title: Appending item to lists within a list comprehension
body: <p>I have a list, let's say, <code>a = [[1,2],[3,4],[5,6]]</code></p>
  
  <p>I want to add the string <code>'a'</code> to each item in the list <code>a</code>.</p>
  
  <p>When I use:</p>
  
  <pre><code>a = [x.append('a') for x in a] 
  </code></pre>
  
  <p>it returns <code>[None,None,None]</code>. </p>
  
  <p>But if I use:</p>
  
  <pre><code>a1 = [x.append('a') for x in a]
  </code></pre>
  
  <p>then it does something odd. </p>
  
  <p><code>a</code>, but not <code>a1</code> is <code>[[1,2,'a'],[3,4,'a'],[5,6,'a']]</code>. </p>
  
  <p>I don't understand why the first call returns <code>[None, None, None]</code> nor why the second changes on <code>a</code> instead of <code>a1</code>. </p>