How to close serial port when closing window with pyqt5

Question

This code reads the output of the arduino fine and live plots the values. But when I close the window, the serial connection doesn't close.

import pyqtgraph as pg
from PyQt5 import QtCore, QtWidgets, QtSerialPort
import sys

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        self.graphWidget = pg.PlotWidget()
        self.setCentralWidget(self.graphWidget)

        self.x = list(range(100))  
        self.y = [0 for _ in range(100)] 

        self.graphWidget.setBackground('w')

        pen = pg.mkPen(color=(255, 0, 0))
        self.data_line =  self.graphWidget.plot(self.x, self.y, pen=pen)

        self.serial_port = QtSerialPort.QSerialPort("COM3")
        self.serial_port.setBaudRate(QtSerialPort.QSerialPort.Baud9600)
        self.serial_port.errorOccurred.connect(self.handle_error)
        self.serial_port.readyRead.connect(self.handle_ready_read)
        self.serial_port.open(QtCore.QIODevice.ReadWrite)

    def handle_ready_read(self):
        while self.serial_port.canReadLine():
            codec = QtCore.QTextCodec.codecForName("UTF-8")
            line = codec.toUnicode(self.serial_port.readLine()).strip().strip('\x00')
            try:
                print(line)
                value = float(line)
            except ValueError as e:
                print("error", e)
            else:
                self.update_plot(value)


    def handle_error(self, error):
        if error == QtSerialPort.QSerialPort.NoError:
            return
        print(error, self.serial_port.errorString())

    def update_plot(self, value):
        self.y = self.y[1:] + [value]
        self.x = self.x[1:]  
        self.x.append(self.x[-1] + 1)  
        self.data_line.setData(self.x, self.y) 

app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
w.show()

app.exec_()
    

How do I make sure the serial port closes when the window is closed? Maybe a button to close it on the window would be a better idea.

If I put serial_port = QtSerialPort.QSerialPort("COM3") outside the main window (then put self.serial_port = serial_port inside the main window init), then I can put serial_port.close() at the end of the file. But I don't know if this could cause problems trying some things if the serial port connection wasn't initialized in the main window.

Answer 1

If you want to terminate the connection when the window closes then do it in the closeEvent method:

class MainWindow(QtWidgets.QMainWindow):
    # ...
    def closeEvent(self, event):
        super(MainWindow, self).closeEvent(event)
        self.serial_port.close()