – 9. The numeric digit is represented by ‘d’
and hence, the expression is r’d[w]*

all words having 5 characters length.
all words having 3 characters length.

all words between 3 or 4 or 5 characters length.

QUANTIFIERS
Character Description
? Occurs 0 or 1 time
+ Occurs 1 or more than one time
* Occurs 0 or more times
{n} Occurs n no. of times
{n, } Occurs n or more than n times
{x,y} Occurs at least x times but less than y times

the phone number of a person.
d represents any digit(0-9)
+ indicates 1 or more times
the name of a person.
D represents any digit(0-9)
+ indicates 1 or more times

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