title: Why am I unable to assign to a particular element in a list of lists
body: <p>I don't understand why I am assigning to the first element in every list below:</p>
  
  <pre><code>➜  ~  python
  Python 2.7.3 (default, Sep 26 2012, 21:53:58) 
  [GCC 4.7.2] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; board = [[None]*5]*5
  &gt;&gt;&gt; print board
  [[None, None, None, None, None], [None, None, None, None, None], [None, None, None, None, None], [None, None, None, None, None], [None, None, None, None, None]]
  &gt;&gt;&gt; board[0][0] = 1
  &gt;&gt;&gt; print board
  [[1, None, None, None, None], [1, None, None, None, None], [1, None, None, None, None], [1, None, None, None, None], [1, None, None, None, None]]
  </code></pre>
  
  <p>I would expect the final output to be this:</p>
  
  <pre><code>[[1, None, None, None, None], [None, None, None, None, None], [None, None, None, None, None], [None, None, None, None, None], [None, None, None, None, None]]
  </code></pre>