code: def shutdown(self):
          
          with self._lock:
              if self.is_shutdown:
                  return
              else:
                  self.is_shutdown = True
  
          # PYTHON-673. If shutdown was called shortly after session init, avoid
          # a race by cancelling any initial connection attempts haven't started,
          # then blocking on any that have.
          for future in self._initial_connect_futures:
              future.cancel()
          wait_futures(self._initial_connect_futures)
  
          for pool in tuple(self._pools.values()):
              pool.shutdown()
docs: Close all connections.  ``Session`` instances should not be used
          for any purpose after being shutdown.