PyQt5对话框关闭主窗口

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QMessageBox

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("Main Window")

    def closeEvent(self, event):
        reply = QMessageBox.question(self, '确认关闭', '确定要关闭应用程序吗？',
                                     QMessageBox.Yes | QMessageBox.No, QMessageBox.No)
        if reply == QMessageBox.Yes:
            event.accept()
        else:
            event.ignore()

if __name__ == '__main__':
    app = QApplication(sys.argv)
    mainWindow = MainWindow()
    mainWindow.show()
    sys.exit(app.exec_())