code: def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
      carry = 0
  
      z = None
      x = l1
      y = l2
  
      while x or y:
          if x and y:
              sumxy = x.val + y.val + carry
          if x is None:
              sumxy = y.val + carry
          if y is None:
              sumxy = x.val + carry
  
          zval = sumxy % 10
          carry = int(sumxy / 10)
  
          tnode = ListNode(zval)
          if z is None:
              z = tnode
              nextnode = z
          else:
              nextnode.next = tnode
              nextnode = nextnode.next
          if x:
              x = x.next
          if y:
              y = y.next
      if carry > 0:
          tnode = ListNode(carry)
          nextnode.next = tnode
      return z
  
label_desc: Use image node_id 1 for calling the Solution obj's underlying member method code with example usage: obj.addTwoNumbers(l1, l2) and returns: z