On Tue, 07 Feb 2006 01:01:43 +1100,
Steven D'Aprano <[EMAIL PROTECTED]> wrote:
> On Mon, 06 Feb 2006 13:35:10 +0000, Steve Holden wrote:
>>> I'm wondering why there is no 'clear' for lists. It feels like a common
>>> operation for mutable containers. :-/
>>>
>> Because it's just as easy to create and assign a new empty list (and
>> have the old unused one garbage collected).
>>
>> l = []
>>
>> is all you need!
> Not so. If that logic were correct, then dicts wouldn't need a clear
> method either, because you could just assign a new empty dict with d = {}.
> But your own sentence tells us why this is not sufficient: because you
> aren't emptying the list, you are reassigning (rebinding) the name. The
> old list still exists, and there is no guarantee that it will be garbage
> collected, because there is no guarantee that it isn't in use somewhere
> else:
> L = [0,1,2]
> D = {"key": L}
> L = [] # rebinds the name L, but the list instance still exists
That is a red herring. Consider this:
L = [object(), object()]
O = L[1]
L = [] # or insert your favorite list-clearing/emptying statement here
What damage is done now that O is still referring to one of the items
that used to be in L?
The trouble begins when references to "the list to which L refers" end
up somewhere else. Then we have to wonder if rebinding L will leave
some other block of code with an outdated list.
Regards,
Dan
--
Dan Sommers
<http://www.tombstonezero.net/dan/>
--
http://mail.python.org/mailman/listinfo/python-list
