Python For Loops: Making Repetition Easy - From Daily Routines to Code

Repetition is Everywhere in Real Life

Think about your daily routine:

• Playing music: Your playlist plays songs one after another, automatically moving to the next song
• Counting money: You go through each note/coin and add to the total

"Life is full of repetitive patterns - we naturally repeat actions until a task is complete!"

Programming has the same need for repetition, and loops are the solution!

Why Are Loops So Important?

Real-World Applications of Loops:

• ATM machines: Process each transaction in your account history
• Social media feeds: Display posts one by one as you scroll

Loops enable automation! They let computers perform repetitive tasks efficiently without human intervention.

😱 The Nightmare Without Loops

Imagine if loops didn't exist in programming...

Problem: Print numbers 1 to 10

Without loops, you'd need 10 print statements:

# The horror of repetitive code!
print(1)
print(2)
print(3)
print(4)
print(5)
print(6)
print(7)
print(8)
print(9)
print(10)

What if you wanted numbers 1 to 100? 1000? 10,000? It would be impractical to write and manage thousands of repetitive lines for such straightforward tasks and it is a worst nightmare when format changes require editing every individual line manually

Without loops, programming would be impractical for real-world applications!

🧠 Natural Intuition for Iteration

You already understand iteration naturally:

Counting Money Example:

Your mental process:
1. Start with total = 0
2. Pick up first note/coin
3. Add its value to total
4. Pick up next note/coin
5. Add its value to total
6. Repeat until no money left
7. Announce final total

This is exactly how programming loops work! You:

• Initialize: Set starting conditions ==> total_value = 0
• Repeat: Perform the same action ==> add the amount to the total_value
• Update: Move to next item ==> pick up the next note/coin
• Stop: When all items processed ==> Do the process still no notes left

Python For Loop Implementation

Basic Syntax:

for variable in sequence:
    # Code to execute repeatedly
    # This block will run once for each item in sequence

Breaking Down the Syntax:

• for: Python keyword that starts the loop
• variable: Name you choose to represent each item (like i, number, item)
• in: Python keyword that connects variable to sequence
• sequence: Collection of items to loop through (list, range, string, etc.)
• :: Colon indicates start of loop body
• Indentation: All code inside loop must be indented (4 spaces recommended)

A sequence is an ordered collection of items where each item has a specific position (index) that you can access using numbers, we have already worked with few sequences, lets have a recap on them

• Strings : 'Vanakkam'   ==> its sequence of individual characters ( 'V','a','n','a','k','k','a','m')
• Lists : [ 1, 2 , 3, 4] ==> its sequence of the items 

as sequence contains multiple items , its best suitable to work with loops to perform operations.

The range() Function - Your Counting Tool

The range() function generates sequences of numbers as List - perfect for counting!

Three Ways to Use range():

By default , Range() generates numbers from 0

Practical Examples:

# Example 1: Count 0 to 4
# range(stop)
print("Counting 0 to 4:")
for i in range(5):
    print(i)

# Output: 0, 1, 2, 3, 4

# Example 2: Count 6 to 10 (natural numbers)
print("First numbers from 6 to 10:")
# range(start, stop)
for number in range(6, 11):
    print(number)

# Output:6, 7, 8, 9, 10

# Example 3: Count by 2s (even numbers)
print("Even numbers from 0 to 10:")
for even in range(0, 11, 2):
    print(even)

# Output: 0, 2, 4, 6, 8, 10

Interactive Examples

Counting Money from Bank

# Build a string by accumulating characters
today_cash_deposits = [ 10 , 4, 6, 8 , 1 , 100, 3, 1000]

print("Started Counting the Money:")
total_deposits_for_the_day = 0 
for cash in today_cash_deposits :                             # Notice that this is not a Range() but a sequece with list data-type
    print(f'Adding {cash} rupees to the Total deposits')
    total_deposits_for_the_day += cash 

print(f"Total deposits for the day: '{total_deposits_for_the_day }'")

Multiplication Table Generator:

# Generate multiplication table for any number
number = int(input("Enter number for multiplication table: "))     # Taking input and converting the data type to Integer

print(f"\nMultiplication table for {number}:")                     # Printing on console
print("=" * 30)                                                    # string multiple operation

for i in range(1, 11):                                             # For loop that iterates from 1 to 10(11-1)
    result = number * i                                            # multiply operation    
    print(f"{number} × {i} = {result}")                            # Print statement with F-strings

Key Takeaways

• Loops solve repetition: They eliminate the need to write the same code multiple times
• For loops iterate over sequences: They process each item in a collection
• range() generates number sequences: Perfect for counting and mathematical operations
• Indentation matters: All code inside the loop must be properly indented

Practice Challenges

Challenge 1: Sum of Even Numbers

# Calculate sum of even numbers from 2 to 20
# Your code here...
# Expected output: 2+4+6+8+10+12+14+16+18+20 = 110

Challenge 2: Factorial Calculator

# Calculate factorial of a number (n!)
# For example: 5! = 5 × 4 × 3 × 2 × 1 = 120
# Your code here...

Challenge 3: Pattern Printer

# Print this pattern:
# *
# **
# ***
# ****
# *****
# Your code here...

Coming Up Next

Excellent! You now understand how to make Python repeat tasks efficiently using for loops. You've learned about:

• Why repetition is important in programming
• How for loops save you from writing repetitive code
• Using range() for counting and number sequences
• Accumulation patterns for building results

In our next lesson, we'll explore While Loops and Advanced Loop Techniques - learning how to create loops that run until specific conditions are met, just like how you might keep trying something until you succeed!

You're mastering the art of automation!