Class and Object

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Introduction to Object-Oriented Programming (OOP)

Object-Oriented Programming (OOP) is a programming paradigm that models real-world problems using objects. Python supports both functional and object-oriented programming, but OOP is especially effective for building large, real-life, and scalable applications.

In OOP:

• Real-world entities are represented as objects
• Objects contain both data and behavior
• Programs become more structured, reusable, and easier to maintain

What Is a Class?

A class is a blueprint or template used to create objects.

It defines:

• Properties (attributes): Data or characteristics
• Behaviors (methods): Actions the object can perform

Example: A Computer class defines what a computer has (RAM, processor) and what it does (display configuration).

A single class can be used to create multiple objects, all sharing the same structure.

What Is an Object?

An object is a runtime instance of a class.

• Objects are created using the class name followed by parentheses
• Each object has its own identity and memory
• Objects can access class-defined methods and data

comp1 = Computer()
comp2 = Computer()

Here, comp1 and comp2 are two different objects created from the same class.

Creating a Class in Python

In Python, classes are defined using the class keyword.

class Computer:
    pass

• pass indicates an empty class
• Defining a class does not create an object

Instantiating an Object

To create an object:

• Use round brackets after the class name
• This process is called instantiation

comp1 = Computer()

❌ This does NOT create an object:

comp1 = Computer

It only assigns the class reference.

Objects and Types in Python

Python is fundamentally object-oriented.

Examples:

a = 10
print(type(a))        # <class 'int'>
print(type(comp1))    # <class '__main__.Computer'>

• Integers belong to the int class
• Custom objects belong to their defined class

Defining Methods in a Class

Methods are defined using def inside a class.

class Computer:
    def config(self):
        print("i7, 16GB, 1TB")

Calling Methods

Methods can be called in two ways:

Using the object (recommended):

com1 = Computer()
com1.config()

Using the class (explicitly passing the object):

Computer.config(com1)

In both cases:

The object is passed as self automatically when using object.method().

The Role of self

• self refers to the current object instance
• It allows methods to:
  • Access object data
  • Modify object attributes
• Enables multiple objects to share the same method logic while operating on different data

class Computer:
    def config(self):
        print("i7, 16GB, 1TB")

com1 = Computer()
com2 = Computer()

com1.config()
com2.config()

Both objects use the same method but remain independent.

Multiple Objects from One Class

• A single class can create multiple objects
• Each object:
  • Has its own memory location
  • Maintains independent state
• Methods are shared, data is separate

This is similar to:

• Multiple remotes controlling different devices
• Multiple humans sharing behaviors but having different identities

Summary

• A class is a blueprint while an object is its instance.
• Objects are created using constructor syntax ClassName().
• self represents the current object.
• Methods operate on object-specific data.
• Multiple objects share the same class but hold independent state.
• Python treats everything as an object at its core.