title: How to check if a list ONLY contains a certain item
body: <p>I have a list called bag. I want to be able to check if only a particular item is in it.</p>
  
  <pre><code>bag = ["drink"]
  if only "drink" in bag:
      print 'There is only a drink in the bag'
  else:
      print 'There is something else other than a drink in the bag'
  </code></pre>
  
  <p>Of course, where I put 'only' in the code there, it is wrong. Is there any simple replacement of that? I have tried a few similar words.</p>