How to add a new column to a CSV file?

Question

I have several CSV files that look like this:

Input Name        Code blackberry  1 wineberry   2 rasberry    1 blueberry   1 mulberry    2 

I would like to add a new column to all CSV files so that it would look like this:

Output Name        Code    Berry blackberry  1   blackberry wineberry   2   wineberry rasberry    1   rasberry blueberry   1   blueberry mulberry    2   mulberry 

The script I have so far is this:

import csv with open(input.csv,'r') as csvinput:     with open(output.csv, 'w') as csvoutput:         writer = csv.writer(csvoutput)         for row in csv.reader(csvinput):             writer.writerow(row+['Berry']) 

(Python 3.2)

But in the output, the script skips every line and the new column has only Berry in it:

Output Name        Code    Berry blackberry  1   Berry  wineberry   2   Berry  rasberry    1   Berry  blueberry   1   Berry  mulberry    2   Berry 

Answer 1

This should give you an idea of what to do:

>>> v = open('C:/test/test.csv') >>> r = csv.reader(v) >>> row0 = r.next() >>> row0.append('berry') >>> print row0 ['Name', 'Code', 'berry'] >>> for item in r: ...     item.append(item[0]) ...     print item ...      ['blackberry', '1', 'blackberry'] ['wineberry', '2', 'wineberry'] ['rasberry', '1', 'rasberry'] ['blueberry', '1', 'blueberry'] ['mulberry', '2', 'mulberry'] >>>  

Edit, note in py3k you must use next(r)

Thanks for accepting the answer. Here you have a bonus (your working script):

import csv  with open('C:/test/test.csv','r') as csvinput:     with open('C:/test/output.csv', 'w') as csvoutput:         writer = csv.writer(csvoutput, lineterminator='\n')         reader = csv.reader(csvinput)          all = []         row = next(reader)         row.append('Berry')         all.append(row)          for row in reader:             row.append(row[0])             all.append(row)          writer.writerows(all) 

Please note

1. the lineterminator parameter in csv.writer. By default it is set to '\r\n' and this is why you have double spacing.
2. the use of a list to append all the lines and to write them in one shot with writerows. If your file is very, very big this probably is not a good idea (RAM) but for normal files I think it is faster because there is less I/O.

3. As indicated in the comments to this post, note that instead of nesting the two with statements, you can do it in the same line:

   with open('C:/test/test.csv','r') as csvinput, open('C:/test/output.csv', 'w') as csvoutput:

Answer 2

I'm surprised no one suggested Pandas. Although using a set of dependencies like Pandas might seem more heavy-handed than is necessary for such an easy task, it produces a very short script and Pandas is a great library for doing all sorts of CSV (and really all data types) data manipulation. Can't argue with 4 lines of code:

import pandas as pd csv_input = pd.read_csv('input.csv') csv_input['Berries'] = csv_input['Name'] csv_input.to_csv('output.csv', index=False) 

Check out Pandas Website for more information!

Contents of output.csv:

Name,Code,Berries blackberry,1,blackberry wineberry,2,wineberry rasberry,1,rasberry blueberry,1,blueberry mulberry,2,mulberry