python 中的赋值语句在更改函数调用的位置后给出不同的结果

Question

为什么

is_correct =  list(llist) == list(reverse(flipped))

is_correct 输出 False 但

is_correct =  list(reverse(flipped)) == list(llist)

is_correct 输出 True

我正在编写代码来反转链表所以

reverse() 的功能是反转链表
flipped 和 llist 是如下所示的 LinkedList 对象。

完整代码是

class Node:
    def __init__(self, value):
        self.value = value
        self.next = None

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

    def __init__(self):
        self.head = None

    def append(self, value):
        if self.head is None:
            self.head = Node(value)
            return

        node = self.head
        while node.next:
            node = node.next

        node.next = Node(value)

    def __iter__(self):
        node = self.head
        while node:
            yield node.value
            node = node.next

    def __repr__(self):
        return str([v for v in self])

def reverse(linked_list):

    head = linked_list.head
    nh = head.next
    head.next = None
    while nh:
        temp = nh.next
        nh.next = head
        head = nh
        nh = temp
    linked_list.head = head
    return linked_list

llist = LinkedList()
li = [4,2,5,1,-3,0]
for value in li:
    llist.append(value)

flipped = reverse(llist)
is_correct =  list(llist) == list(reverse(flipped))
print("Pass" if is_correct else "Fail")

llist = LinkedList()
li = [4,2,5,1,-3,0]
for value in li:
    llist.append(value)

flipped = reverse(llist)
is_correct =  list(reverse(flipped)) == list(llist) 
print("Pass" if is_correct else "Fail")

提前致谢！！！

Answer 1

鉴于reverse是一个就地操作，你的代码等同于

flipped = reverse(llist)  # two names for the same reversed list
t1 = list(llist)  # a copy of the reversed list
t2 = list(reverse(flipped)) # a copy of the re-reversed list, identical to the original
is_correct = t1 == t2  # False; one is in the original order, the other reverse order

flipped = reverse(llist)  # two names for the same reversed list
t1 = list(reverse(flipped)) # a copy of the re-reversed list
t2 = list(llist) # another copy of the re-reversed list
is_correct = t1 == t2  # True; both lists are in the original non-reversed order

== 的操作数是从左到右求值的，因此 reverse 是第一次调用还是第二次调用会影响创建的 list 个对象。

python 中的赋值语句在更改函数调用的位置后给出不同的结果

Assignment statement in python giving different results after changing the position of function calls

python

variable-assignment