🔹 What is self in Python?

• self means this object.
• It helps Python know which object we are talking about.
• It is used inside class functions to access the object’s data and functions.

📌 Important Points:

• self is not a keyword. You can name it anything (but using self is the rule).
• It is sent automatically when you call a function using an object.

🔹 Example 1: Using self to store data

class Student:
    def __init__(self, name, age):
        self.name = name  # save name
        self.age = age    # save age

    def show(self):
        print("Name:", self.name)
        print("Age:", self.age)

s1 = Student("Arun", 18)
s1.show()

✅ Output:

Name: Arun
Age: 18

🔹 How self works:

Let’s understand:

• self.name = name → store the value in the object.
• self.age = age → same for age.
• Later, inside the show() function, we again use self.name to get the data back.

🔹 Example 2: Use self in multiple objects

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

    def start(self):
        print(self.brand, "is starting...")

c1 = Car("Toyota")
c2 = Car("BMW")

c1.start()  # Toyota is starting...
c2.start()  # BMW is starting...

👉 Here, self.brand is different for each object.

🔹 Example 3: Change values using self

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

    def change_salary(self, new_salary):
        self.salary = new_salary

    def show(self):
        print("Name:", self.name)
        print("Salary:", self.salary)

e1 = Employee("Ravi", 30000)
e1.change_salary(40000)
e1.show()

✅ Output:

Name: Ravi
Salary: 40000

📝 Practice Questions with Answers

❓ Q1: Create a class Laptop with brand and price. Use self to store and print data.

✅ Answer:

class Laptop:
    def __init__(self, brand, price):
        self.brand = brand
        self.price = price

    def show(self):
        print("Brand:", self.brand)
        print("Price:", self.price)

l1 = Laptop("HP", 55000)
l1.show()

❓ Q2: Create a class Circle with radius. Use a method to calculate area. (Area = 3.14 × radius × radius)

✅ Answer:

class Circle:
    def __init__(self, radius):
        self.radius = radius

    def area(self):
        return 3.14 * self.radius * self.radius

c = Circle(5)
print("Area:", c.area())

🧾 Summary Table

📣 Next:

➡️ “Encapsulation in Python | Easy OOP Explanation for Beginners”

🔹 What is __init__()?

• __init__() is a special function in a class.
• It is called automatically when you create an object.
• It is used to give values to the object’s variables.

📌 We also call it a constructor.

🔹 Simple Example:

class Person:
    def __init__(self, name):
        self.name = name

p1 = Person("John")
print(p1.name)  # Output: John

🧾 What happens here?

1. We created a class called Person.
2. Inside the class, we wrote a __init__() function.
3. self.name = name means we are saving the name in the object.
4. We made an object p1 = Person("John"). It runs the __init__() and stores "John" inside it.

🔹 What is self in __init__()?

• self means this object.
• Python sends it automatically to every function inside a class.

class Student:
    def __init__(self, name, age):
        self.name = name
        self.age = age

s1 = Student("Arun", 18)
print(s1.name)  # Arun
print(s1.age)   # 18

🔹 You Can Add More Than One Parameter

class Car:
    def __init__(self, brand, year):
        self.brand = brand
        self.year = year

c1 = Car("Toyota", 2020)
print(c1.brand)  # Toyota
print(c1.year)   # 2020

📝 Practice Questions with Answers

❓ Q1: Create a class Book with title and author. Use __init__() to set values and print them.

✅ Answer:

class Book:
    def __init__(self, title, author):
        self.title = title
        self.author = author

b1 = Book("Python Basics", "Ravi")
print("Title:", b1.title)
print("Author:", b1.author)

❓ Q2: Create a class Laptop with brand and price. Use __init__() and print details.

✅ Answer:

class Laptop:
    def __init__(self, brand, price):
        self.brand = brand
        self.price = price

lap1 = Laptop("Dell", 50000)
print("Brand:", lap1.brand)
print("Price:", lap1.price)

🔎 Summary

📣 Coming Next:

➡️ “What is self in Python? | Easy Explanation with Examples”

🔹 What is a Class?

• A class is a template or design to make things (objects).
• It tells Python what the object has (variables) and what it can do (functions).

✅ Example:

class Student:
    def __init__(self, name, age):
        self.name = name
        self.age = age

This class is like a student form. It has:

• name
• age

🔹 What is an Object?

• An object is something real made from the class.
• We can make many objects from one class.

✅ Example:

s1 = Student("Arun", 18)
print(s1.name)  # Output: Arun

➡️ s1 is an object of the class Student.

🔹 __init__() Method

• This is a special function in the class.
• It runs automatically when you make an object.
• It gives values to the object.

✅ Example:

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

c1 = Car("Toyota")
print(c1.brand)  # Output: Toyota

🔹 What is self?

• self means this object.
• It is used to store data inside the object.

✅ Example:

class Example:
    def show(self):
        print("Hello from", self)

obj = Example()
obj.show()

🧠 Real-Life Example

Let’s say we want to make details of books.

✅ Example:

class Book:
    def __init__(self, title, author):
        self.title = title
        self.author = author

b1 = Book("Python Basics", "Ravi")
print(b1.title)   # Python Basics
print(b1.author)  # Ravi

✅ Benefits of Using Class and Object

📝 Practice Questions

Q1. Create a class Employee with name and salary. Show details.

✅ Answer:

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

    def show(self):
        print("Name:", self.name)
        print("Salary:", self.salary)

e1 = Employee("Meena", 25000)
e1.show()

🧾 Summary Table

🔗 Next Topic:

➡️ __init__() in Python – Constructor Made Simple (Coming up next)

🧩 What is __init__.py in Python?

📘 Definition

• __init__.py is a special Python file used to mark a folder as a Python package.
• It tells Python: “This folder contains Python code you can import.“

📦 Where is it used?

It is placed inside a package folder like this:

mypackage/
├── __init__.py
├── add.py
├── sub.py

✅ Why __init__.py is Important

✅ Example 1: Simple Empty __init__.py

# __init__.py
# (can be empty)

Usage:

from mypackage import add
print(add.add(2, 3))  # Output: 5

✅ Example 2: With Code in __init__.py

# __init__.py
print("Welcome to mypackage!")

def greet():
    print("Hello from the package!")

Usage:

import mypackage

mypackage.greet()

🖨 Output:

Welcome to mypackage!
Hello from the package!

✅ Example 3: Control Imports

If you want only certain modules to be accessible:

# __init__.py
__all__ = ['add']

Now:

from mypackage import *
# Only add is available, not sub

🔁 Summary

📝 Practice Task

❓ Create a package with:

• __init__.py (prints “Package loaded”)
• calc.py (function to add numbers)
• Then import and use it.

✅ Answer:

Folder: tools/

➡️ __init__.py

print("Package loaded!")

➡️ calc.py

def add(a, b):
    return a + b

➡️ Main file:

from tools import calc
print(calc.add(4, 5))  # Output: 9

Here’s a simple explanation of Libraries and Packages in Python — with examples, usage, and practice questions

📚 What is a Library in Python?

• A library is a collection of useful code (functions, classes, modules).
• It helps you do things quickly, without writing code from scratch.
• Python has many libraries for math, data, web, AI, etc.

🔹 Examples of Libraries:

📦 What is a Package?

• A package is a folder that contains modules (Python files) and a special file called __init__.py.
• Packages help to organize libraries better.
• You can think of:
  • Library = a toolset
  • Package = toolbox with organized tools (modules)

✅ Example: Using a Library

1. Math Library:

import math
print(math.pi)         # 3.1415...
print(math.sqrt(25))   # 5.0

2. Random Library:

import random
print(random.randint(1, 10))  # Random number between 1 and 10

✅ Using an External Library

• Some libraries are not built-in. You need to install them using pip:

pip install pandas

Then use it:

import pandas as pd
data = pd.Series([1, 2, 3])
print(data)

✅ Example: Package Structure

Imagine this folder:

mypackage/
    __init__.py
    add.py
    sub.py

add.py

def add(x, y):
    return x + y

sub.py

def sub(x, y):
    return x - y

Use the Package:

from mypackage import add, sub
print(add.add(3, 2))
print(sub.sub(5, 2))

📝 Practice Questions + Answers

❓ Q1: What is the difference between a module and a library?

✅ Answer:

• A module is one Python file (.py) with code.
• A library is a collection of modules.
• A package is a folder containing modules.

❓ Q2: Use the random library to generate a number between 100 and 200.

✅ Code:

import random
print(random.randint(100, 200))

❓ Q3: Install and use the numpy library to create a number array.

✅ Code:

pip install numpy

✅ Python:

import numpy as np
arr = np.array([10, 20, 30])
print(arr)

❓ Q4: What is the role of __init__.py in a package?

✅ Answer:

• It tells Python that the folder is a package.
• It can be empty or contain startup code.

❓ Q5: Create your own library with a function to find the square of a number.

✅ Create mylib.py:

def square(n):
    return n * n

✅ Use it:

import mylib
print(mylib.square(6))  # Output: 36

🔄 Summary Table