PyQt5 Quit button

Question

Could you please explain why the quit push button does not work properly in this case:

import sys
from PyQt5.QtWidgets import QWidget, QPushButton, QApplication
from PyQt5.QtCore import QCoreApplication


class Example(QWidget):

    def __init__(self):
        super().__init__()       
        self.initUI()


    def initUI(self):               
        qbtn = QPushButton('Quit', self)
        qbtn.clicked.connect(QCoreApplication.instance().quit)
        qbtn.move(50, 50)       
        self.setGeometry(300, 300, 250, 150)   
        self.show()


app = QApplication(sys.argv)
ex = Example()
sys.exit(app.exec_())

But works if I include the last three lines in a function:

def fun():
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

fun()

I don't understand the mechanics :(

Answer 1

I ran into the same problem while using linux. This code comes from a tutorial on zetcode.com for PyQt5 in the quitButton.py file. Here is the solution that I found works:

Instead of using:

qbtn.clicked.connect(QCoreApplication.instance().quit)

Replace it with this:

qbtn.clicked.connect(self.close)

After this, you shouldn't need to call it in a separate function. Hope this helps!

Answer 2

I tried this recently. I need a sure exit from within spyder and this always seems a problem with pyqt. I found qbtn.clicked.connect(QCoreApplication.instance().quit) will quit and leave window open. qbtn.clicked.connect(self.close) will close the window but leave the process running. qbtn.clicked.connect(QCoreApplication.instance().quit) qbtn.clicked.connect(self.close) sequentially will quit and close window. This is pyqt5 on Python 3.8.8. Hope this is helpful.