code: def save_sensors(self):
          
          if not self.need_save:
              return
          fname = os.path.realpath(self.persistence_file)
          exists = os.path.isfile(fname)
          dirname = os.path.dirname(fname)
          if (not os.access(dirname, os.W_OK) or exists and
                  not os.access(fname, os.W_OK)):
              _LOGGER.error('Permission denied when writing to %s', fname)
              return
          split_fname = os.path.splitext(fname)
          tmp_fname = '{}.tmp{}'.format(split_fname[0], split_fname[1])
          _LOGGER.debug('Saving sensors to persistence file %s', fname)
          self._perform_file_action(tmp_fname, 'save')
          if exists:
              os.rename(fname, self.persistence_bak)
          os.rename(tmp_fname, fname)
          if exists:
              os.remove(self.persistence_bak)
          self.need_save = False
docs: Save sensors to file.