title: how to fill a dict with None for all keys (given in a list) in Python 3.3
body: <p>For a <code>writerow</code> of a <code>csv.DictWriter</code>, I need to fill a (part of a) dictionary to be empty. I found no immediate solution for it. Is there one?</p>
  
  <p>Like with</p>
  
  <pre><code>fieldnames = ['first','last']
  </code></pre>
  
  <p>Pseudocode</p>
  
  <pre><code>row = fieldnames.fill(None)
  </code></pre>
  
  <p>Result</p>
  
  <pre><code>print(row)
  ['first':None,'last':None]
  </code></pre>
  
  <p>So that</p>
  
  <pre><code>destination.writerow(row)
  </code></pre>
  
  <p>results in</p>
  
  <pre><code>,
  </code></pre>