PyQt5 QThread Process finished with exit code 139 (interrupted by signal 11: SIGSEGV)

Question

i have a GUI with PyQt5. The GUI has a Form, 2 Buttons and a ProgressBar. I want to implement a start/wait thread with QThread. Unfortunately i get Process finished with exit code 139 (interrupted by signal 11: SIGSEGV) when i click Start button to run thread.

MainWindow.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'MainWindow.ui'
#
# Created by: PyQt5 UI code generator 5.15.4
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName("Form")
        Form.resize(400, 138)
        self.btnRun = QtWidgets.QPushButton(Form)
        self.btnRun.setGeometry(QtCore.QRect(20, 20, 89, 25))
        self.btnRun.setObjectName("btnRun")
        self.btnStop = QtWidgets.QPushButton(Form)
        self.btnStop.setGeometry(QtCore.QRect(20, 60, 89, 25))
        self.btnStop.setObjectName("btnStop")
        self.progressBar = QtWidgets.QProgressBar(Form)
        self.progressBar.setGeometry(QtCore.QRect(20, 100, 371, 23))
        self.progressBar.setProperty("value", 24)
        self.progressBar.setObjectName("progressBar")

        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)

    def retranslateUi(self, Form):
        _translate = QtCore.QCoreApplication.translate
        Form.setWindowTitle(_translate("Form", "Test Thread"))
        self.btnRun.setText(_translate("Form", "Run"))
        self.btnStop.setText(_translate("Form", "Stop"))

When i click the Start button the application crashes with segmentation fault.

Thread.py

from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
from MainWindow import *
import sys
import time

class MainWindow(QWidget, QThread):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.ui = Ui_Form()
        self.ui.setupUi(self)
        self.center()
        #Init progressBar
        self.ui.progressBar.setValue(0)
        #Buttons
        self.ui.btnRun.clicked.connect(self.start)
        self.ui.btnStop.clicked.connect(self.wait)

    def run(self):
        count = 0
        while count <= 100:
            count += 1
            self.ui.progressBar.setValue(count)
            time.sleep(1)

    def center(self):
        # geometry of the main window
        qr = self.frameGeometry()

        # center point of screen
        cp = QDesktopWidget().availableGeometry().center()

        # move rectangle's center point to screen's center point
        qr.moveCenter(cp)

        # top left of rectangle becomes top left of window centering it
        self.move(qr.topLeft())



if __name__ == '__main__':
    app = QApplication(sys.argv)
    app.setAttribute(Qt.AA_DontShowIconsInMenus, False)
    w = MainWindow()
    #   Disable maximize window button
    w.setWindowFlags(Qt.WindowCloseButtonHint | Qt.WindowMinimizeButtonHint)
    w.show()
    sys.exit(app.exec_())

Answer 1

The problem is that you cannot inherit from QWidget and QThread at the same time because:

• Cannot inherit from 2 QObject, there is a conflict in behaviors.
• PyQt limits multiple inheritance.

The solution is to use composition instead of multiple inheritance.

class Thread(QThread):
    progressChanged = pyqtSignal(int)

    def run(self):
        count = 0
        while count <= 100:
            count += 1
            self.progressChanged.emit(count)
            time.sleep(1)

class MainWindow(QWidget):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.ui = Ui_Form()
        self.ui.setupUi(self)
        self.center()
        self._custom_thread = Thread()
        #Init progressBar
        self.ui.progressBar.setValue(0)
        #Buttons
        self.ui.btnRun.clicked.connect(self._custom_thread.start)
        self.ui.btnStop.clicked.connect(self._custom_thread.wait)

        self._custom_thread.progressChanged.connect(self.ui.progressBar.setValue)