code: def _load_sensors(self, path=None):
          
          if path is None:
              path = self.persistence_file
          exists = os.path.isfile(path)
          if exists and os.access(path, os.R_OK):
              if path == self.persistence_bak:
                  os.rename(path, self.persistence_file)
                  path = self.persistence_file
              _LOGGER.debug('Loading sensors from persistence file %s', path)
              self._perform_file_action(path, 'load')
              return True
          _LOGGER.warning('File does not exist or is not readable: %s', path)
          return False
docs: Load sensors from file.