python pyqt5 多文档窗体

def __init__(self, parent=None):
    super(MainWindow, self).__init__(parent)
    self.mdi = QMdiArea()
    self.setCentralWidget(self.mdi)
    bar = self.menuBar()
    file = bar.addMenu("File")
    file.addAction("New")
    file.addAction("cascade")
    file.addAction("Tiled")
    file.triggered[QAction].connect(self.windowaction)
    self.setWindowTitle("MDI demo")

def windowaction(self, q):
    print("triggered")

    if q.text() == "New":
        MainWindow.count = MainWindow.count + 1
        sub = QMdiSubWindow()
        sub.setWidget(QTextEdit())
        sub.setWindowTitle("subwindow" + str(MainWindow.count))
        self.mdi.addSubWindow(sub)
        sub.show()
    if q.text() == "cascade":
        self.mdi.cascadeSubWindows()
    if q.text() == "Tiled":
        self.mdi.tileSubWindows()