tests.py

 def login(self, driver):
        """
        This method is internal to testing framework
        It is used to login the user.
        Each test requires the user to be logged in already
        Parameters:
            driver - reference to driver being used
        """
        # this is the tricky part
        # We have to get the right handle for the correct popup login window
        main_window_handle = driver.current_window_handle

        driver.find_element_by_id('signin').click()

        signin_window_handle = None

        # iterating through all the handles to get the popup, since we only hve
        # one popup, making use of that
        while not signin_window_handle:
            for handle in driver.window_handles:
                if handle != main_window_handle:
                    signin_window_handle = handle
                    break

        # switch to the signin popup
        driver.switch_to.window(signin_window_handle)

        wait = WebDriverWait(driver, 60)

        email_field = wait.until(
            EC.element_to_be_clickable((By.ID, "authentication_email")))

        # this is the example user from mockmyid
        email_field.send_keys("helloworld@mockmyid.com")

        # xpath id obtained using firebug for the next button on persona dialog
        (driver.find_element_by_xpath(
            "/html/body/div/section[1]/form/div[2]/div[1]/div/div[2]/p[4]/button[1]")
            .click())

        # switch to the main window
        driver.switch_to.window(main_window_handle)