':type num1: str
:type num2: str
:rtype: str'

def addStrings2(self, num1, num2):

    length = max(len(num1), len(num2))
    num1 = num1.zfill(length)[::(-1)]
    num2 = num2.zfill(length)[::(-1)]
    (res, plus) = ('', 0)
    for (index, num) in enumerate(num1):
        tmp = str(((int(num) + int(num2[index])) + plus))
        res += tmp[(-1)]
        if (int(tmp) > 9):
            plus = 1
        else:
            plus = 0
    if plus:
        res += '1'
    return res[::(-1)]
