code: def _on_file_deleted(self, event: FileSystemEvent):
          
          if not event.is_directory and self.is_data_file(event.src_path):
              assert event.src_path in self._origin_mapped_data
              del(self._origin_mapped_data[event.src_path])
              self.notify_listeners(FileSystemChange.DELETE)
docs: Called when a file in the monitored directory has been deleted.
          :param event: the file system event