为什么使用pop-method（或del语句）的for-loop不能迭代所有列表元素 [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，尝试使用列表
我正在使用Python 3.2.3（默认，2012年10月19日，20:13:42），Linux2上的[GCC 4.6.3]

以下是我的示例代码

 >>> l = [1,2,3,4,5,6] 
>>> （l）
 ... 
  

我期望以下输出

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

相反，我得到这个

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

for循环在3转之后停止迭代。有人可以解释一下为什么吗？解决方案展开一点（脱字符（ ^ ） >）在循环index）：

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

弹出第一项后：

  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：
 
 $ p $  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。 ： - ）

---

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

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