'Returns True if number is valid according to mod10.'

def is_mod10(self):

    double = 0
    total = 0
    for i in range((len(self.number) - 1), (-1), (-1)):
        for c in str(((double + 1) * int(self.number[i]))):
            total = (total + int(c))
        double = ((double + 1) % 2)
    return ((total % 10) == 0)
