title: What is the order of evaluation in python when using pop(), list[-1] and +=?
body: <pre><code>a = [1, 2, 3]
  a[-1] += a.pop()
  </code></pre>
  
  <p>This results in <code>[1, 6]</code>.</p>
  
  <pre><code>a = [1, 2, 3]
  a[0] += a.pop()
  </code></pre>
  
  <p>This results in <code>[4, 2]</code>. What order of evaluation gives these two results?</p>