code: def set_comment(self, comment = None):
          
          
          if comment is None or type(comment) is not str:
              raise KPError("Need a new image number")
          else:
              self.comment = comment
              self.last_mod = datetime.now().replace(microsecond=0)
              return True
docs: This method is used to the the comment.
  
          comment must be a string.