code: def close(self):
          
          if self._closed:
              raise err.Error("Already closed")
          self._closed = True
          if self._sock is None:
              return
          send_data = struct.pack('<iB', 1, COMMAND.COM_QUIT)
          try:
              self._write_bytes(send_data)
          except Exception:
              pass
          finally:
              self._force_close()
docs: Send the quit message and close the socket.
  
          See `Connection.close() <https://www.python.org/dev/peps/pep-0249/#Connection.close>`_
          in the specification.
  
          :raise Error: If the connection is already closed.