shallowcopy of an object

[usercat123]

Can somebody explain to me why in the following code, temp is equal to res after the loop body statement? I have tested it with input [1] and after the loop executes temp is as I said equal to the new res. Also, res = res + temp does not produce the expected [[1],[]] but [[1]].
Can somebody explain this to me as well?

def driver(arr):
    res = [[]]
    def subsets(arr,res):
        if arr == []:
            return
        subsets(arr[1:],res)
        temp = res
        #here temp = [[]] for the inner most function call
        for subset in res:
            subset.append(arr[0])
        #but here temp = res if one tries for instance the input [1]
        res = res + temp
    subsets(arr,res)
    return res