[Tutor] swapping lines between files

[Kent Johnson]

On Mon, Mar 23, 2009 at 12:39 PM, Bala subramanian
<bala.biophysics at gmail.com> wrote:
> Dear Friends,
>
> Thanks for your replies for my previous mail.
>
> I have two files as follows.
>
> file 1         file2
> 200           1         3.55
> 210           2         4.55
> 242           3         1.22
> 248           4         3.10
> 256            5        1.11
>
> Now i have to replace 1,2,3,4,5 in file 2 with 200,210,242,248,256 in file1.
> Simply replacing position 1 in file2 with values in file1. Can i do it with
> zip function, if yes how to do it. Here both files contain same number of
> lines.

You can use zip() to combine the lines of the files. itertools.izip()
might be a better choice because it doesn't read the entire file at
once. Something like this (untested):

from itertools import izip
file2 = open(...)
out = open(..., 'w') # output file
for line1, line2 in izip(file1, file2):
  # now create a line that merges the two and write it
  line1 = line1.strip()  # remove newline
  line2items = line2.split()
  line2items[0] = line1
  newLine = '\t'.join(line2items)
  out.write(newLine)
  out.write('\n')
out.close()

Kent