title: Grab username:password from text file, then post into login form
body: <p>I have a text file with usernames and passwords. The text file is formatted like this:</p>
  
  <pre><code>username1:password1
  username2:password2
  username3:password3
  </code></pre>
  
  <p>I want to grab the first line, split it to "username1" and "password1", and then post to this:</p>
  
  <pre><code>br.form['login'] = 'username1'
  br.form['passwd'] = 'password1'
  </code></pre>
  
  <p>After that, I want it to repeat and move onto username2:password2.</p>
  
  <p>How can this be done?</p>