[Tutor] Keeping change-in-place vs. copy methods straight

[Steven D'Aprano]

On Sun, May 04, 2014 at 10:00:08AM +0100, Alan Gauld wrote:

> For the specific case of sort you can always use 
> the sorted() function which does return a reference
> (not a copy!) to the sorted item.

sorted() does make a copy of the list:

py> a = [2, 5, 3, 4, 1]
py> sorted(a), a
([1, 2, 3, 4, 5], [2, 5, 3, 4, 1])

Perhaps you meant that it didn't copy the individual items inside the 
list? If so, you were correct:

py> a = [ [5, 6], [1, 2], [7, 8], [3, 4] ]
py> b = sorted(a)
py> b[0].append(999)
py> a
[[5, 6], [1, 2, 999], [7, 8], [3, 4]]

If you want to make copies of the items, you can import the copy module 
and use copy.deepcopy first.



-- 
Steven