Python - threading

# --- versiom 1 ---

        self.pushButton.clicked.connect(self.function1)
        QtCore.QMetaObject.connectSlotsByName(Form)
        self.ser = serial.Serial('COM7', 9600, timeout=0,parity = serial.PARITY_NONE)

    def function1(self):
        threading.Thread(target=self.update_text).start()

    def update_text(self):
        s = self.ser.read(10)
        self.textBrowser.append(s.decode())

# --- version 2 ---

        self.update_thread = None # default value at start
        self.pushButton.clicked.connect(self.function1)
        QtCore.QMetaObject.connectSlotsByName(Form)
        self.ser = serial.Serial('COM7', 9600, timeout=0, parity=serial.PARITY_NONE)

    def function1(self):
        # check if thread already run
        if not self.update_thread:
            # run thread
            self.update_thread = threading.Thread(target=self.update_text)
            self.update_thread.start()

    def update_text(self):
        s = self.ser.read(10)
        self.textBrowser.append(s.decode())
        # set None to inform main thread that this thread is over
        self.update_thread = None