code: def notes_slide(self):
          
          try:
              notes_slide_part = self.part_related_by(RT.NOTES_SLIDE)
          except KeyError:
              notes_slide_part = self._add_notes_slide_part()
          return notes_slide_part.notes_slide
docs: The |NotesSlide| instance associated with this slide. If the slide
          does not have a notes slide, a new one is created. The same single
          instance is returned on each call.