input: Write a function to calculate the maximum, minimum, and mean of the elements in a given string. The function should return these values in a tuple.
  
  def get_stats_for_string(string):
      num_elements = len(string)
      max_element = max(string)
      min_element = min(string)
      mean_element = sum(string) / num_elements
      return (max_element, min_element, mean_element)
      
  assert get_stats_for_string("abcdef")==('f', 'a', 3.5)
  assert get_stats_for_string("12345")==('5', '1', 3.0)
  assert get_stats_for_string("")==(None, None, None)
  assert get_stats_for_string("zzzz")==('z', 'z', 122.5)
output: def get_stats_for_string(string):
      if not string:
          return (None, None, None)
      num_elements = len(string)
      max_element = max(string)
      min_element = min(string)
      mean_element = sum(ord(char) for char in string) / num_elements
      return (max_element, min_element, mean_element)