按钮pyqt5后无法打开新窗口

from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton, QWidget

class NewWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("New Window")
        self.setGeometry(100, 100, 300, 200)

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("Main Window")
        self.setGeometry(100, 100, 300, 200)

        button = QPushButton("Open New Window", self)
        button.setGeometry(100, 100, 150, 30)
        button.clicked.connect(self.open_new_window)

    def open_new_window(self):
        new_window = NewWindow()
        new_window.show()

if __name__ == "__main__":
    app = QApplication([])
    main_window = MainWindow()
    main_window.show()
    app.exec_()