title: Add a new column to a csv file in python
body: <p>I am trying to add a column to a csv file that combines strings from two other columns. Whenever I try this I either get an output csv with only the new column or an output with all of the original data and not the new column. </p>
  
  <p>This is what I have so far:</p>
  
  <pre><code>with open(filename) as csvin:
      readfile = csv.reader(csvin, delimiter=',')
      with open(output, 'w') as csvout:
          writefile = csv.writer(csvout, delimiter=',', lineterminator='\n')
          for row in readfile:
              result = [str(row[10]) + ' ' + str(row[11])]
              writefile.writerow(result)
  </code></pre>
  
  <p>Any help would be appreciated.</p>