title: Nested brackets empty loop explanation
body: <p>What is the value of <code>x</code> after the following code is executed?</p>
  
  <pre><code>x = []
  for i in range(3):
      x = [x + x]
  
  A.[[[[]]]].
  B.[[[],[]]].
  C.[[[[],[]],[[],[]]]].
  D.[[],[],[],[],[],[]]
  </code></pre>
  
  <p>The answer is <em>c</em>, can someone explain why this happens? I understand the 2/3 iteration, but don't understand how it went from 1st to 2nd, as in why it didn't become <code>[[],[]]</code></p>