python - Why does a for-loop with pop-method (or del statement) not iterate over all list elements

Question

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?

Answer 1

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]