🔹 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

Here’s a simple explanation of Modules in Python with examples, definitions, and practice questions

🧠 What is a Module in Python?

• A module is a Python file (.py) that contains code, functions, or variables.
• You can import and use it in another file.
• Python has built-in modules and you can also create your own.

🔍 Why Use Modules?

• To reuse code.
• To organize code in separate files.
• To keep programs clean and simple.

✅ Types of Modules

✅ Importing a Module

👉 Syntax:

import module_name

🔹 Example:

import math
print(math.sqrt(16))  # Output: 4.0

✅ Using Specific Functions from a Module

from math import sqrt, pi
print(sqrt(25))       # Output: 5.0
print(pi)             # Output: 3.1415926535...

✅ Rename a Module (alias)

import math as m
print(m.pow(2, 3))  # Output: 8.0

✅ Creating Your Own Module

Step 1: Create a file called mymodule.py

# mymodule.py
def greet(name):
    print("Hello", name)

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

Step 2: Use it in another file:

# main.py
import mymodule

mymodule.greet("Ravi")
print(mymodule.add(5, 3))  # Output: 8

✅ Built-in Module Examples

🔹 math Module

import math
print(math.ceil(4.2))    # Output: 5
print(math.floor(4.7))   # Output: 4
print(math.factorial(5)) # Output: 120

🔹 random Module

import random
print(random.randint(1, 10))  # Random number from 1 to 10

🔹 datetime Module

import datetime
now = datetime.datetime.now()
print(now)  # Current date and time

📝 Practice Questions + Answers

❓ Q1: Import math module and print the square root of 81.

✅ Answer:

import math
print(math.sqrt(81))  # Output: 9.0

❓ Q2: Create your own module with a function that says “Welcome!” and call it.

✅ Answer:

File: mygreet.py

def welcome():
    print("Welcome to Python!")

File: main.py

import mygreet
mygreet.welcome()

❓ Q3: Use the random module to print a random number between 50 and 100.

✅ Answer:

import random
print(random.randint(50, 100))

❓ Q4: From math module, import only pow and sqrt.

✅ Answer:

from math import pow, sqrt
print(pow(2, 3))    # 8.0
print(sqrt(49))     # 7.0

❓ Q5: What is the benefit of using modules?

✅ Simple Answer:

• Reuse code
• Organize code
• Avoid writing the same code again

📌 Summary Table

Here’s a simple explanation of functions in Python in easy international English, perfect for students and beginners:

🧠 What is a Function?

• A function is a block of code that does a specific job.
• You can use it again and again.
• It helps make your program clean and easy.

🔧 Why Use Functions?

• Avoid writing the same code again.
• Break big problems into small parts.
• Makes your program organized.

✏️ How to Create a Function

✅ Syntax:

def function_name():
    # your code here

✅ Example:

def say_hello():
    print("Hello, students!")

▶️ How to Call a Function

say_hello()

✅ Function with Parameters

• You can send values into a function using parameters.

def greet(name):
    print("Hello", name)

Call it like:

greet("Alice")
greet("Ravi")

✅ Function with Return Value

• A function can give back (return) a value.

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

result = add(5, 3)
print("Sum is:", result)

🧊 Types of Functions in Python

🛠 Activity – Create and Use a Function

def multiply(x, y):
    result = x * y
    return result

num1 = int(input("Enter first number: "))
num2 = int(input("Enter second number: "))
print("Multiplication is:", multiply(num1, num2))

✅ Summary Table

Here are more examples, practice questions, and answers to help students understand Functions in Python better

✅ More Function Examples

🔹 Example 1: Function with No Parameters, No Return

def welcome():
    print("Welcome to Python class!")

welcome()

🔹 Example 2: Function with Parameters

def greet(name):
    print("Hello", name)

greet("Asha")
greet("John")

🔹 Example 3: Function with Return

def square(n):
    return n * n

result = square(4)
print("Square is:", result)

🔹 Example 4: Find Maximum of Two Numbers

def find_max(a, b):
    if a > b:
        return a
    else:
        return b

print("Max is:", find_max(10, 20))

🔹 Example 5: Even or Odd

def check_even_odd(n):
    if n % 2 == 0:
        return "Even"
    else:
        return "Odd"

print(check_even_odd(7))  # Output: Odd

🔹 Example 6: Factorial of a Number

def factorial(n):
    result = 1
    for i in range(1, n+1):
        result *= i
    return result

print("Factorial of 5 is:", factorial(5))  # 120

🔹 Example 7: Sum of a List

def sum_list(numbers):
    total = 0
    for n in numbers:
        total += n
    return total

print(sum_list([1, 2, 3, 4]))  # Output: 10

📝 Practice Questions + Answers

❓ Q1: Write a function that multiplies two numbers and returns the result.

✅ Answer:

def multiply(a, b):
    return a * b

print(multiply(3, 4))  # Output: 12

❓ Q2: Create a function that checks if a number is positive or negative.

✅ Answer:

def check_number(n):
    if n >= 0:
        return "Positive"
    else:
        return "Negative"

print(check_number(-5))  # Output: Negative

❓ Q3: Write a function that returns the length of a word.

✅ Answer:

def word_length(word):
    return len(word)

print(word_length("Python"))  # Output: 6

❓ Q4: Write a function that returns the reverse of a string.

✅ Answer:

def reverse_string(text):
    return text[::-1]

print(reverse_string("hello"))  # Output: olleh

❓ Q5: Write a function that returns the average of 3 numbers.

✅ Answer:

def average(a, b, c):
    return (a + b + c) / 3

print(average(10, 20, 30))  # Output: 20.0

📚 Challenge Practice

❓ Q6: Create a function that takes a list of numbers and returns only even numbers.

✅ Answer:

def get_even_numbers(numbers):
    evens = []
    for n in numbers:
        if n % 2 == 0:
            evens.append(n)
    return evens

print(get_even_numbers([1, 2, 3, 4, 5, 6]))  # Output: [2, 4, 6]

❓ Q7: Write a function that counts vowels in a string.

✅ Answer:

def count_vowels(text):
    vowels = 'aeiouAEIOU'
    count = 0
    for char in text:
        if char in vowels:
            count += 1
    return count

print(count_vowels("Python is easy"))  # Output: 4

✅ Summary