🐍 Python Class – Full Explanation with Key Concepts

📘 What is a Python Class?

A class in Python is a blueprint for creating objects. It allows grouping of data (attributes) and behavior (methods) together to model real-world entities.

Think of a class as a design template. Objects are created based on this template, each with their own values.

🎯 Why Use Classes?

Encapsulate data and logic together.
Promotes code reuse through inheritance.
Helps organize and structure large applications.
Makes code modular, maintainable, and scalable.

🔑 Key Concepts of Python Classes

Concept	Description	Real-Time Example
`Class`	Blueprint for an object	`class Car:`
`Object`	Instance of a class	`my_car = Car()`
`__init__()`	Constructor method	Initialize attributes
`self`	Refers to current object	Used in all methods
`Attribute`	Variable stored in object	`self.name`
`Method`	Function inside a class	`def greet(self):`
`Inheritance`	Use code from another class	`class Manager(Employee):`
`Encapsulation`	Hide internal details	`_salary`, `__bonus`
`Polymorphism`	Same method, different behavior	`calculate_salary()` overridden

✅ Basic Python Class Example

class Employee:
    def __init__(self, name, role):
        self.name = name
        self.role = role

    def greet(self):
        return f"Hello, I am {self.name} and I work as a {self.role}"

# Creating object
emp = Employee("Sairam", "Data Engineer")
print(emp.greet())

Output:
Hello, I am Sairam and I work as a Data Engineer

🔁 Real-Time Scenario

Imagine building an employee management system. Each employee has a name, salary, and department. We want to give them raises and access info:

class Employee:
    def __init__(self, name, salary, dept):
        self.name = name
        self.salary = salary
        self.dept = dept

    def apply_raise(self, percent):
        self.salary += self.salary * (percent / 100)
        return self.salary

# Example usage
e1 = Employee("John", 50000, "IT")
print(e1.apply_raise(10))  # New salary: 55000

🧠 Summary of Class Features

Feature	Explanation
`__init__()`	Constructor for setting up data
`self`	Represents current object
Methods	Functions defined inside class
Object	Created instance of class
Inheritance	Child class can use Parent class methods
Encapsulation	Hide data inside private variables
Polymorphism	Reuse method name with different behavior

import boto3
import pandas as pd
import io

class S3ToS3:

    def __init__(self, aws_access_key_id, aws_secret_access_key, region_name,
                 source_bucket, source_key, destination_bucket, destination_key):

        self.aws_access_key_id = aws_access_key_id
        self.aws_secret_access_key = aws_secret_access_key
        self.region_name = region_name
        self.source_bucket = source_bucket
        self.source_key = source_key
        self.destination_bucket = destination_bucket
        self.destination_key = destination_key

        self.s3_client = boto3.client('s3',
                                 aws_access_key_id=self.aws_access_key_id,
                                 aws_secret_access_key=self.aws_secret_access_key,
                                 region_name=self.region_name)
        self.df = None


    def read_data_from_s3(self):
        response = self.s3_client.get_object(Bucket=self.source_bucket, Key=self.source_key)
        content = response['Body'].read().decode('utf-8')
        self.df = pd.read_csv(io.StringIO(content))

    def tranform_data(self):
        self.df = self.df[['employee_id', 'name']]

    def load_to_s3(self):
        csv_buffer = io.StringIO()
        self.df.to_csv(csv_buffer, index=False)
        self.s3_client.put_object(Bucket=self.destination_bucket, Key=self.destination_key, Body=csv_buffer.getvalue())


if __name__ == '__main__':

    obj = S3ToS3(aws_access_key_id, aws_secret_access_key, region_name, source_bucket,
                  source_key, destination_bucket, destination_key)

    print(obj.source_key)
    obj.read_data_from_s3()
    obj.tranform_data()
    obj.load_to_s3()