A while loop repeats a block of code for as long as its condition is True. It checks the condition, runs the body, then checks again — over and over.

count = 1

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

print("Done!")

Read it as: "while count is less than or equal to 5, print it and add one."

Like if, a while needs a colon and an indented body.

The three parts of every loop

Nearly every while loop has these, and forgetting any one causes a bug:

1. Setup — a variable exists before the loop (count = 1).
2. Condition — something that will eventually become False (count <= 5).
3. Update — the body changes the variable (count = count + 1).

Infinite loops

If the condition never becomes False, the loop never stops:

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

That prints 1 forever, because nothing ever changes count. If you run something like this in the editor below and it hangs, click Reset. The fix is almost always a missing update step.

Shorthand: +=

count = count + 1 is so common that Python has a shortcut:

count = 0
count += 1
count += 5
print(count)

-=, *=, and /= work the same way.

Counting down

Loops can go in any direction — just adjust the condition and the update.

countdown = 3

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

print("Liftoff!")

Try it yourself

Print the numbers 1 through 5, one per line, using a while loop.

Checkpoint

• while repeats as long as its condition stays True.
• Every loop needs setup, a condition that can end, and an update.
• Forgetting the update creates an infinite loop.
• += is shorthand for "add to this variable."