python三元if语句没有捕获None

Question

我正在实现从 python 中的两个链表中添加两个数字的算法。 (来自破解编码面试2-5)

例如，

first: 7 -> 1 -> 6      617
second: 5 -> 9 -> 2    +295
                       -----
                        912
output: 2 -> 1 -> 9 ( which indicates 912 )

这是我的代码

class Node:
    def __init__(self, val=None):
        self.data = val
        self.Next = None

class LinkedList:
    def __init__(self):
        self.head = None
        self.size = 0

    def __repr__(self):
        temp = self.head
        alist = []
        while temp:
            alist.append(temp.data)
            temp = temp.Next
        return str(alist)

    def add(self, val):
        cur = self.head
        prev = None
        if cur is None:
            self.head = Node(val)
        else:
            while cur:
                prev = cur
                cur = cur.Next
            prev.Next = Node(val)
        self.size += 1

def adding(p1,p2):
    pointer1 = p1.head
    pointer2 = p2.head
    remainder = 0
    sum_list = LinkedList()

    while pointer1 is not None or pointer2 is not None:
        first = 0 if pointer1.data is None else pointer1.data
        second = 0 if pointer2.data is None else pointer2.data
        sum_ = first + second + remainder

        remainder = 1 if sum_ >= 10 else 0

        sum_ %= 10

        sum_list.add(sum_)

        if pointer1 is not None:
            pointer1 = pointer1.Next
        if pointer2 is not None:
            pointer2 = pointer2.Next
    if remainder > 0:
        sum_list.add(remainder)
    return sum_list

我的问题是 first = 0 if pointer1.data is None else pointer1.data .
当两个链表的大小相同时它起作用，但是，如果一个比另一个短，则较短的变成None .所以我希望我的 if 语句能捕捉到这一点并使变量(首先)为 0 .然而它抛出 AttributeError: NoneType object has no attribute 'data' .

如果我正常写入，它就可以工作，而不是 ternary operator

if pointer1 is None:
    first = 0
else:
    first = pointer1.data
if pointer2 is None:
    second = 0
else:
    second = pointer2.data

我在使用 ternary operator 时是否遗漏了什么？ ?
谢谢!

Answer 1

是的，您实际上并没有执行 if/else 语句对三元运算符所做的操作。

这个:

if pointer1 is None:
    first = 0
else:
    first = pointer1.data
if pointer2 is None:
    second = 0
else:
    second = pointer2.data

将是以下内容:

first = 0 if pointer1 is None else pointer1.data
second = 0 if pointer2 is None else pointer2.data

在您的版本中:

first = 0 if pointer1.data is None else pointer1.data

可能是 pointer1是 None，因此没有 data属性，这就是您收到异常的原因。所以你需要检查pointer1不是 None访问前 data .