import sys
from PyQt5.QtWidgets import QWidget, QMessageBox, QApplication, QLabel, QPushButton
 
class Example(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()
    def initUI(self):
    	ask = QLabel('123',self)
    	ask.move(1,1)
    	btn = QPushButton ('NET',self)
    	self.setGeometry(300, 300, 250, 150)
    	self.setWindowTitle('Message box')
    	self.show()
    def closeEvent(self, event):
        reply = QMessageBox.question(self, 'Message', "Are you sure to quit?", QMessageBox.Yes | QMessageBox.No, QMessageBox.No)
        if reply == QMessageBox.Yes:
            event.accept()
        else:
            event.ignore()        
        
        
if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())