title: Duplicate elements in a list
body: <p>I have a <code>list</code> in Python:</p>
  
  <pre><code>l = ['a', 'c', 'e', 'b']
  </code></pre>
  
  <p>I want to duplicate each element immediately next to the original.</p>
  
  <pre><code>ll = ['a', 'a', 'c', 'c', 'e', 'e', 'b', 'b']
  </code></pre>
  
  <p>The order of the elements should be preserved.</p>