Column subtractor - Python

I am still struggling with the after effects of Linux reinstallation on my system.
Two major problems:
1) Firefox and openoffice is still not in English. Its giving me hard time.
2) The functions in openoffice  version of excel is not working.

I am yet to sort that out. In the mean time, I desperately needed it to do simple task. subtracting values of one column from one in another column and write the difference in next column.

So, I had input in this form:

------------------


0    2.179139    0.951816
1    2.314531    1.006480
2    2.191692    0.951938
3    2.079704    0.952747
4    2.092761    0.939545
5    2.362056    0.984791
6    2.153595    0.957934
7    2.213173    0.951768
8    2.175687    0.953091

--------------------

I needed to subtract  column 3 data from column 2 data. So, I tried this:

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#!/usr/bin/env python

fo=open('name.txt' +'_output','w')
with open('name.txt') as fd:
 for line in fd:
   columns=line.split()
   columns=map(float,columns)
   fo.write ("%s \t %s \n" %(line.strip(), columns[1] - columns[2]))

-----------------------------

It creates an output with difference written in next column :


---------------------------------
0    2.179139    0.951816      1.227323
1    2.314531    1.006480      1.308051
2    2.191692    0.951938      1.239754
3    2.079704    0.952747      1.126957
4    2.092761    0.939545      1.153216
5    2.362056    0.984791      1.377265
6    2.153595    0.957934      1.195661
7    2.213173    0.951768      1.261405
8    2.175687    0.953091      1.222596

---------------------------------

It works fine, only problem is it ends with an error:

IndexError: list index out of range

Although it doesn't effect the result.
So, for the moment I got the result I wanted but I will come back and take care of this small issue.