如何在python pyqt5中主窗口管理第二个窗口

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton, QDialog

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

    def initUI(self):
        self.setWindowTitle("主窗口")

        self.button = QPushButton("打开第二个窗口", self)
        self.button.clicked.connect(self.openSecondWindow)
        self.button.setGeometry(50, 50, 200, 30)

    def openSecondWindow(self):
        self.secondWindow = SecondWindow()
        self.secondWindow.show()

class SecondWindow(QDialog):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        self.setWindowTitle("第二个窗口")
        self.setGeometry(200, 200, 300, 200)

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