input: def get_max_value(numbers):
      """
      Return the largest value from a given list of numbers.
      >>> get_max_value([2, 4, 1, 6])
      6
      >>> get_max_value([-1, -5, -3, -2])
      -1
      >>> get_max_value([0, 0, 0, 0])
      0
      """
      return max(numbers)
output:     if not numbers:
          return None