title: PYTHON - How to extract sentences containing citation mark from text file
body: <p>For example, I have 3 sentences like at below where 1 sentence in the middle contains citation mark <code>(Warren and Pereira, 1982)</code>. The citation is always in bracket with this format: (~string~comma(,)~space~number~)</p>
  
  <blockquote>
    <p>He lives in Nidarvoll and tonight i must reach a train to Oslo at 6 oclock. The system, called BusTUC is built upon the classical system CHAT-80 (Warren and Pereira, 1982). CHAT-80 was a state of the art natural language system that was 
    impressive on its own merits.</p>
  </blockquote>
  
  <p>I'm using Regex to extract only the middle sentence but it keeps print all the 3 sentences.
  The result should be like this:</p>
  
  <blockquote>
    <p>The system, called BusTUC is built upon the classical system CHAT-80 (Warren and Pereira, 1982).</p>
  </blockquote>