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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def close(self):
 """ 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. """

        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()