Loops That Repeat: while 🔁

while: keep going until

grog = 5

while grog > 0:
    print(f"{grog} mugs of grog on the wall")
    grog -= 1

print("The bar is dry.")

5 mugs of grog on the wall
4 mugs of grog on the wall
3 mugs of grog on the wall
2 mugs of grog on the wall
1 mugs of grog on the wall
The bar is dry.

The shape is always the same, and it has exactly three moving parts:

1. Set something up before the loop (grog = 5).
2. Ask a question at the top. True means go round again, false means stop.
3. Change something inside the loop so the answer eventually becomes false (grog -= 1).

Miss step three and the loop runs forever. Which is next.

The infinite loop, and the escape hatch

grog = 5

while grog > 0:
    print("still 5 mugs, forever, until the heat death of the universe")
    # grog never changes, so the condition is never false

In this school's playground, the run button gives up after twenty seconds and tells you so, which is friendlier than freezing your browser. On your own machine, Ctrl+C is the answer. Writing an infinite loop is a rite of passage, not a disaster, and everybody has done it.

Waiting for the right answer

answer = ""

while answer != "swordfish":
    answer = input("Password: ")
    if answer != "swordfish":
        print("  That is not the password.")

print("The door swings open.")

Password: grog
  That is not the password.
Password: monkey
  That is not the password.
Password: swordfish
The door swings open.

This is the classic use of while: you do not know in advance how many times it will run. That is the whole difference between while and the for loop in the next lesson. Unknown number of repeats: while. Known collection to walk through: for.

break: leave immediately

while True:
    command = input("> ")
    if command == "quit":
        print("Farewell.")
        break
    print(f"You try to {command}. Nothing happens.")

> look
You try to look. Nothing happens.
> take grog
You try to take grog. Nothing happens.
> quit
Farewell.

while True: with a break inside is a completely respectable pattern, not a cheat. It says "loop until I decide to stop", and it is the standard shape for menus, game loops and command prompts. The important thing is that a break exists somewhere and is reachable.

continue: skip the rest of this round

number = 0

while number < 10:
    number += 1
    if number % 2 == 0:
        continue          # jump straight back to the top
    print(f"{number} is odd")

1 is odd
3 is odd
5 is odd
7 is odd
9 is odd

while / else, a Python curiosity

attempts = 3

while attempts > 0:
    print(f"{attempts} attempts left")
    attempts -= 1
else:
    print("Ran out of attempts, and no break happened.")

3 attempts left
2 attempts left
1 attempts left
Ran out of attempts, and no break happened.

The else on a loop runs only if the loop finished naturally, without a break. It is genuinely useful for searches ("if we got through the whole list without finding it..."), rare in the wild, and confusing enough that many style guides discourage it. Know it exists so it does not startle you in someone else's code.

A real one: the number guessing game

import random

secret = random.randint(1, 100)
guesses = 0

while True:
    guess = int(input("Guess (1-100): "))
    guesses += 1

    if guess < secret:
        print("  Higher.")
    elif guess > secret:
        print("  Lower.")
    else:
        print(f"Got it in {guesses} guesses.")
        break

That is a complete, genuinely fun program in fourteen lines, and it is Project 1 in the workshop, where you build it properly with input validation and a play-again loop.

n = 10

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

print("Liftoff! 🚀")

10
9
8
7
6
5
4
3
2
1
Liftoff! 🚀

total = 0
count = 0

while True:
    number = int(input("Number (0 to finish): "))
    if number == 0:
        break
    total += number
    count += 1

print(f"{count} numbers, total {total}")

Number (0 to finish): 5
Number (0 to finish): 10
Number (0 to finish): 3
Number (0 to finish): 0
3 numbers, total 18

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

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

1
2
3
4