如何从PyQT5的菜单中调用新的(弹出)窗口？

from PyQt5.QtWidgets import QApplication, QMainWindow, QAction, QDialog

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        # 创建菜单栏
        menubar = self.menuBar()
        fileMenu = menubar.addMenu('文件')

        # 创建菜单项
        newAction = QAction('新建', self)
        newAction.triggered.connect(self.openNewWindow)
        fileMenu.addAction(newAction)

    def openNewWindow(self):
        # 创建新的弹出窗口
        dialog = QDialog(self)
        dialog.setWindowTitle('新窗口')
        dialog.exec_()

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