Extracting from a list

[Joel Bender]

Hi,


I would like to process the elements of a list that match a condition, 
then remove them.  I'll use integers in my example, but my list items 
are actually objects.

What's the "right" way to do this?  For example:

    >>> lst = [3, 2, 5, 1, 0, 7, 4, 8, 6, 9]
    >>> dothese = [i for i in lst if i < 5]
    >>> lst = [i for i in lst if i >= 5]
    >>> for item in dothese:
    ...     print item

I'd rather not scan the list twice, particularly if there's nothing to 
do.  I'd rather not build another double-linked list.

Is there something like this?

    >>> for item in lst:
    ...     if (item < 5):
    ...         print item
    ...         del lst[ xxxx ]

But the "trick" is figuring out what xxxx should be.  Using lst.remove() 
would work if the internals used "is" and not "is equal to" and the 
removal didn't modify the list where it would break the loop somehow.

I could rebuild the list for things that should not be processed:

    >>> newlst = []
    >>> for item in lst:
    ...     if (item < 5):
    ...         print item
    ...     else
    ...         newlst.append(item)
    >>> lst = newlst

But these seems like a lot of work when there's nothing in the list to 
process.


Joel