python save_screenshot()保存一直失败

    def screen_shot(self):
        """截图"""
        print('截图')
        shot_name = datetime.now().strftime("%Y-%m-%d_%H:%M:%S")
        shot_name = os.path.join(p_path.SCREEN_SHOT_PATH, shot_name + '.png')
        picture_url = self.driver.save_screenshot(shot_name)