While Loop.

Sixth class. for is convenient when you know the collection. while repeats as long as the condition is true.

The pattern is: prepare a counter, while condition:, body, update the counter. If you forget the update, the loop may never stop.

Mini example:

n = 1
while n <= 3:
    print(n)
    n = n + 1
print("done")

The condition is checked before each iteration. When it becomes False, while ends and the program continues after the block.

Common mistake: putting n = n + 1 outside the body (or omitting it); or writing while n < 3 when you meant to include 3.