Add Two numbers

# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class (object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        result = ListNode(0)
        head = result
        flag = 0
        while l1 != None and l2 != None:
            sum = l1.val + l2.val + flag
            next = ListNode(sum % 10)
            flag = sum / 10
            head.next = next
            head = head.next
            l1 = l1.next
            l2 = l2.next
        l = l1
        if(l1 == None):
            l = l2
        while l != None:
            sum = l.val + flag
            next = ListNode(sum % 10)
            flag = sum / 10
            head.next = next
            head = head.next
            l = l.next
        if(flag != 0):
            next = ListNode(flag)
            head.next = next
        return result.next