Send keys to the device.

def send_keys(self, keys):
        """Send keys to the device."""
        try:
            sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            sock.settimeout(self._timeout)
            sock.connect((self._ip, self._port['cmd']))
            # mandatory dance
            version_info = sock.recv(15)
            sock.send(version_info)
            sock.recv(2)
            sock.send(bytes.fromhex('01'))
            sock.recv(4)
            sock.recv(24)
            # send our command now!
            for key in keys:
                if key in self._keys:
                    sock.send(bytes.fromhex("04 01 00 00 00 00 " +
                                            self._keys[key]))
                    sock.send(bytes.fromhex("04 00 00 00 00 00 " +
                                            self._keys[key]))
            sock.close()
        except socket.error:
            raise