input: Write a python function to return a list of unique elements from the given list.
  assert unique_list([1, 2, 2, 3, 4, 4, 5]) == [1, 2, 3, 4, 5]
  assert unique_list([10, 10, 20, 20, 30, 30]) == [10, 20, 30]
  assert unique_list([5, 5, 5, 5, 5]) == [5]
output: def unique_list(lst):
      return list(set(lst))