input: Write a function to calculate the maximum, minimum, and mean number of elements in a given string. The function should return a tuple containing the maximum element, minimum element, and the mean value of the elements in the string. If the string is empty, it should return `(None, None, None)`.
  
  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 if num_elements > 0 else 0
      return (max_element, min_element, mean_element)
  
  assert get_stats_for_string("abcdef") == ('f', 'a', 100.0)
  assert get_stats_for_string("") == (None, None, None)
  assert get_stats_for_string("abbccc") == ('c', 'a', 97.83333333333333)
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 if num_elements > 0 else 0
      return (max_element, min_element, mean_element)