Object Oriented Programming in Python

Object-Oriented Programming (OOP) is a significant programming paradigm in programming languages. In Python, everything is an object. For code reusability, OOP is unparalleled. In this context, a class is the fundamental structural unit.

Class

A class acts as a blueprint for an object. Just like a mold in a brick kiln that is used to create numerous bricks of the same shape, in programming, a class can be used to create numerous objects of the same structure. Let’s see how to create a class in Python.

# This is an example of a class in Python
class TestClass:
    name="Python"
    
classObject=TestClass() # creating an object

print(classObject.name) # Accessing a class variable

Output:

Python 

Here, a class named TestClass is created. The structure of a class begins with the class keyword followed by the class name and a colon, with the class elements written within the indented block. In this example, a single variable name is used.

In line 5, an object of the class is created. Here, classObject is an object of TestClass.

In line 7, the name variable is accessed using the object. In Python, the dot operator (.) is used to access class variables.

Instance of a Class

The previous program was quite basic and had no practical application. Let’s delve a bit deeper with an example:

# This is an example of a class in Python
class MathClass:
    def __init__(self,x,y):
        self.x=x
        self.y=y
    def Multiply_function(self):
        z=self.x*self.y
        return z
    
firstObject=MathClass(5,10) # creating an object
secondObject=MathClass(2,4) # creating an object

print(firstObject.Multiply_function()) # Accessing a class function
print(secondObject.Multiply_function()) # Accessing a class function

Output:

50                                                                                                         
8

In line 2, a class named MathClass is defined. In line 6, a function named Multiply_function is declared which uses the self parameter. The self keyword is used to refer to the same class.

__init__ Function

Now the question is, what is the __init__ function and why is it used? The __init__ function is a default function in every class. It is primarily used to initialize an object. When an object is created, this function is called first and an instance is created, known as an instance of the class. It is also called a constructor.

In the above program, two objects are initialized in lines 10 and 11. Notice that two values are passed inside the class, and these values initialize the class.

In both cases, the same variables x and y are used, but the values for each object are different. Thus, the class acts as a mold, and different objects are created from it. To understand this better, consider the following example:

Output:

5
2

It is clear here that while the class variable (mold) is the same, the elements vary according to the object (product).

Modifying an Object Property

An object’s property can be modified in the same way, using the dot operator. For example:

# This is an example of a class in Python
class MathClass:
    def __init__(self,x,y):
        self.x=x
        self.y=y
    def Multiply_function(self):
        z=self.x*self.y
        return z
    
firstObject=MathClass(5,10) # creating an object

print(firstObject.Multiply_function()) # Accessing a class function

firstObject.x=15 #Modifying the class property

print(firstObject.Multiply_function()) # Accessing a class function after modifying the class property

Result:

50                                                                                                                            
150 

In lines 12 and 16, the function is called normally, but due to the change in value at line 14, the result is different.

Deleting an Object Property

To delete an object property, the del keyword is used. Here’s an example:

# This is an example of a class in Python
class MathClass:
    def __init__(self,x,y):
        self.x=x
        self.y=y
    def Multiply_function(self):
        z=self.x*self.y
        return z
    
firstObject=MathClass(5,10) # creating an object

print(firstObject.x) # Accessing a class property

del firstObject.x # Delete the class property

print(firstObject.x) # Accessing a class property after modifying the class property

Result:

5                                                                                                                             
Traceback (most recent call last):                                                                                            
  File "main.py", line 24, in <module>                                                                                        
    print(firstObject.x) # Accessing a class function after modifying the class property                                      
AttributeError: 'MathClass' object has no attribute 'x'

From the result, we see that 5 is printed before deleting the property. After the deletion, trying to access the property results in an AttributeError, indicating that the property no longer exists.

Deleting an Object

So far, we’ve seen how to delete properties. Now let’s see how to delete an entire object:

# This is an example of a class in Python
class MathClass:
    def __init__(self,x,y):
        self.x=x
        self.y=y
    def Multiply_function(self):
        z=self.x*self.y
        return z
    
firstObject=MathClass(5,10) # creating an object

print(firstObject.x) # Accessing a class function

del firstObject # Deleting the class

print(firstObject.x) # Accessing a class variable after deleting the class property

Result:

5                                                                                                                             
Traceback (most recent call last):                                                                                            
  File "main.py", line 24, in <module>                                                                                        
    print(firstObject.x) # Accessing a class variable after deleting the class property                                       
NameError: name 'FirstObject' is not defined

The result shows 5 before deleting the object. After deletion, trying to access the object results in a NameError, indicating that the object no longer exists.