title: Invalid format string in Python
body: <p>I get the invalid format string error when I try to run the below code (last line), not sure where I am missing the point:</p>
  
  <pre><code>  import datetime
    DAYS = 2
    SINCE = datetime.datetime.now() - datetime.timedelta(days=DAYS)
    params = "?fields=feed.since(" + SINCE.strftime("%s") + ").limit(1),name,updated_time&amp;amp;"
  </code></pre>
  
  <p>Any suggestions would be much appreciated !!</p>