Introduction to Python

Python is a powerful and easy-to-learn programming language used for web development, automation, data science, artificial intelligence, and more.

It is beginner-friendly and widely used by professionals to build real-world applications.

Why Learn Python?

Steps to Run Your First Python Program

Example

print("Hello, World!")
    

Where Python is Used

• Web Development
• Automation & Scripting
• Game Development
• Data Science & AI
• Desktop Applications

Important Concepts

• Python is an interpreted language
• No need to compile code
• Indentation is important

Tips

• Practice daily
• Start with small programs
• Focus on logic building

Common Mistakes

• Ignoring indentation ❌
• Copy-paste without understanding ❌
• Not practicing enough ❌

Install Python & Setup

To start programming in Python, you first need to install it on your computer and set up a proper development environment.

This section will guide you step-by-step to install Python and configure your system correctly.

System Requirements

Steps to Install Python

Verify Installation

After installation, check if Python is installed correctly:

python --version
    

If installed properly, it will display the Python version.

Install Code Editor (VS Code)

Steps to Run Python in VS Code

Example

print("Python is installed successfully!")
    

Important Concepts

• PATH allows Python to run from any folder
• .py files are Python program files
• Interpreter runs Python code line by line

Tips

• Always install latest Python version
• Use VS Code for better experience
• Keep your setup clean and organized

Common Mistakes

• Not adding Python to PATH ❌
• Installing wrong version ❌
• Forgetting to install extension in VS Code ❌

First Python Program

Writing your first program is the beginning of your journey in Python. It helps you understand how code works and how output is displayed.

The most common first program is the Hello World program.

Basic Syntax of Python Program

Steps to Write First Program

Example

print("Hello, World!")
    

Output

Hello, World!
    

More Examples

print("Welcome to Python")
print("My name is Mohit")
print(10 + 5)
    

When to Use print()

• Displaying messages to user
• Showing output of calculations
• Debugging code

Important Concepts

• Python executes code line by line
• Each print() statement runs separately
• No semicolon required at end

Tips

• Always use correct spelling: print
• Use quotes for text
• Run code frequently to test

Common Mistakes

• Using Print instead of print ❌
• Forgetting quotes ❌
• Missing parentheses ❌

Python Syntax

Python Syntax refers to the set of rules that define how Python programs are written and executed. It is simple, clean, and easy to understand compared to other programming languages.

Learning syntax is important because even a small mistake can cause errors in your program.

Basic Syntax Rules

Indentation Example

if 5 > 2:
    print("5 is greater than 2")
    

Indentation is mandatory in Python. Without proper indentation, code will give an error.

Case Sensitivity Example

name = "Mohit"
Name = "Kumar"

print(name)
print(Name)
    

Multiple Statements

print("Hello")
print("Welcome to Python")
print("Learning Syntax")
    

Comments in Python

Comments are used to explain code and are ignored during execution.

# This is a single-line comment

print("Hello")  # This is an inline comment
    

When to Follow Syntax Rules

• Writing any Python program
• Using conditions and loops
• Defining functions
• Working with classes

Important Concepts

• Indentation replaces curly braces { }
• Each block must have same indentation
• Python code is easy to read due to clean syntax

Tips

• Use 4 spaces for indentation
• Keep code clean and readable
• Use comments to explain logic

Common Mistakes

• Wrong indentation ❌
• Mixing tabs and spaces ❌
• Using wrong case in variables ❌

Variables in Python

A variable is used to store data in a program. It acts like a container that holds values such as numbers, text, or other data.

In Python, you do not need to declare the type of a variable. It is automatically assigned.

Creating Variables

Rules for Naming Variables

Example

                name = "Mohit"
                age = 20
                marks = 85.5
                
                print(name)
                print(age)
                print(marks)
                    

Multiple Assignment

                x, y, z = 10, 20, 30
                print(x, y, z)
                    

Changing Variable Value

                x = 5
                x = 10   # value changed
                print(x)
                    

When to Use Variables

• Storing user input
• Performing calculations
• Saving data for reuse
• Building programs and applications

Important Concepts

• Variables do not need type declaration
• Value can be changed anytime
• Variable names should be meaningful

Tips

• Use clear names like student_name
• Follow lowercase naming style
• Avoid using reserved keywords

Common Mistakes

• Using numbers at start ❌
• Using spaces in names ❌
• Confusing uppercase/lowercase ❌

Data Types in Python

Data Types define the type of value a variable can hold. Python automatically detects the data type based on the value assigned.

Understanding data types is important for performing operations correctly in programs.

Common Data Types

Example

                x = 10          # int
                y = 5.5         # float
                name = "Mohit"  # string
                is_active = True  # boolean
                
                print(x)
                print(y)
                print(name)
                print(is_active)
                    

Checking Data Type

You can check the type of a variable using type() function.

                x = 10
                print(type(x))
                    

Type Conversion

Convert one data type into another using built-in functions.

                x = 10
                y = float(x)   # convert int to float
                
                print(y)
                    

When to Use Data Types

• Performing calculations (int, float)
• Working with text (string)
• Making decisions (boolean)
• Storing structured data

Important Concepts

• Python is dynamically typed
• Same variable can store different data types
• Operations depend on data type

Tips

• Use correct data type for correct operation
• Use type() to debug issues
• Convert types carefully

Common Mistakes

• Mixing string and number ❌
• Wrong type conversion ❌
• Assuming type without checking ❌

Input & Output in Python

Input allows users to enter data into a program, while Output displays the result on the screen.

Python provides simple functions like input() and print() to handle user interaction.

Output using print()

Input using input()

The input() function takes user input as a string.

                name = input("Enter your name: ")
                print("Hello", name)
                    

Example Program

                name = input("Enter your name: ")
                age = input("Enter your age: ")
                
                print("Name:", name)
                print("Age:", age)
                    

Type Conversion with Input

Since input() returns a string, you need to convert it for calculations.

                num1 = int(input("Enter first number: "))
                num2 = int(input("Enter second number: "))
                
                sum = num1 + num2
                print("Sum is:", sum)
                    

Formatted Output

                name = "Mohit"
                age = 20
                
                print(f"My name is {name} and I am {age} years old")
                    

When to Use Input & Output

• Taking user details
• Performing calculations
• Building interactive programs
• Displaying results clearly

Important Concepts

• input() always returns string
• Use int() or float() for numbers
• print() displays output instantly

Tips

• Use clear prompts in input()
• Always convert input when needed
• Use f-strings for clean output

Common Mistakes

• Not converting input to number ❌
• Forgetting quotes in print ❌
• Confusing string with number ❌

Operators in Python

Operators are symbols used to perform operations on variables and values. They are used for calculations, comparisons, and logical decisions.

Python provides different types of operators for different purposes.

Types of Operators

Arithmetic Operators

                x = 10
                y = 5
                
                print(x + y)   # Addition
                print(x - y)   # Subtraction
                print(x * y)   # Multiplication
                print(x / y)   # Division
                print(x % y)   # Modulus
                    

Comparison Operators

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

Logical Operators

                x = 10
                
                print(x > 5 and x < 20)
                print(x > 5 or x > 20)
                print(not(x > 5))
                    

Assignment Operators

                x = 10
                x += 5   # x = x + 5
                x -= 3   # x = x - 3
                
                print(x)
                    

Example Program

                num1 = 20
                num2 = 10
                
                print("Addition:", num1 + num2)
                print("Is num1 greater?", num1 > num2)
                    

When to Use Operators

• Performing calculations
• Making decisions
• Updating variable values
• Combining conditions

Important Concepts

• Operators follow precedence rules
• Comparison operators return True or False
• Logical operators combine conditions

Tips

• Use parentheses for clarity
• Understand operator precedence
• Use logical operators carefully

Common Mistakes

• Using = instead of == ❌
• Wrong operator precedence ❌
• Confusing logical conditions ❌

If Else Conditions in Python

If Else statements are used to make decisions in a program. They allow your code to execute different blocks based on conditions.

Conditions return either True or False, and based on that, Python decides which block of code to run.

Basic If Statement

                age = 18
                
                if age >= 18:
                    print("You are eligible to vote")
                    

If Else Statement

                age = 16
                
                if age >= 18:
                    print("Eligible")
                else:
                    print("Not Eligible")
                    

If Elif Else Statement

                marks = 75
                
                if marks >= 90:
                    print("Grade A")
                elif marks >= 60:
                    print("Grade B")
                else:
                    print("Grade C")
                    

Nested If Statement

                age = 20
                citizen = True
                
                if age >= 18:
                    if citizen:
                        print("Eligible to vote")
                    

Comparison Operators Used

Example Program

                num = int(input("Enter a number: "))
                
                if num % 2 == 0:
                    print("Even Number")
                else:
                    print("Odd Number")
                    

When to Use If Else

• Making decisions in programs
• Validating user input
• Creating conditions in games
• Controlling program flow

Important Concepts

• Indentation is required
• Condition must return True or False
• elif is used for multiple conditions

Tips

• Keep conditions simple and clear
• Use logical operators for complex conditions
• Test all possible cases

Common Mistakes

• Missing indentation ❌
• Using = instead of == ❌
• Wrong condition logic ❌

Loops in Python (for, while)

Loops are used to repeat a block of code multiple times. They help reduce repetition and make programs efficient.

Python mainly provides two types of loops: for loop and while loop.

Types of Loops

For Loop Example

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

This loop prints numbers from 1 to 5.

While Loop Example

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

This loop runs until the condition becomes false.

Break Statement

Used to stop the loop immediately.

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

Continue Statement

Skips current iteration and continues with next.

                for i in range(1, 6):
                    if i == 3:
                        continue
                    print(i)
                    

Nested Loops

                for i in range(1, 4):
                    for j in range(1, 4):
                        print(i, j)
                    

Example Program

                # Print multiplication table of 5
                for i in range(1, 11):
                    print("5 x", i, "=", 5 * i)
                    

When to Use Loops

• Repeating tasks
• Iterating over data
• Generating patterns
• Processing lists and collections

Important Concepts

• Infinite loop occurs if condition never becomes false
• range() is commonly used with for loop
• Loops can be nested

Tips

• Use for loop when iterations are fixed
• Use while loop for conditions
• Be careful with infinite loops

Common Mistakes

• Forgetting to update variable in while loop ❌
• Wrong range values ❌
• Creating infinite loops ❌

Lists in Python

A list is a collection of items stored in a single variable. It is one of the most commonly used data structures in Python.

Lists can store multiple values of different data types and are ordered and changeable.

Creating a List

Accessing List Elements

                students = ["Ram", "Shyam", "Aman"]
                
                print(students[0])   # First element
                print(students[1])   # Second element
                    

Negative Indexing

                print(students[-1])  # Last element
                    

List Operations

Example Program

                fruits = ["Apple", "Banana", "Mango"]
                
                fruits.append("Orange")
                fruits.remove("Banana")
                
                print(fruits)
                    

Looping Through List

                for item in fruits:
                    print(item)
                    

When to Use Lists

• Storing multiple values
• Managing collections of data
• Working with user input lists
• Building applications

Important Concepts

• Lists are ordered and indexed
• Lists are mutable (can be changed)
• Allow duplicate values

Tips

• Use meaningful list names
• Use loops to process lists
• Keep lists organized

Common Mistakes

• Index out of range ❌
• Removing non-existing item ❌
• Confusing list with string ❌

Tuples & Sets in Python

Tuples and Sets are important data structures in Python used to store collections of data.

While both store multiple values, they have different properties and use cases.

Tuple (Immutable Collection)

A tuple is an ordered collection of items that cannot be changed after creation.

Tuple Example

                colors = ("Red", "Green", "Blue")
                
                print(colors[0])
                    

Set (Unordered Collection)

A set is an unordered collection of unique items. It does not allow duplicate values.

Set Example

                numbers = {1, 2, 3, 3, 4}
                
                print(numbers)  # Duplicate removed
                    

Set Operations

Example Program

                set1 = {1, 2, 3}
                set2 = {3, 4, 5}
                
                print("Union:", set1 | set2)
                print("Intersection:", set1 & set2)
                    

When to Use Tuples & Sets

• Tuple → When data should not change
• Set → When you need unique values
• Set → Removing duplicates from list
• Tuple → Fixed data like coordinates

Important Concepts

• Tuple uses ( ) and Set uses { }
• Set does not maintain order
• Tuple is faster than list

Tips

• Use tuple for fixed data
• Use set for unique elements
• Convert list to set to remove duplicates

Common Mistakes

• Trying to change tuple ❌
• Expecting ordered data in set ❌
• Confusing {} with dictionary ❌

Dictionaries in Python

A dictionary is a collection of data stored in key-value pairs. It is used to store related information in a structured way.

Dictionaries are unordered, changeable, and do not allow duplicate keys.

Creating a Dictionary

Accessing Values

                                student = {"name": "Raman", "age": 20}
                                
                                print(student["name"])
                                print(student.get("age"))
                                    

Adding & Updating Items

                                student["marks"] = 90   # Add new key
                                student["age"] = 21     # Update value
                                    

Removing Items

                                student.pop("age")
                                del student["name"]
                                    

Dictionary Methods

Looping Through Dictionary

                                for key, value in student.items():
                                    print(key, ":", value)
                                    

Example Program

                                student = {
                                    "name": "Raman",
                                    "age": 20,
                                    "marks": 85
                                }
                                
                                print("Name:", student["name"])
                                print("Marks:", student["marks"])
                                    

When to Use Dictionaries

• Storing structured data
• Managing user details
• Working with APIs and JSON data
• Building real-world applications

Important Concepts

• Keys must be unique
• Values can be any data type
• Access using key, not index

Tips

• Use meaningful keys
• Use get() to avoid errors
• Keep data structured

Common Mistakes

• Using duplicate keys ❌
• Accessing non-existing key ❌
• Confusing dictionary with list ❌

Functions in Python

A function is a block of code that performs a specific task. It helps in reusing code and makes programs more organized.

Instead of writing the same code again and again, you can define a function and call it whenever needed.

Creating a Function

Basic Function Example

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

Function with Parameters

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

Function with Return Value

                def add(a, b):
                    return a + b
                
                result = add(10, 5)
                print(result)
                    

Default Parameters

                def greet(name="User"):
                    print("Hello", name)
                
                greet()
                greet("Raman")
                    

Lambda Function

                add = lambda a, b: a + b
                print(add(3, 4))
                    

Example Program

                def square(num):
                    return num * num
                
                print(square(5))
                    

When to Use Functions

• Reusing code
• Organizing large programs
• Improving readability
• Breaking complex problems into smaller parts

Important Concepts

• Function must be defined before calling
• Parameters receive input values
• Return sends output back

Tips

• Use meaningful function names
• Keep functions small and simple
• Avoid repeating code

Common Mistakes

• Forgetting to call function ❌
• Missing return statement ❌
• Wrong number of arguments ❌

Modules & Packages in Python

Modules and Packages help organize Python code into reusable files and folders. They make programs more structured and easier to manage.

Instead of writing all code in one file, you can split it into multiple modules.

What is a Module?

A module is a file that contains Python code (functions, variables, classes). It has a .py extension.

Using Built-in Modules

                import math
                
                print(math.sqrt(16))
                print(math.pi)
                    

Import Specific Functions

                from math import sqrt
                
                print(sqrt(25))
                    

Create Your Own Module

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

                # main file
                import mymodule
                
                mymodule.greet("Raman")
                    

What is a Package?

A package is a folder that contains multiple modules. It helps organize large projects.

Package Structure Example

                myproject/
                │
                ├── main.py
                ├── utils/
                │   ├── __init__.py
                │   ├── math_utils.py
                │   └── string_utils.py
                    

Import from Package

                from utils.math_utils import add
                
                print(add(5, 3))
                    

When to Use Modules & Packages

• Organizing large projects
• Reusing code
• Separating logic into files
• Building scalable applications

Important Concepts

• Module = Single file
• Package = Folder of modules
• Use import to access modules

Tips

• Keep modules small and focused
• Use meaningful names
• Organize code logically

Common Mistakes

• Wrong import path ❌
• Missing __init__.py in package ❌
• Naming conflict with built-in modules ❌

File Handling in Python

File Handling allows you to create, read, write, and manage files. It is useful for storing data permanently instead of losing it after program execution.

Python provides built-in functions to work with files easily.

Opening a File

Use the open() function to open a file.

                file = open("data.txt", "r")
                    

Reading a File

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

Writing to a File

                file = open("data.txt", "w")
                file.write("Hello Python")
                file.close()
                    

Appending to a File

                file = open("data.txt", "a")
                file.write("\nNew Line Added")
                file.close()
                    

Using with Statement (Best Practice)

                with open("data.txt", "r") as file:
                    print(file.read())
                    

The with statement automatically closes the file.

Example Program

                with open("student.txt", "w") as file:
                    file.write("Name: Raman\nMarks: 90")
                
                with open("student.txt", "r") as file:
                    print(file.read())
                    

When to Use File Handling

• Saving user data
• Storing logs
• Reading configuration files
• Working with large datasets

Important Concepts

• Always close files after use
• Use correct mode (r, w, a)
• File path must be correct

Tips

• Use with for safe file handling
• Check file existence before reading
• Use newline (\n) for formatting

Common Mistakes

• Forgetting to close file ❌
• Wrong file mode ❌
• File not found error ❌

Exception Handling in Python

Exception Handling is used to handle errors in a program. It prevents the program from crashing and allows smooth execution.

Errors that occur during program execution are called exceptions.

Common Errors

Basic Try-Except

                try:
                    x = int(input("Enter number: "))
                    print(10 / x)
                except:
                    print("Error occurred")
                    

Handling Specific Exceptions

                try:
                    x = int(input("Enter number: "))
                    print(10 / x)
                
                except ZeroDivisionError:
                    print("Cannot divide by zero")
                
                except ValueError:
                    print("Invalid input")
                    

Using Else Block

                try:
                    x = 5
                    print(x)
                
                except:
                    print("Error")
                
                else:
                    print("No error occurred")
                    

Using Finally Block

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

Raising Exceptions

                age = -5
                
                if age < 0:
                    raise ValueError("Age cannot be negative")
                    

Example Program

                try:
                    num1 = int(input("Enter number: "))
                    num2 = int(input("Enter number: "))
                    print(num1 / num2)
                
                except Exception as e:
                    print("Error:", e)
                    

When to Use Exception Handling

• Handling user input errors
• Working with files
• Preventing program crashes
• Building robust applications

Important Concepts

• try → risky code
• except → handle error
• else → runs if no error
• finally → always runs

Tips

• Handle specific exceptions
• Avoid using bare except
• Use finally for cleanup tasks

Common Mistakes

• Using only except without type ❌
• Ignoring errors silently ❌
• Wrong indentation ❌