DrZhang The function we'll be using, half(), takes a number num as an argument and returns its half with num/2. >>> data = [1,2,3,4,5] >>> def half(num): ... return num/2 ... >>> data_half = [half(i) for i in data] >>> data_half [0.5, 1.0, 1.5, 2.0, 2.5]