445 add two numbers ii

def (self, l1, l2):
  def valueofList (ls):
      val = 0
      while ls != None:
          val = val *10+ls.val
          ls = ls.next
      return val
  strsum = str(valueofList(l1)+valueofList(l2))
  root = ListNode(int(strsum[0]))
  p1 = root
  for i in range(1,len(strsum)):
      node = ListNode(strsum[i])
      p1.next = node
      p1 = node
  return root