title: Convert Date String to Day of Week
body: <p>I have date strings like this:</p>
  
  <pre><code>'January 11, 2010'
  </code></pre>
  
  <p>and I need a function that returns the day of the week, like</p>
  
  <pre><code>'mon', or 'monday'
  </code></pre>
  
  <p>etc.
  I can't find this anywhere in the Python help.
  Anyone? Thanks.</p>