code: def sync(self):
          
          for key_hash, obj in six.iteritems(self._cache):
              # Objects are checked for expiration in __getitem__,
              # but we can check here to avoid unnecessary writes.
              if not obj.has_expired():
                  file_path = self._path_for_hash(key_hash)
                  with open(str(file_path), self._write_mode) as f:
                      obj.dump(f)
docs: Commit deferred writes to file.