Removing items from a list

MRAB python at mrabarnett.plus.com
Fri Feb 10 21:26:26 CET 2012


On 10/02/2012 20:04, Thomas Philips wrote:
> In the past, when deleting items from a list, I looped through the
> list in reverse to avoid accidentally deleting items I wanted to keep.
> I tried something different today, and, to my surprise, was able to
> delete items correctly, regardless of the direction in which I looped,
> in both Python 3.2.2. and 2..1 -  does the remove() function somehow
> allow the iteration to continue correctly even when items are removed
> from the midde of the list?
>
>>>>  x = list(range(10))
>>>>  x
> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>>>  for i in x:
> 	if i % 2 == 0:
> 		x.remove(i)
>
>>>>  x
> [1, 3, 5, 7, 9]
>>>>  for i in reversed(x):
> 	if i % 2 == 0:
> 		x.remove(i)
>
>>>>  x
> [1, 3, 5, 7, 9]
>>>>  x = list(range(10))
>>>>  for i in reversed(x):
> 	if i % 2 == 0:
> 		x.remove(i)
>
>
>>>>  x
> [1, 3, 5, 7, 9]
>
The answer is no. For example:

 >>> for i in x:
	print("i is", i)
	if i % 2 == 0:
		x.remove(i)

		
i is 0
i is 1
i is 2
i is 4
 >>> x
[0, 1, 3, 5]



More information about the Python-list mailing list