Write a function named num_unique_values that accepts a list of integers as a parameter and returns the number of unique integer values in the list. For example, if a list named l contains the values [3, 7, 3, -1, 2, 3, 7, 2, 15, 15], the call of num_unique_values(l) should return 5. If passed the empty list, you should return 0. Use a set as auxiliary storage to help you solve this problem. Do not modify the list passed in. With python