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Python OOP

Python is a multi-paradigm programming language. It supports different programming approaches.

One of the popular approaches to solve a programming problem is by creating objects. This is known as Object-Oriented Programming (OOP).

An object has two characteristics:

  • attributes
  • behavior

Let's take an example:

A parrot is an object, as it has the following properties:

  • name, age, color as attributes
  • singing, dancing as behavior

The concept of OOP in Python focuses on creating reusable code. This concept is also known as DRY (Don't Repeat Yourself).

In Python, the concept of OOP follows some basic principles:

Example

Object

Waiter

Attributes

is_holding_plate = True
tables_responsible = [4, 5, 6]

Methods (functions)

def take_order(table, order):
    #takes order to chef

def take_payment(amount):
    #add money to restaurant

Class

A class is a blueprint for the object.

We can think of class as a sketch of a parrot with labels. It contains all the details about the name, colors, size etc. Based on these descriptions, we can study about the parrot. Here, a parrot is an object.

The example for class of parrot can be :

class Parrot:
    pass

Here, we use the class keyword to define an empty class Parrot. From class, we construct instances. An instance is a specific object created from a particular class.

Object

An object (instance) is an instantiation of a class. When class is defined, only the description for the object is defined. Therefore, no memory or storage is allocated.

The example for object of parrot class can be:

obj = Parrot()

Here, obj is an object of class Parrot.

Suppose we have details of parrots. Now, we are going to show how to build the class and objects of parrots.

Example 1: Creating Class and Object in Python

class Parrot:

    # class attribute
    species = "bird"

    # instance attribute
    def __init__(self, name, age):
        self.name = name
        self.age = age

# instantiate the Parrot class
blu = Parrot("Blu", 10)
woo = Parrot("Woo", 15)

# access the class attributes
print("Blu is a {}".format(blu.__class__.species))
print("Woo is also a {}".format(woo.__class__.species))

# access the instance attributes
print("{} is {} years old".format( blu.name, blu.age))
print("{} is {} years old".format( woo.name, woo.age))

Output

Blu is a bird
Woo is also a bird
Blu is 10 years old
Woo is 15 years old

In the above program, we created a class with the name Parrot. Then, we define attributes. The attributes are a characteristic of an object.

These attributes are defined inside the __init__ method of the class. It is the initializer method that is first run as soon as the object is created.

Then, we create instances of the Parrot class. Here, blu and woo are references (value) to our new objects.

We can access the class attribute using __class__.species. Class attributes are the same for all instances of a class. Similarly, we access the instance attributes using blu.name and blu.age. However, instance attributes are different for every instance of a class.

Example 2

class Car:
	def __init__(self, seats):
	self.seats = seats


# 5 is set to define number of seats
my_car = Car(5)

# my_car=Car(5) can also be defined as
my_car.seats=5

Methods

Methods are functions defined inside the body of a class. They are used to define the behaviors of an object.

Example 1 : Creating Methods in Python

class Parrot:
    
    # instance attributes
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    # instance method
    def sing(self, song):
        return "{} sings {}".format(self.name, song)

    def dance(self):
        return "{} is now dancing".format(self.name)

# instantiate the object
blu = Parrot("Blu", 10)

# call our instance methods
print(blu.sing("'Happy'"))
print(blu.dance())

Output

Blu sings 'Happy'
Blu is now dancing

In the above program, we define two methods i.e sing() and dance(). These are called instance methods because they are called on an instance object i.e blu.

Example 2

class Car:
	def enter_race_mode():
		self.seats = 2

# Call method
my_car.enter_race_mode()

Key Points to Remember:

  • Object-Oriented Programming makes the program easy to understand as well as efficient.
  • Since the class is sharable, the code can be reused.
  • Data is safe and secure with data abstraction.
  • Polymorphism allows the same interface for different objects, so programmers can write efficient code.

References

YouTube