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For Loop in Python

  • This lesson explains how to use the for loop in Python to iterate over lists, strings, and ranges with practical examples.

  • What is a Loop?

    A loop in Python is a programming structure used to repeat a block of code multiple times until a specific condition is met.

    👉 Instead of writing the same code again and again, loops automate repetition.

    Why Do We Use Loops?

    We use loops to:

    • Avoid writing repeated code

    • Save time and reduce code length

    • Perform repetitive tasks efficiently

    • Work with collections (lists, strings, numbers)

    • Automate processes

Problem Without Loop

If you want to print numbers from 1 to 5 without a loop, you must write: 

print(1)
print(2)
print(3)
print(4)
print(5)

  • This is time-consuming and not practical.

Solution Using Loop 

for i in range(1, 6):
    print(i)
    • Short
    • Clean
    • Efficient

  • Real-Life Examples of Loops

    Real Life

    Loop Concept

    Washing clothes

    Repeat wash until clean

    Attendance

    Mark each student one by one

    ATM PIN tries

    Repeat until correct

    Traffic signals

    Repeat cycle continuously

    Where Are Loops Used?

    Loops are commonly used in:

    • Printing patterns

    • Processing lists and strings

    • Calculations (sum, average)

    • Login attempts

    • Games and animations

    • Data processing

    Types of Loops in Python

    Python supports three main looping statements:

    1. for loop

    2. while loop

    3. nested loops

    Loop Control Statements

    Statement

    Purpose

    break

    Stops the loop

    continue

    Skips current iteration

    pass

    Does nothing (placeholder)



    Flow of Loop Execution

    1. Loop starts

    2. Condition is checked

    3. Code block executes

    4. Update happens

    5. Condition re-checked

    6. Loop ends when condition is False

    Advantages of Loops

    • Reduces code repetition
    • Improves readability
    • Easy to maintain
    • Efficient execution

  • What is a for Loop?

    The for loop in Python is used to repeat a block of code for each item in a sequence such as:

    • range of numbers

    • list

    • string

    • tuple

    • dictionary

    The loop runs once for each value in the sequence.

    Why Use a for Loop?

    We use a for loop when:

    • The number of repetitions is known

    • We want to iterate over data

    • Repetitive tasks must be automated

    • Clean and readable code is required

    Syntax of for Loop

    General Syntax

    for variable in sequence:

        statement(s)

    Syntax Explanation

    Part

    Description

    for

    Loop keyword

    variable

    Stores each value from sequence

    in

    Connects variable with sequence

    sequence

    Collection or range

    :

    Start of loop block

    Indentation

    Defines loop body

    Using range() with for Loop

    range() Function

    range(start, stop, step)

    • start → starting value (default 0)

    • stop → ending value (excluded)

    • step → increment/decrement (default 1)

Printing Numbers Using for Loop

This program prints numbers from 1 to 5 using a for loop. 

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

Repeating Message Using for Loop

This program prints a welcome message 3 times using a for loop. 

for count in range(3):
    print("Welcome to Python")

Displaying List Items Using for Loop

This program prints each element from a list using a for loop. 

fruits = ["Apple", "Banana", "Mango"]

for fruit in fruits:
    print(fruit)

Printing Each Character Using for Loop

This program prints each character of a string one by one. 

name = "Python"

for ch in name:
    print(ch)

Printing Even Numbers Using for Loop

This program prints even numbers between 2 and 10 using a step value. 

for i in range(2, 11, 2):
    print(i)

Nested for Loop Demonstration

This program uses a loop inside another loop to show nested iteration. 

for i in range(1, 4):
    for j in range(1, 3):
        print(i, j)

  • What is else with for Loop?

    In Python, a for loop can have an else block.

    The else block is executed:

    • ✅When the loop completes normally

    • ❌ Not executed if the loop is stopped using break

    👉 This feature is unique to Python and often misunderstood.

    Why Use else with for Loop?

    We use else with a for loop to:

    • Confirm that a loop finished without interruption

    • Handle search operations

    • Avoid using extra flags (True/False)

    • Write clean and logical code

    Basic Syntax of for-else

    for variable in sequence:

        statement(s)

    else:

        statement(s)

Using else with for Loop (No break)

This program demonstrates how the else block executes when the loop finishes normally. 

for i in range(1, 6):
    print(i)
else:
    print("Loop completed successfully")

  • Explanation

    • Loop runs from 1 to 5

    • No break is used

    • else block executes at the end

Using else with for Loop and break

This program shows that the else block does NOT execute when the loop is terminated using break. 

for i in range(1, 6):
    if i == 3:
        break
    print(i)
else:
    print("Loop completed")

  • Explanation

    • Loop stops when i == 3

    • break is executed

    • else block is skipped

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