code: def clear(self):
          
          # mark this task as incomplete
          self.mark_incomplete()
  
          # Delete the indicator metadata, this also deletes values by cascading.
          #
          # NOTE: calling 'delete()' on the query (instead of on the queried object,
          # as done here), would NOT work! For a query, there is no in-Python cascading
          # of delete statements in sqlalchemy, so the associated values would not
          # be deleted e.g. for SQLite databases.
          try:
              indicator = self.session.query(models.EuroStatIndicator) \
                  .filter(models.EuroStatIndicator.number == self.number) \
                  .one()
              self.session.delete(indicator)
          except NoResultFound:
              # Data didn't exist yet, no problem
              pass
  
          self.close_session()
docs: Clear output from one (derived) class loader