code: def notes_master_part(self):
          
          try:
              return self.part_related_by(RT.NOTES_MASTER)
          except KeyError:
              notes_master_part = NotesMasterPart.create_default(self.package)
              self.relate_to(notes_master_part, RT.NOTES_MASTER)
              return notes_master_part
docs: Return the |NotesMasterPart| object for this presentation. If the
          presentation does not have a notes master, one is created from
          a default template. The same single instance is returned on each
          call.