Introduction to Object Oriented Programming with Python 32022-07-19
Introduction to Object Oriented Programming with Python
Python supports both Procedural and Object Oriented approches in problem solving.
We can solve the complex problems with procedural approach but it makes difficulty in organizing and readability of the code. By using object oriented approach we can better organize the code and readability.
What is a class ?
Class is a set or category of things having some property or attribute in common and differentiated from others by kind, type, or quality. In technical terms we can say that class is a blue print for individual objects with exact behaviour.
What is object ?
object is one of instances of the class. which can perform the functionalities which are defined in the class.
In object oriented programming we have 4 basic concepts.
We can also have other terminology in OOP's
method overloading: By using method overloading we can use the parent Class method functionality and we can add extra functioanlity.
method overriding: By using method overriding we can replace the functionality of the parent Class method with our own functionality.
Let's take an example of a electric fan.
Data: Electric fan have four wings. It has color blue and it's a usha company fan. we can regulate(speed up or speed down) the speed of the fan. we can also swith-off and switch-on the fan.
Let's construct the class for Fan with above data
class Fan(object): # initialize the fan with basic data def __init__(self, company, color, number_of_wings): self.company = company self.color = color self.number_of_wings = number_of_wings def switch_on(self): print("fan started") def switch_off(self): print("fan stopped") def speed_up(self): print("speed increased by 1 unit") def speed_down(self): print("speed decreased by 1 unit")
How to get attributes and methods from data or our requirement/problem ?
First we have to analyze the problem. After analyzing the problem findout the verbs or required functionalities from our requirement/problem. These verbs or required functionalties will become methods to our class.
In above example we have below requirements
1. switch on the fan
2. switch off the fan
3. speed up the fan
4. speed down the fan
You can find that we have defined the same functionalities as methods to our class Fan.
Now, Find out the adjectives, nouns from the data these will become our attributes.
In above example we have the following attributes
1.company of fan
2.color of fan
3.number of wings of fan
How to create an object for a class ?
usha_fan = Fan( company="usha", color="blue", number_of_wings=3 )
We have created an object for class "Fan". Now, we can use the functionality of "Fan object". We can call the fan object as fan instance also.
# accessing attributes from an object >>> usha_fan Out: <__main__.Fan at 0x7f105819ff50> >>> usha_fan.company Out: 'usha' >>> usha_fan.color Out: 'blue' >>> usha_fan.number_of_wings Out: 3 # accessing methods from an object >>> usha_fan.switch_on() Out: fan started >>> usha_fan.switch_off() Out: fan stopped >>> usha_fan.speed_up() Out: speed increased by 1 unit >>> usha_fan.speed_down() Out: speed decreased by 1 unit
Lets consider the following scenario to understand the basic concepts of OOPS.
Human, Dogs, Cats, etc. belongs to the animal kingdom according to the biology. All of the animals have some common properties aswell as unique properties from one another.
Example for Inheritance and Polymorphism
class Animal(object): """ This is abstract class for Animal with common properties """ def __init__(self, name='Animal', no_of_legs): self.name = name self.no_of_legs = no_of_legs def kingdom(self): print("Animal Kingdom") # abstracted methods def talk(self): raise Exception("NotImplemented method") def eat(self): raise Exception("NotImplemented method") class Dog(Animal): def talk(self): print("Woof!") class Cat(Animal): def talk(self): print("Meow!") # Inheritance Example [Cat got the method kingdom from its parent Animal] >>> cat = Cat("Missy") >>> cat.kingdom() Out: Animal Kingdom # Polymorphism Exmple [same method work differently for different data types(Cat, Dog)] >>> cat = Cat("Missy") >>> c.talk() Out: Meow! >>> dog = Dog("Rocky") >>> dog.talk() Out: Woof!
Example for Encapsulation:
class Circle(object): pi = 3.141592 def __init__(self, radius=1): self.radius = radius def area(self): return self.radius * self.radius * Circle.pi def setRadius(self, radius): self.radius = radius def getRadius(self): return self.radius # encapsulation example >>> c = Circle() >>> c.setRadius(15) >>> c.area() Out: 47.1 # from above example we dont need to know the formula for calculating area of circle
In many applications/frameworks connecting to the database we just create the database like
database = new Database()
accually we don't know what's happening inside the method "connect"
It hides the implementation details[not required to know ] this is called encapsulation.