when to stop when number is not a happy number

Question

A happy number is defined by the following process. Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process un

Answer 1

You can detect unhappy numbers with a constant amount of memory. According to Wikipedia, for any positive integer starting point, the sequence will terminate at one, or loop forever at 4, 16, 37, 58, 89, 145, 42, 20, 4. Since no other loops exist, it is easy to test for unhappiness.

def isHappy(x):
    while True:
        if x == 1:
            return True
        if x == 4:
            return False
        x = nextNumberInSequence(x)