title: Deepcopy on nested referenced lists created by list multiplication does not work
body: <p>As much as I love Python, the reference and deepcopy stuff sometimes freaks me out.</p>
  
  <p>Why does deepcopy not work here:</p>
  
  <pre><code>&gt;&gt;&gt; import copy
  &gt;&gt;&gt; a = 2*[2*[0]]
  &gt;&gt;&gt; a
  [[0, 0], [0, 0]]
  &gt;&gt;&gt; b = copy.deepcopy(a)
  &gt;&gt;&gt; b[0][0] = 1
  &gt;&gt;&gt; b
  [[1, 0], [1, 0]]     #should be: [[1, 0], [0, 1]]
  &gt;&gt;&gt; 
  </code></pre>
  
  <p>I am using a numpy array as a workarround which I need later on anyway. But I really had hoped that if I used deepcopy I would not have to chase any unintended references any more. Are there any more traps where it does not work?</p>