leedcode 合并两个有序链表

class Solution(object):
    def mergeTwoLists(self, list1, list2):
        if not list1:
            return list2
        if not list2:
            return list1
        result = None
        while list1 or list2:
            if not (list1 and list2):
                while list1:
                    result = ListNode(list1.val,result)
                    list1 = list1.next
                while list2:
                    result = ListNode(list2.val,result)
                    list2 = list2.next
            else:
                if list1.val < list2.val:
                    result = ListNode(list1.val,result)
                    list1 = list1.next
                else:
                    result = ListNode(list2.val, result)
                    list2 = list2.next
        result2 = None
        while result:
            result2 = ListNode(result.val,result2)
            result = result.next
        return result2