diff list by set

def list_diff(list_a, list_b):
    set_a = set(list_a)
    set_b = set(list_b)
    set_int = set_a.intersection(set_b)
    gone_items = set_a - set_int
    new_items = set_b - set_int
    return {'---':list(gone_items),
            '+++':list(new_items)}

def list_diff(list_a, list_b):
    set_a = set(list_a)
    set_b = set(list_b)
    set_int = set_a.intersection(set_b)
    return {'---':list(set_a - set_int),
            '===':list(set_int),
            '+++':list(set_b - set_int)}