Python is also an object-oriented
language since its beginning. It allows us to develop applications using an
Object Oriented approach. In Python, we can easily create and use classes and
objects.
Major principles of
object-oriented programming system are given below.
- Object
- Class
- Method
- Inheritance
- Polymorphism
- Data
Abstraction
- Encapsulation
Object : The object is an
entity that has state and behavior. Everything in Python is an object, and
almost everything has attributes and methods.
Class : The class can be
defined as a collection of objects. It is a logical entity that has some
specific attributes and methods.
Example:
class Employee:
incremnt = 1.5
no_of_employee=0
def
__init__(self, fname, lname, salary):
self.fname = fname
self.lname = lname
self.salary = salary
Employee.no_of_employee += 1
def
increment(self):
print(self.incremnt)
print(Employee.incremnt)
self.salary = int(int(self.salary) * Employee.incremnt)
Method : The method is a
function that is associated with an object.
Example:
def increment(self):
self.salary = int(int(self.salary) * self.incremnt)
print(self.salary)
Inheritance : By using inheritance,
we can create a class which uses all the properties and behavior of another
class. The new class is known as a derived class or child class, and the one
whose properties are acquired is known as a base class or parent class.
It provides
re-usability of the code.
Example:
class Employee:
incremnt = 1.5
no_of_employee=0
def
__init__(self, fname, lname, salary):
self.fname = fname
self.lname = lname
self.salary = salary
#self.incremnt = 1.2
Employee.no_of_employee += 1
def
increment(self):
print(self.incremnt)
print(Employee.incremnt)
self.salary = int(int(self.salary) * Employee.incremnt)
@classmethod
def
change_increment(cls,amount):
cls.incremnt = amount
class
Programmer(Employee):
def
__init__(self,fname,lname,salary,proglang, exp):
super().__init__(fname,lname,salary)
self.proglang = proglang
self.exp = exp
def
increment(self):
self.salary = int(int(self.salary)*self.incremnt)
umesh =
Programmer('umesh','verma','45880','Python','8 years')
print(umesh.salary)
umesh.increment()
print(umesh.salary)
Polymorphism : Polymorphism
contains two words "poly" and "morphs". Poly means many and
Morphs means form, shape. By polymorphism, we understand that one task can be
performed in different ways.
Example:
class
India():
def capital(self):
print("New Delhi is the capital of
India.")
def language(self):
print("Hindi the primary language of
India.")
def type(self):
print("India is a developing country.")
class
USA():
def capital(self):
print("Washington, D.C. is the capital of
USA.")
def language(self):
print("English is the primary language of
USA.")
def type(self):
print("USA is a developed country.")
obj_ind =
India()
obj_usa =
USA()
for
country in (obj_ind, obj_usa):
country.capital()
country.language()
country.type()
Output:
New Delhi
is the capital of India.
Hindi the
primary language of India.
India is a
developing country.
Washington,
D.C. is the capital of USA.
English is
the primary language of USA.
USA is a
developed country.
Encapsulation : Encapsulation
is also an important aspect of object-oriented programming. It is used to
restrict access to methods and variables. In encapsulation, code and data are wrapped
together within a single unit from being modified by accident.
Note: The __init__ method
is a constructor and runs as soon as an object of a class is instantiated.
Public
members are those members of the class which can be accessed
outside the class environment.
Protected
members are those members of the class which cannot be
accessed outside the class but can be accessed from within the class and it’s
subclasses. To accomplish this in Python, just follow the convention by
prefixing the name of the member by a single underscore "_".
Private
members are similar to protected members, the difference is that the class
members declared private should neither be accessed outside the class nor by
any base class. In Python, there is no existence of Private instance variables
that cannot be accessed except inside a class. However, to define a private
member prefix the member name with double underscore "__".
Example :
class
Computer:
def __init__(self):
self.__maxprice = 900
def sell(self):
print("Selling Price: {}".format(self.__maxprice))
def setMaxPrice(self, price):
self.__maxprice = price
c =
Computer()
c.sell()
# change
the price
c.__maxprice
= 1000
c.sell()
# using
setter function
c.setMaxPrice(1000)
c.sell()
Output:
Selling
Price: 900
Selling
Price: 900
Selling
Price: 1000
Data
Abstraction : In python
by default, it is not able to provide abstract classes, but python comes up
with a module which provides the base for defining Abstract Base classes(ABC)
and that module name is ABC. ABC works by marking methods of the base class as
abstract and then registering concrete classes as implementations of the
abstract base. A method becomes an abstract by decorated it with a keyword
@abstractmethod.
For
Example:
# Python
program showing
# abstract
base class work
from abc
import ABC, abstractmethod
class
Polygon(ABC):
# abstract method
def noofsides(self):
pass
class
Triangle(Polygon):
# overriding abstract method
def noofsides(self):
print("I have 3 sides")
class
Pentagon(Polygon):
# overriding abstract method
def noofsides(self):
print("I have 5 sides")
class
Hexagon(Polygon):
# overriding abstract method
def noofsides(self):
print("I have 6 sides")
class
Quadrilateral(Polygon):
# overriding abstract method
def noofsides(self):
print("I have 4 sides")
# Driver
code
R =
Triangle()
R.noofsides()
K =
Quadrilateral()
K.noofsides()
R =
Pentagon()
R.noofsides()
K =
Hexagon()
K.noofsides()
Output:
I have 3
sides
I have 4
sides
I have 5
sides
I have 6
sides
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