LeetCode：Add Two Numbers

The problem is described as following:

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

My solution is as following(in Python ):

# Definition for singly-linked list.# class ListNode:#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution:    # @return a ListNode    def addTwoNumbers(self, l1, l2):        re = ListNode(0)        cur = re        temp = 0        while not (l1 == None  and l2 ==None):            extra = temp            if l1 != None :                extra += l1.val                l1 = l1.next            if l2 != None :                extra += l2.val                l2 = l2.next            temp = extra/10            cur.next = ListNode(extra%10)            cur = cur.next        if temp != 0:            cur.next = ListNode(temp)        return re.next