while loops

while condition: keeps running the block as long as the condition is true. Use it when you do not know in advance how many times to loop: keep dividing until the number is gone, keep asking until the answer is right. Something inside the block must change the condition, or the loop never ends (the lesson runner will stop it after a few seconds and tell you).

A common shape is a counter: set it before the loop, test it in the condition, change it in the body. n //= 10 is the shorthand for n = n // 10.

n = 1
steps = 0
while n < 100:
    n *= 2
    steps += 1
print(n, steps)   # 128 7

Your task

Write digits(n) that returns how many digits a non-negative whole number has by repeatedly floor-dividing by 10 (digits(0) is 1), and collatz_steps(n): while n is not 1, replace it with n / 2 when even or 3n + 1 when odd, and return how many steps it took.

def digits(n):
    if n == 0:
        return 1
    count = 0
    while n > 0:
        n //= 10
        count += 1
    return count


def collatz_steps(n):
    steps = 0
    while n != 1:
        if n % 2 == 0:
            n = n // 2
        else:
            n = 3 * n + 1
        steps += 1
    return steps