Python용 Selenium에서 새 창으로 전환하는 방법은 무엇입니까?

import unittest
from selenium import webdriver

class GoogleOrgSearch(unittest.TestCase):

    def setUp(self):
        self.driver = webdriver.Firefox()

    def test_google_search_page(self):
        driver = self.driver
        driver.get("http://www.cdot.in")
        window_before = driver.window_handles[0]
        print(window_before)
        driver.find_element_by_xpath("//a[@href='http://www.cdot.in/home.htm']").click()
        window_after = driver.window_handles[1]
        driver.switch_to.window(window_after)
        print(window_after)
        driver.find_element_by_link_text("ATM").click()
        driver.switch_to.window(window_before)

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

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