title: python version 3.4 does not support a 'ur' prefix
body: <p>I have some python code writen in an older version of python(2.x) and I struggle to make it work. I'm using python 3.4 </p>
  
  <pre><code>_eng_word = ur"[a-zA-Z][a-zA-Z0-9'.]*"
  </code></pre>
  
  <p>(it's part of a tokenizer)</p>