input: Write a function to identify the second lowest value in an array.
  assert second_lowest([1, 2, -8, -2, 0, -2]) == -2
  assert second_lowest([1, 1, -0.5, 0, 2, -2, -2]) == -0.5
  assert second_lowest([2, 2]) == None
output: def second_lowest(arr):
      unique_values = list(set(arr))
      if len(unique_values) < 2:
          return None
      unique_values.sort()
      return unique_values[1]