如何使PyQt5中的菜单栏具有初始焦点？

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

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

        menubar = self.menuBar()
        file_menu = menubar.addMenu('File')
        edit_menu = menubar.addMenu('Edit')

        # 添加菜单项
        file_menu.addAction('New')
        file_menu.addAction('Open')
        file_menu.addAction('Save')
        edit_menu.addAction('Cut')
        edit_menu.addAction('Copy')
        edit_menu.addAction('Paste')

        # 设置菜单栏的焦点
        menubar.setFocusPolicy(Qt.StrongFocus)

if __name__ == '__main__':
    app = QApplication([])
    window = MainWindow()
    window.show()
    app.exec_()