code: 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
docs: Returns True if number is valid according to mod10.