Question

代码：

class Stack:
    def __init__(self):
        self.items = []

    def is_empty(self):
        return self.items == []

    def push(self, item):
        self.items.append(item)

    def pop(self):
        return self.items.pop()

def length(stack):
    i = 0
    while not stack.is_empty():
        stack.pop()
        i += 1
    return i

s1 = Stack()
s1.push(3)
s1.push(2)
s1.push(1)
print(length(s1))
s1.pop()

输出：

3
Traceback (most recent call last):
  File "Stack.py", line 26, in <module>
    s1.pop()
  File "Stack.py", line 12, in pop
    return self.items.pop()
IndexError: pop from empty list

我希望函数length()能够修改s1的副本，而不是更改s1。有没有办法在python中做到这一点？

我不允许直接使用s1.items，因此我无法使用s1[:]。我也无法修改课程。

Answer 1

您只需使用copy模块：

import copy

# ... your code ...

print(length(copy.deepcopy(s1)))  # pass a copy to the length function

或者如果你想要它没有额外的模块，如果你可以改变length功能，你可以简单地保留pop ped项目和push它们的长度：< / p>

def length(stack):
    i = 0
    tmp = []
    while not stack.is_empty():
        tmp.append(stack.pop())    # append them to your temporary storage
        i += 1
    for item in tmp:               # take the items saved in the temporary list
        stack.push(item)           # and push them into your stack again
    return i

按值传递对象参数

1 个答案: