input: Write a function to calculate the maximum, minimum, and mean number of elements in a given string. If the string is empty, return (None, None, None). Otherwise, return a tuple with the maximum element, minimum element, and mean value of the ASCII values of the characters in the string.
  
  
  def get_stats_for_string(string):
      if not string:
          return (None, None, None)
      num_elements = len(string)
      ascii_values = [ord(char) for char in string]
      max_element = max(ascii_values)
      min_element = min(ascii_values)
      mean_element = sum(ascii_values) / num_elements
      return (max_element, min_element, mean_element)
  
  assert get_stats_for_string("abcdef") == (102, 97, 99.5)
  assert get_stats_for_string("xyz") == (122, 120, 121.0)
  assert get_stats_for_string("") == (None, None, None)
  
output: 
  def get_stats_for_string(string):
      if not string:
          return (None, None, None)
      num_elements = len(string)
      ascii_values = [ord(char) for char in string]
      max_element = max(ascii_values)
      min_element = min(ascii_values)
      mean_element = sum(ascii_values) / num_elements
      return (max_element, min_element, mean_element)
  