Lists & loops · step 14 of 22

While loops & loop control

10 minRepeat until something changes, and know how to break out.

While something stays true

A while loop repeats for as long as its condition is true. You are responsible for changing something inside, or it never ends.

count = 1
while count <= 3:
    print(count)
    count = count + 1     # or count += 1
print("Done")

for or while?

Use for when you know the items or how many times. Use while when you are waiting for a condition — until a total passes a limit, until the value reaches zero.

break and continue

break leaves the loop immediately; continue skips the rest of this round and starts the next.

number = 0
while True:
    number += 1
    if number == 4:
        break
print(number)     # 4

If a loop never ends, the tab freezes — always check that the value your condition tests actually changes. The code practice here runs in a sandbox with a time limit for exactly that reason.

Remember this

while repeats until its condition is false
Change the tested value inside the loop or it never ends
break exits the loop, continue skips to the next round

Quick quiz

Three questions. 3 correct answers and you have the idea — you can retry as often as you like.

1. What must happen inside a while loop?
2. What does break do?
3. count = 1 with `while count <= 3` — how many times does the block run?

Answer all three to check them.

Now write it yourself

0/2 passed

Practice 1

Print the numbers 1 to 5 with a while loop, one per line.

practice_1.py

Practice 2

Start at 10 and count down by 3 while the value stays above 0, printing each value.

practice_2.py

Finish with two of three quiz answers correct and every exercise passing, and this lesson is marked complete.