code: def cleanup_sessions(self, app=None):
          
  
          if not app:
              app = current_app
          for key in app.kvsession_store.keys():
              m = self.key_regex.match(key)
              now = datetime.utcnow()
              if m:
                  # read id
                  sid = SessionID.unserialize(key)
  
                  # remove if expired
                  if sid.has_expired(app.permanent_session_lifetime, now):
                      app.kvsession_store.delete(key)
docs: Removes all expired session from the store.
  
          Periodically, this function can be called to remove sessions from
          the backend store that have expired, as they are not removed
          automatically unless the backend supports time-to-live and has been
          configured appropriately (see :class:`~simplekv.TimeToLiveMixin`).
  
          This function retrieves all session keys, checks they are older than
          :attr:`flask.Flask.permanent_session_lifetime` and if so, removes them.
  
          Note that no distinction is made between non-permanent and permanent
          sessions.
  
          :param app: The app whose sessions should be cleaned up. If ``None``,
                      uses :py:data:`~flask.current_app`.