160         assert self._open is None

   160         assert self._open is None

   161         self._open = True

   161         self._open = True

   162         self._cnx = self._session.new_cnx()

   162         self._cnx = self._session.new_cnx()

   163         self._cnx.__enter__()

   163         self._cnx.__enter__()

   164         self._cnx.ctx_count += 1

   164         self._cnx.ctx_count += 1

   165 

   166 

   166     def __exit__(self, exc_type, exc_val, exc_tb):

   167     def __exit__(self, exc_type, exc_val, exc_tb):

   167         self._open = False

   168         self._open = False

   168         self._cnx.ctx_count -= 1

   169         self._cnx.ctx_count -= 1

   169         self._cnx.__exit__(exc_type, exc_val, exc_tb)

   170         self._cnx.__exit__(exc_type, exc_val, exc_tb)