While Loops

The Magic Merry-Go-Round: Python While Loops

Imagine a merry-go-round that keeps spinning until someone says “STOP!” That’s exactly how while loops work in Python!

What is a While Loop?

Think of a while loop like this:

“Keep doing this thing… while this is true.”

It’s like telling your little robot friend:

• “Keep eating cookies while you’re still hungry”
• “Keep running while the music plays”
• “Keep counting while we haven’t reached 10”

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

What happens?

1
2
3
4
5

The loop checks: “Is count still 5 or less?” If yes, keep going! Once count becomes 6, the ride stops.

While Loop Basics

The Recipe

Every while loop has three simple parts:

graph TD
    A["Start with something"] --> B{Check condition}
    B -->|True| C["Do something"]
    C --> D["Change something"]
    D --> B
    B -->|False| E["Exit loop"]

A Simple Example

Let’s make a countdown like a rocket launch:

countdown = 5
while countdown > 0:
    print(countdown)
    countdown = countdown - 1
print("BLAST OFF!")

Output:

5
4
3
2
1
BLAST OFF!

The Golden Rule

Always change something inside your loop!

If you forget, your merry-go-round will spin forever!

# BAD - Never ends!
x = 1
while x < 5:
    print(x)
    # Oops! We forgot: x = x + 1

Break Statement: The Emergency Exit

What is Break?

Imagine you’re on that merry-go-round, and suddenly you see an ice cream truck. You want to jump off immediately!

That’s what break does. It says: “STOP right now! I’m getting off!”

number = 1
while number <= 10:
    if number == 5:
        print("Found 5! Jumping off!")
        break
    print(number)
    number = number + 1

Output:

1
2
3
4
Found 5! Jumping off!

See? We never reached 10. Once we found 5, we broke out!

Real-Life Example: Finding a Toy

toys = ["car", "ball", "teddy", "robot"]
index = 0

while index < len(toys):
    if toys[index] == "teddy":
        print("Found my teddy!")
        break
    print(f"Checking {toys[index]}...")
    index = index + 1

Output:

Checking car...
Checking ball...
Found my teddy!

Continue Statement: Skip and Keep Going

What is Continue?

Imagine you’re picking apples. You see a rotten one. Do you stop picking? No! You just skip that apple and keep going.

continue says: “Skip this round, but keep the loop running!”

number = 0
while number < 5:
    number = number + 1
    if number == 3:
        print("Skipping 3!")
        continue
    print(number)

Output:

1
2
Skipping 3!
4
5

Notice how 3 was skipped, but we kept going to 4 and 5!

The Difference

graph TD
    A["break"] --> B["Stops entire loop"]
    C["continue"] --> D["Skips current round only"]

Pass Statement: The “Do Nothing” Placeholder

What is Pass?

Sometimes you need to write a loop but haven’t decided what goes inside yet. It’s like saving a seat for a friend who isn’t here yet.

pass says: “I’m here, but I’ll do nothing for now.”

count = 0
while count < 3:
    count = count + 1
    pass  # TODO: Add code later

This runs without errors, even though we’re not doing anything useful yet!

When to Use Pass

• Planning your code structure
• Creating placeholder loops
• When syntax requires something but you’re not ready

# Placeholder for future logic
while True:
    pass  # Will add game logic later

Note: Using pass in a while True loop creates an infinite loop that does nothing. Only use this as a temporary placeholder!

Assignment Expressions: The Walrus Operator

What is It?

Python 3.8 introduced a cool trick called the walrus operator :=

It looks like a walrus! → := (two eyes and tusks!)

It lets you assign and check at the same time.

Before (The Old Way)

line = input("Type something: ")
while line != "quit":
    print(f"You said: {line}")
    line = input("Type something: ")

We had to write input() twice!

After (The Walrus Way)

while (line := input("Type: ")) != "quit":
    print(f"You said: {line}")

One line does two jobs:

1. Gets input and stores it in line
2. Checks if it equals “quit”

Another Example

Reading numbers until we get 0:

while (num := int(input("Number: "))) != 0:
    print(f"Square is {num * num}")
print("Done!")

The := assigns and returns the value at the same time. Magic!

Loop Else Clause: The “Finish Line” Prize

What is Loop Else?

This is Python’s special superpower! A while loop can have an else block.

The else runs only if the loop finished normally (without a break).

Think of it like a marathon:

• If you finish the race → You get a medal (else runs)
• If you quit early → No medal (else skips)

Example: Searching for a Number

target = 7
current = 1

while current <= 5:
    if current == target:
        print("Found it!")
        break
    current = current + 1
else:
    print("Not found in range")

Output:

Not found in range

Since we never found 7, we finished normally, so else ran!

When Break Is Used

target = 3
current = 1

while current <= 5:
    if current == target:
        print("Found it!")
        break
    current = current + 1
else:
    print("Not found")

Output:

Found it!

The else didn’t run because we used break!

Summary Table

Putting It All Together

Let’s build a simple guessing game using everything we learned:

secret = 7
guess = 0

while (guess := int(input("Guess: "))) != secret:
    if guess == 0:
        print("Giving up!")
        break
    elif guess < secret:
        print("Too low!")
        continue
    else:
        print("Too high!")
else:
    print("You got it!")

What’s happening:

• := assigns and checks the guess
• break exits if player gives up
• continue skips to next guess
• else celebrates when found!

Quick Reference

graph TD
    A["while condition:"] --> B{Is condition true?}
    B -->|Yes| C["Run loop body"]
    C --> D{Hit break?}
    D -->|Yes| E["Exit - NO else"]
    D -->|No| F{Hit continue?}
    F -->|Yes| B
    F -->|No| G["Finish body"]
    G --> B
    B -->|No| H["Run else if exists"]
    H --> I["Exit loop"]

You Did It!

You now understand the complete magic of Python while loops! You know:

• How while loops repeat code
• How to escape with break
• How to skip with continue
• How to hold space with pass
• How to be clever with :=
• How to reward completion with else

The merry-go-round of learning never stops, but now you control it!