get_screenshot_as_file()方法在存在alert弹窗时报错问题

用python做selenium自动化时，截图出现了错误，奇怪的是正确的用户和密码截图没问题，错误的用户名和密码登录失败出现alert弹窗时截图就报错，真的奇怪，记录一下

from ddt import ddt, data, unpack
from base.browser_engine import BrowserEngine
import unittest
from common.excel_util import ExcelUtil
from pageobjects.baiyueSMS_homepage import BaiYueSMSPage
from base.logger import Logger

logger = Logger(logger='test_login').get_log()


@ddt
class TestLogin(unittest.TestCase):
    driver = None

    def setUp(self):
        self.driver = BrowserEngine().open_browser()

    def tearDown(self):
        self.driver.quit()

    @data(*ExcelUtil().read_excel())
    @unpack
    def test_login_case001(self, index, username, passwd):
        baiyuesms_homepage = BaiYueSMSPage(self.driver)
        baiyuesms_homepage.login_sms(username, passwd)
        baiyuesms_homepage.get_windows_img()
        if index == 1:
            self.assertEqual(baiyuesms_homepage.get_expect_result(), '管理员')
        elif index == 2:
            self.assertEqual(baiyuesms_homepage.get_text(), '登录失败 : 用户名或者密码错误')
        elif index == 3:
            self.assertEqual(baiyuesms_homepage.get_text(), '登录失败 : 用户名或者密码错误')


if __name__ == '__main__':
    unittest.main()

    def get_windows_img(self):
        file_path = PathUtil().get_path() + '\\screenshots\\'
        rq = time.strftime('%Y%m%d%H%M%S', time.localtime(time.time()))
        screen_name = file_path + rq + '.png'
        try:
            self.driver.get_screenshot_as_file(screen_name)
            logger.info('开始截图并保存')
        except Exception as e:
            logger.error('截图异常', format(e))

进行单独方法的测试也报错了