If I have a list x = [1,2,3,4,5,6,7,8,9] and another list that is a subset of x: y = [1,4,7] , is there a quick way that I could return the complementary subset to y.... z=[2,3,5,6,8,9] ? The reason I ask is because I have a generator function that generates a list of tuples and I would like to divide this list into complementary lists.