What is Python?

Python is a high-level, beginner-friendly programming language. It is used for web development, automation, data science, artificial intelligence, software development, scripting, and education.

Install Python on Windows

1. Go to the official Python website.
2. Download the latest Python version.
3. Run the installer.
4. Very important: tick Add Python to PATH.
5. Click Install Now.
6. Open Command Prompt and type:

python --version
pip --version

Install Code Editor

Recommended editor: Visual Studio Code. Install Python extension inside VS Code.

First Python Program

print("Hello, Python!")

Output:

Hello, Python!

Why Learn Python?

Python Program Structure

# This is a simple program
name = "Anu"
print("Welcome", name)

Interactive Mode vs Script Mode

Python Syntax

Python uses indentation to define code blocks. Other languages often use braces { }, but Python uses spaces.

if 10 > 5:
    print("10 is greater than 5")

Comments

# Single line comment

"""
Multi-line comment style
commonly used as documentation
"""

Variables

A variable is a name used to store data.

student_name = "Ravi"
age = 21
marks = 78.5
is_passed = True

Variable Naming Rules

• Can contain letters, numbers, and underscores.
• Cannot start with a number.
• Cannot use spaces.
• Names are case-sensitive.

Data type means the kind of value stored in a variable.

Check Type

x = 25
print(type(x))

Type Conversion

a = "10"
b = int(a)
print(b + 5)

Arithmetic Operators

Comparison Operators

x = 10
print(x == 10)
print(x != 5)
print(x > 3)

Logical Operators

age = 20
has_id = True

if age >= 18 and has_id:
    print("Allowed")

if, elif, else

marks = 75

if marks >= 75:
    print("A Grade")
elif marks >= 65:
    print("B Grade")
elif marks >= 50:
    print("C Grade")
else:
    print("Fail")

for Loop

for i in range(1, 6):
    print(i)

while Loop

count = 1

while count <= 5:
    print(count)
    count += 1

break and continue

for i in range(1, 10):
    if i == 5:
        break
    print(i)

A string is a sequence of characters.

message = "Welcome to Python"
print(message)

String Indexing

text = "Python"
print(text[0])   # P
print(text[-1])  # n

String Slicing

text = "Python Programming"
print(text[0:6])
print(text[7:])

Useful String Methods

name = "  python course  "
print(name.upper())
print(name.lower())
print(name.strip())
print(name.replace("python", "Java"))

f-string Formatting

name = "Arun"
age = 22
print(f"My name is {name} and I am {age} years old.")

List

A list is ordered and changeable.

fruits = ["apple", "banana", "mango"]
fruits.append("orange")
print(fruits)

Tuple

A tuple is ordered but unchangeable.

days = ("Monday", "Tuesday", "Wednesday")
print(days[0])

Set

A set stores unique values.

numbers = {1, 2, 2, 3}
print(numbers)

Dictionary

A dictionary stores data in key-value pairs.

student = {
    "name": "Kavi",
    "age": 20,
    "course": "Python"
}

print(student["name"])

A function is a reusable block of code.

Creating a Function

def greet():
    print("Hello!")

greet()

Function with Parameter

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

greet("Nimal")

Function with Return Value

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

result = add(10, 20)
print(result)

Default Parameter

def welcome(name="Student"):
    print("Welcome", name)

welcome()
welcome("Rani")

File handling is used to read and write files.

Write File

file = open("notes.txt", "w")
file.write("This is my Python note.")
file.close()

Read File

file = open("notes.txt", "r")
content = file.read()
print(content)
file.close()

Recommended Method: with

with open("notes.txt", "r") as file:
    content = file.read()
    print(content)

Error handling prevents a program from stopping suddenly.

try and except

try:
    number = int(input("Enter number: "))
    print(10 / number)
except:
    print("Something went wrong.")

Specific Exception

try:
    number = int(input("Enter number: "))
    print(10 / number)
except ValueError:
    print("Please enter only numbers.")
except ZeroDivisionError:
    print("Cannot divide by zero.")

finally

try:
    file = open("data.txt", "r")
    print(file.read())
except FileNotFoundError:
    print("File not found.")
finally:
    print("Program completed.")

OOP is a programming style based on classes and objects.

Class and Object

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

student1 = Student("Ravi", 21)
print(student1.name)
print(student1.age)

Method

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

    def say_hello(self):
        print("Hello, I am", self.name)

s1 = Student("Meena")
s1.say_hello()

Inheritance

class Animal:
    def sound(self):
        print("Animal makes sound")

class Dog(Animal):
    def bark(self):
        print("Dog barks")

d = Dog()
d.sound()
d.bark()

Important OOP Terms

Module

A module is a Python file that contains reusable code.

import math

print(math.sqrt(25))
print(math.pi)

Install Packages with pip

pip install requests

Using a Package

import requests

response = requests.get("https://example.com")
print(response.status_code)

Virtual Environment

A virtual environment keeps project packages separate.

python -m venv myenv

Activate on Windows:

myenv\Scripts\activate

Activate on macOS/Linux:

source myenv/bin/activate

Project 1: Student Grade System

name = input("Enter student name: ")
marks = float(input("Enter marks: "))

if marks >= 75:
    grade = "A"
elif marks >= 65:
    grade = "B"
elif marks >= 50:
    grade = "C"
else:
    grade = "Fail"

print("Student:", name)
print("Grade:", grade)

Project 2: Simple Login System

correct_username = "admin"
correct_password = "1234"

username = input("Username: ")
password = input("Password: ")

if username == correct_username and password == correct_password:
    print("Login successful")
else:
    print("Invalid username or password")

Project 3: To-Do List

tasks = []

while True:
    print("\n1. Add Task")
    print("2. View Tasks")
    print("3. Exit")

    choice = input("Choose: ")

    if choice == "1":
        task = input("Enter task: ")
        tasks.append(task)
        print("Task added.")
    elif choice == "2":
        for index, task in enumerate(tasks, start=1):
            print(index, task)
    elif choice == "3":
        break
    else:
        print("Invalid choice")

Project 4: Contact Book

contacts = {}

while True:
    print("\n1. Add Contact")
    print("2. Search Contact")
    print("3. Exit")

    choice = input("Choose: ")

    if choice == "1":
        name = input("Name: ")
        phone = input("Phone: ")
        contacts[name] = phone
        print("Contact saved.")
    elif choice == "2":
        name = input("Enter name to search: ")
        if name in contacts:
            print("Phone:", contacts[name])
        else:
            print("Contact not found.")
    elif choice == "3":
        break
    else:
        print("Invalid choice")