title: Regular Expression cleaning except abbreviations
body: <p>I'm using <code>[^A-Za-z']</code> expression to clean data from a CSV file before processing it. But I want to keep dots for abbreviations (such as U.S)
  I want to exclude <code>[A-Za-z]\.[A-Za-z]</code> from <code>[^A-Za-z']</code>. How can I do that?</p>
  
  <p>Edit:
  To make it clearer. I will provide an example sentence:</p>
  
  <blockquote>
    <p>"The plastic buildout in the U.S. is clustered in the Gulf of Mexico
    region, where much of the U.S. petrochemical industry is already
    located."</p>
  </blockquote>
  
  <p>I convert to lowercase, clean any characters that aren't alphabetical and divide the sentence into words. When I'm cleaning it, I get the result:</p>
  
  <blockquote>
    <p>"the plastic buildout in the u s is clustered in the gulf of mexico
    region where much of the u s petrochemical industry is already
    located"</p>
  </blockquote>
  
  <p>I want to exclude <code>[A-Za-z]\.[A-Za-z]</code> to ignore U.S </p>
  
  <p>The line of code:</p>
  
  <pre><code>corpus_text['Sentence'] = corpus_text['Sentence'].str.replace("[^A-Za-z']", ' ').str.lower()
  </code></pre>