As per the error, you are trying to add a list to a string. Python cannot add them and hence it's giving the error.
i[-1] is the last element of your list, which is 'y' and i[:-1] is a list. If you want to put the last element in the first position in your new list, you can do the following:
>>> id = [i[-1]] + i[:-1] #Add [] to make it a list
>>> id
['y', 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]