new_contents: class Solution:
      def addStrings(self, num1, num2):
          """
          :type num1: str
          :type num2: str
          :rtype: str
          """
          ret = []
          l1 = len(num1) - 1
          l2 = len(num2) - 1
          flag = 0
          while l1 >= 0 and l2 >= 0:
              n1 = ord(num1[l1]) - 48
              n2 = ord(num2[l2]) - 48
              if n1 + n2 + flag > 9:
                  ret.append(n1+n2+flag-10)
                  flag = 1
              else:
                  ret.append(n1+n2+flag)
                  flag = 0
              l1 -= 1
              l2 -= 1
              
          while l1 >= 0:
              n1 = ord(num1[l1]) - 48
              if flag:
                  if n1+flag > 9:
                      ret.append(n1+flag-10)
                      flag = 1
                  else:
                      ret.append(n1+flag)
                      flag = 0
              else:
                  ret.append(n1)
              l1 -= 1
              
          while l2 >= 0:
              n2 = ord(num2[l2]) - 48
              if flag:
                  if n2+flag > 9:
                      ret.append(n2+flag-10)
                      flag = 1
                  else:
                      ret.append(n2+flag)
                      flag = 0
              else:
                  ret.append(n2)
              l2 -= 1   
          if flag:
              ret.append(flag)
  
          if len(ret) == 1:
              return str(ret[0])
          final = 0
          for i in range(len(ret)):
              final += (10 ** i) * ret[i]
          return str(final)
  
subject: Add Strings