code: def _delete_objects_not_in_list(self, cont, object_prefix=""):
          
          objnames = set(cont.get_object_names(prefix=object_prefix,
                  full_listing=True))
          localnames = set(self._local_files)
          to_delete = list(objnames.difference(localnames))
          self._sync_summary["deleted"] += len(to_delete)
          # We don't need to wait around for this to complete. Store the thread
          # reference in case it is needed at some point.
          self._thread = self.bulk_delete(cont, to_delete, async_=True)
docs: Finds all the objects in the specified container that are not present
          in the self._local_files list, and deletes them.