循环列表以删除项目 - 意外行为

Question

未按预期工作的简化方案。我希望有人能指出原因。

nums = [0, 0, 4, 0]
new_list = nums
for i in range(len(nums)):
  if nums[i] !=0:
    break
  del new_list[0]
new_list

我正在尝试删除前面的零。我希望上面的循环删除列表的第一个元素直到它遇到一个非零数字，然后中断。它只是删除第一个零，即使我的 del new_list[0] 语句在循环中。

预期输出：[4, 0] 实际输出：[0, 4, 0]

Answer 1

nums = [0, 0, 4, 0]
new_list = nums # this refer to nums and when you change new_list, nums changes
# do following to make a copy.
new_list = nums[::]
for i in range(len(nums)):
  if nums[i] !=0:
    break
  del new_list[0]
new_list

输出

[4, 0]

Answer 2

python 中的赋值运算符（如 new_list = nums 中所用）不会创建新对象，而只是将另一个名称分配给现有对象。您对 nums 所做的任何更改也会影响 new_list。

要创建新对象，您可以改为制作浅拷贝：

new_list = nums.copy()

Answer 3

在 python 中，赋值运算符不会在您的 casenum 中使您成为对象的新实例。我建议你阅读 python 中的深拷贝和浅拷贝。正如this article所说

In Python, Assignment statements do not copy objects, they create bindings between a target and an object. When we use = operator user thinks that this creates a new object; well, it doesn’t. It only creates a new variable that shares the reference of the original object. Sometimes a user wants to work with mutable objects, in order to do that user looks for a way to create “real copies” or “clones” of these objects. Or, sometimes a user wants copies that user can modify without automatically modifying the original at the same time, in order to do that we create copies of objects.

您可以使用复制模块进行深度复制。

import copy


nums = [0, 0, 4, 0]  
new_list = copy.deepcopy(nums) # using deepcopy for deepcopy

循环列表以删除项目 - 意外行为

Looping over list to delete items - unexpected behavior

python

list

loops

del