def list_diff(l1: list, l2: list):
    """ Return a list of elements that are present in l1
        or in l2 but not in both l1 & l2.
        IE: list_diff([1, 2, 3, 4], [2,4]) => [1, 3]
    """
    return [i for i in l1 + l2 if i not in l1 or i not in l2]