Question

I have a list that I add items to as the program runs and I have created a copy of this list so I can change/modify/examine the copy WITHOUT changing the original.

This is what I’ve got so far:

import copy
originallist.append(stuff)

combined=''.join(originallist)

copyoriginal=copy.deepcopy(originallist) 
##this didnt work as copyoriginal stayed empty [] while originallist would change.
#i also tried 
copyoriginal=list(originallist) 
#AND 
copyoriginal=originallist[:] 
#and with both cases copyoriginal remained at [] while originallist would change!!

Why does it not change?

Answer 1

If you want to “keep up with changes” to another list, you may want to consider using a simple reference instead of a copy:

a = [1, 2, 3]
b = a # b refers to a

a[0] = 3
print b # prints [3, 2, 3]

You can always make a copy later when you decide you want to stop tracking changes:

b = b[:]