Python Forum

Hello,
I would need your help to sort the copy of a list without modifying the initial list.

for example, when I create a copy of the C1 list. Then I sort this copy. Both lists are unfortunately sorted.

def tri_ins(t):
    for k in range(1,len(t)):
        temp=t[k]
        j=k
        while j>0 and temp<t[j-1]:
            t[j]=t[j-1]
            j-=1
            t[j]=temp
    return t

C1=[7,3,6,5,4,2,1]
C2=C1
tri_ins(C2)

I know it's possible using the "sort" function but unfortunately I'm not allow to use it.

C1=[7,3,6,5,4,2,1]
C2=C1
C2=sorted(C1)

Thank you for your help.

The problem is that you are not creating a copy. Lists are mutable, and as a consequence list variables are actually pointers to the lists rather than the lists themselves. So C2 = C1 just makes C2 point to the same list C1 points to. The easiest way to copy a list is with a full list slice (C2 = C1[:]. Note that this is a "shallow" copy. Any lists within the copied lists will still be references to their original list.

C1=[7,3,6,5,4,2,1]
C2=C1

This is just making C2 also point at the same object as C1

To make a new copy of the list use

c2 = c1[:]

or

c2 = list(c1)

oooooh ok...
Thank you very much to both of you!