Python代码如下：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        head = ListNode(0)
        current = head
        carry = 0
        while(l1 or l2):
            if (l1):
                x = l1.val
            else:
                x = 0
            if (l2):
                y = l2.val
            else:
                y = 0
            sum = carry+x+y
            carry = sum // 10
            current.next = ListNode(sum%10)
            current = current.next
            if(l1!= None): l1 = l1.next
            if(l2!= None): l2 = l2.next
        if (carry>0):
            current.next = ListNode(1)
        return head.next
            

链表的存储，我这里使用了头结点，用于指向链表的第一个元素。