Module 9 of 15 · Step 1 of 12

while Loops

A while loop repeats while a condition is True. Unlike a for loop, it does not automatically move to the next value. You must update something so it can stop.

By the end of this lesson, you can:

Write a stopping condition
Update a loop variable
Count upward and downward
Recognize an infinite loop
Repeat input until a match

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Learn · Repeat while a condition is true

Concept 1 of 5

Repeat while a condition is true

Python checks the condition before every repetition. When it becomes False, the loop ends. The body must be indented and should change a value used by the condition.

Pattern

while condition:
    instruction
    update

Code

count = 1
while count <= 4:
    print(count)
    count += 1

Output

Why it works

count starts at 1.
The condition allows values through 4.
count increases each time; at 5 the loop stops.

Common mistake

Not this

while count <= 4:
    print(count)

Try this

while count <= 4:
    print(count)
    count += 1

Without an update, count never changes and the loop may run forever.