title: Working with texts: change all letters to lowercase in a CSV file
body: <p>I'm working with a .txt dataset which I read in as a csv file.</p>
  
  <pre><code>data = pd.read_csv('train.txt', delimiter='\t', header=None, names=['category', 'text'], dtype=str)
  print data.head()
  </code></pre>
  
  <p>it prints:</p>
  
  <pre><code>0  MUSIC  Today at the recording studio, John...
  1  POLITICS  The tensions inside the government have...
  2  NEWS  The new pictures of NASA show...
  </code></pre>
  
  <p>What I want to do, is change all the letters from the text to lowercase. So, for example, "The new pictures of NASA show..." would become "the new pictures of nasa show...", but "NEWS" remains uppercase as "NEWS".</p>
  
  <p>Any words of advice?</p>