Write a function that takes in an array of unique integers and returns its powerset. The powerset P(X) of a set X is the set of all subsets of X. For example, the powerset of [1,2] is [[], [1], [2], [1,2]]. Note that the sets in the powerset do not need to be in any particular order.
Sample input: [1, 2, 3]
Sample output: [[], [1], [2], [3], [1, 2], [1, 3], [2, 3], [1, 2, 3]]
Check this Python code.