__author__ = 'Administrator'import sysfrom  PyQt4 import QtGuiclass MessageBox(QtGui.QWidget):    def __init__(self,parent=None):        QtGui.QWidget.__init__(self,parent)        self.setGeometry(300,300,250,150)        self.setWindowTitle('messagebox')    def closeEvent(self, event):        reply=QtGui.QMessageBox.question(self,'Message',                                         'Are you sure to quit?',QtGui.QMessageBox.Yes,                                         QtGui.QMessageBox.No)        if reply==QtGui.QMessageBox.Yes:            event.accept()        else:            event.ignore()app=QtGui.QApplication(sys.argv)qb=MessageBox()qb.show()sys.exit(app.exec_())