docs: def _open_connection(self):
          """Open a connection to the easyfire unit."""
          if (self._mode == PROP_MODE_SERIAL):
              self._serial = serial.Serial(self._serial_device, self._serial_speed)
          elif (self._mode == PROP_MODE_TCP):
              self._socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
              self._socket.connect((self._ip, self._port))
          elif (self._mode == PROP_MODE_FILE):
              self._file = open(self._file_path, "r")