title: Variable assignment and modification (in python)
body: <p>When I ran this script (Python v2.6):</p>
  
  <pre><code>a = [1,2]
  b = a
  a.append(3)
  print a
  &gt;&gt;&gt;&gt; [1,2,3]
  print b
  &gt;&gt;&gt;&gt; [1,2,3]
  </code></pre>
  
  <p>I expected <code>print b</code> to output <code>[1,2]</code>. Why did b get changed when all I did was change a? Is b permanently tied to a? If so, can I make them independent? How?</p>