>>> def s(s_list):
... s_list += [47,11]
... print(s_list)
...
>>> fib = [0,1,1,2,3,5,8]
>>> s(fib[:])
[0, 1, 1, 2, 3, 5, 8, 47, 11]
>>> fib
[0, 1, 1, 2, 3, 5, 8]
The Slice Operator creates a copy of the list, i.e. fib[:] copies the complete list. This copy is passed on to the function with s(fib).