title: How would you put back a list that you've split and transformed back to the original file?
body: <p>I am trying to isolate date from date/time which is a column in the original csv file. I've isolated the column and change it to just date but I am having a tough time putting it back to the original file:</p>
  
  <pre><code>def isolateDate(csv_file):
      file_in = open(csv_file, "rU")
      reader = csv.reader(file_in)
      next(file_in,None)
      for line in reader:
          date = line[3]
          date = date.split()
          new_date = date[0]
      return new_date
  </code></pre>
  
  <p>How would I go about putting back <code>new_date</code> variable as the <code>line[3]</code> in the original file</p>