docs: def unit(v, lg=1):
      """ unit vector
      Args:
          v: vector (x, y)
          lg: length
      Raises:
          ValueError: Null vector was given
      """
      try:
          res = scale(v, lg / distance((0, 0), v))
      except ZeroDivisionError:
          raise ValueError("Null vector was given")
      return res