Section Overview

This section introduces loops in Python. Loops let your program repeat actions automatically. You'll learn how to use for and while loops to iterate through data or repeat a block of code until a condition is met.

By the end of this section, you should be able to:

• Use a for loop to repeat an action a fixed number of times
• Use a while loop to repeat based on a condition
• Understand the role of break and continue
• Work with ranges and basic loop patterns

Lesson 1: for Loops and the range() Function

A for loop is used when you want to run something a certain number of times.

for i in range(5):
    print("Hello")

This prints "Hello" five times. The loop variable i goes from 0 to 4.

You can use range(start, stop) to control where the loop begins and ends:

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

This prints numbers 1 to 5.

Lesson 2: Looping Through Strings and Lists

You can use for loops to go through each item in a string or a list:

for letter in "Python":
    print(letter)

colors = ["red", "green", "blue"]
for color in colors:
    print(color)

This pattern is helpful when processing items one at a time.

Lesson 3: while Loops

A while loop keeps running as long as its condition is true.

Example:

count = 0

while count < 3:
    print("Counting:", count)
    count += 1 

Use while when you don’t know in advance how many times you’ll need to loop—like when waiting for user input or checking for a condition.

Lesson 4: break and continue

• break stops the loop early.
• continue skips to the next iteration.

Example:

while True:
    user_input = input("Type 'exit' to quit: ")
    if user_input == "exit":
        break
    print("You typed:", user_input)

This keeps asking for input until the user types "exit".

Another example using continue:

for i in range(5):
    if i == 2:
        continue
    print(i)

This prints 0, 1, 3, 4 — it skips 2.

Quiz: Check Your Understanding

1. What does this print?

for i in range(3):
    print(i)

Answer:
0
1
2

2. What is the main difference between for and while loops?
a) for is faster
b) while is used for strings only
c) for loops a known number of times; while loops as long as a condition is true
Answer: c)

3. What keyword do you use to skip the rest of a loop iteration?
Answer: continue

4. What happens if the condition in a while loop never becomes false?
Answer: The loop runs forever (infinite loop)

Practice Exercise: Countdown Timer

Write a program that:

1. Asks the user to enter a number
2. Counts down to 0, printing each number

Example:

Enter a number: 5 5 4 3 2 1 0
Blast off!

Starter code:

number = int(input("Enter a number: "))

while number >= 0:
    print(number)
    number -= 1

print("Blast off!")

Challenge: Add a short delay between each number using import time and time.sleep(1).