Happy Number

Write an algorithm to determine if a number is "happy".

A happy number is a number 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 until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Example: 19 is a happy number

1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 02 = 1

class Solution(object):
    def isHappy(self, n):
        """
        :type n: int
        :rtype: bool
        """
        box = set()
        while n != 1:
            n = sum(int(x) ** 2 for x in str(n))
            if n in box:
                return False
            else:
                box.add(n)
        return True