title: Using double square brackets?
body: <p>In a file using an older version of Python, I found the following piece of code:</p>
  
  <pre><code>PROP_UI_COMBO = 'Prop_UI_ComboBox'
  PROP_UI_COMBO[[]] = [_[1], [x for x in range(-1, 10)] + [26, 28, 30]]
  </code></pre>
  
  <p>And I'm wondering what it means to set <code>PROP_UI_COMBO[[]]</code>. What do the double brackets mean?
  Also, (I may be wrong) I believe that <code>_[1]</code> is just the temporary list of <code>[x for x in range(-1, 10)]</code>. So as my question presents, what is the <code>[[]]</code> for, and what is the equivalent in Python 3.4?</p>