Cloning Lists¶

If we want to modify a list and also keep a copy of the original, we need to be able to make a copy of the list itself, not just the reference. This process is sometimes called cloning, to avoid the ambiguity of the word copy.

The easiest way to clone a list is to use the slice operator.

Taking any slice of a creates a new list. In this case the slice happens to consist of the whole list.

(chp09_is4)

Now we are free to make changes to b without worrying about a. Again, we can clearly see in codelens that a and b are entirely different list objects.

Check your understanding

rec-5-1: What is printed by the following statements?

alist = [4,2,8,6,5]
blist = alist * 2
blist[3] = 999
print(alist)

[4,2,8,999,5,4,2,8,6,5]
print alist not print blist
[4,2,8,999,5]
blist is changed, not alist.
[4,2,8,6,5]
Yes, alist was unchanged by the assignment statement. blist was a copy of the references in alist.