Does updating the list take extra space?

Question

I have an array or list, Now I want to make some changes in the array and put in back to the arr variable/list. Am I using extra space? or it is the same variable gets updated again?

arr = [1,2,3,4]
print arr[2:] + arr[:2] # Is is using extra space
#or
arr = arr[2:] + arr[:2] # Is is using extra space
#or
arr = [1,2,3,4]
arr = arr # are not they both same? LHS arr is different from RHS arr

Answer 1

when assigning like this:

arr = arr[2:] + arr[:2]

you're creating a new reference of arr, and the old one is destroyed. Means allocation/deletion.

You should do slice assignment:

arr[:] = arr[2:] + arr[:2]

arr keeps the same reference, and if the size doesn't change, no memory allocaton occurs for arr (but the right hand side sum & slicing still needs allocation)

Demo:

arr = [1,2,3,4]
old_arr = arr
arr = arr[2:] + arr[:2]
print(old_arr is arr)

result: False

arr = [1,2,3,4]
old_arr = arr
arr[:] = arr[2:] + arr[:2]
print(old_arr is arr)

result: True