You can use the + operator for lists also. It works like .extend but creates a new list and leaves the original lists unchanged.

list1 = [1, 2, 3]

list2 = [4, 5]

list3 = list1 + list2

list3 is [1, 2, 3, 4, 5]

list1 is still [1, 2, 3] and list2 is still [4, 5]

The += operator works the exact same as .extend. It adds a list to the end of the list, altering the first list but not the second.