The code below uses unittest to run. It creates a new WebDriver object and users it to fetch http://twitter.com and submit a username and password. Once the details are added it “clicks” the “Sign In” button to login into Twitter.

#!/usr/bin/env python

import unittest
import logging
from webdriver_firefox.webdriver import FirefoxLauncher
from webdriver_firefox.webdriver import WebDriver

class TwitterTests (unittest.TestCase):

    def test_login_twitter(self):
        driver = WebDriver()
        driver.get("http://twitter.com")

        # find our elements - the html on the page with same ids
        username_element = driver.find_element_by_id('username')
        password_element = driver.find_element_by_id('password')

        # use this to toggle the remember me box
        remember_me_element = driver.find_element_by_id('remember')

        # type into the boxes
        username_element.send_keys('yourusername')
        password_element.send_keys('yourpassword')
        remember_me_element.toggle()

        # click Sign In and we should be logged in
        driver.find_element_by_id('signin_submit').click()

       # check that the title of the page is correct to see if we logged in
        self.assertEqual(driver.get_title(), 'Twitter / Home')

        # Extract from the html using xpath to find username and updates of the people on the screen
        updates = driver.find_elements_by_xpath("//span[@class='entry-content']");
        user = driver.find_elements_by_xpath("//a[@class='screen-name']");

        # display in the terminal the name and the update
        for i,update in enumerate(updates):
            print user[i].get_text() + ": " +update.get_text()

        # uncomment the following to close the window and finish
        #driver.quit()

if __name__ == "__main__":
    logging.basicConfig(level=logging.INFO)
    unittest.main()

The docs are not great for WebDriver but reading the source is pretty simple. Being able to mentally parse Java to Python is also a big advantage!