为什么带有 pop 方法(或 del 语句)的 for 循环不遍历所有列表元素 [英] Why does a for-loop with pop-method (or del statement) not iterate over all list elements

问题描述

我是 Python 新手，正在尝试使用列表我在 linux2 上使用 Python 3.2.3(默认，2012 年 10 月 19 日，20:13:42)，[GCC 4.6.3]

这是我的示例代码

<预><代码>>>>l=[1,2,3,4,5,6]>>>对于我在 l:... l.pop(0)...打印(升)...

我希望得到以下输出

1[2, 3, 4, 5, 6]2[3, 4, 5, 6]3[4, 5, 6]4[5, 6]5[6]6[]

相反，我得到了这个

1[2, 3, 4, 5, 6]2[3, 4, 5, 6]3[4, 5, 6]

for 循环在 3 圈后停止迭代.有人能解释一下原因吗?

解决方案

展开一点(插入符号 (^) 位于循环索引"处):

your_list = [1,2,3,4,5,6]^

弹出第一个项目后:

your_list = [2,3,4,5,6]^

现在继续循环:

your_list = [2,3,4,5,6]^

现在弹出第一项:

your_list = [3,4,5,6]^

现在继续循环:

your_list = [3,4,5,6]^

现在弹出第一项:

your_list = [4,5,6]^

现在继续循环——等等，我们完成了.:-)

<小时><预><代码>>>>l = [1,2,3,4,5,6]>>>对于 x 中的 l:... l.pop(0)...123>>>打印 l[4, 5, 6]

I am new to Python and experimenting with lists I am using Python 3.2.3 (default, Oct 19 2012, 20:13:42), [GCC 4.6.3] on linux2

Here is my samplecode

>>> l=[1,2,3,4,5,6]
>>> for i in l:
...     l.pop(0)
...     print(l)
... 

I would expect the following output

1
[2, 3, 4, 5, 6]
2
[3, 4, 5, 6]
3
[4, 5, 6]
4
[5, 6]
5
[6]
6
[]

Instead I am getting this

1
[2, 3, 4, 5, 6]
2
[3, 4, 5, 6]
3
[4, 5, 6]

The for-loop stops iterating after 3 turns. Can somebody explain why?

解决方案

Unrolling a bit (the caret (^) is at the loop "index"):

your_list = [1,2,3,4,5,6]
             ^

after popping off the first item:

your_list = [2,3,4,5,6]
             ^

now continue the loop:

your_list = [2,3,4,5,6]
               ^

Now pop off the first item:

your_list = [3,4,5,6]
               ^

Now continue the loop:

your_list = [3,4,5,6]
                 ^

Now pop off first item:

your_list = [4,5,6]
                 ^

Now continue the loop -- Wait, we're done. :-)

---

>>> l = [1,2,3,4,5,6]
>>> for x in l:
...     l.pop(0)
... 
1
2
3
>>> print l
[4, 5, 6]

这篇关于为什么带有 pop 方法(或 del 语句)的 for 循环不遍历所有列表元素的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！