readline() - problem

[piotr at kolodziejczyk.waw.pl]

Hi!
I'm a new user of python, and have problem.
I have a plain ascii file:
1aaaaaaaaaaaa1......1
1cccccccccccc2......1
1xxxxxxxxxxxx1......1
I want to create a new file which contains only lines with '1' on 15th
position.
I've tried this:

import string
f=open('/test/test.asc','r')
o=open('/test/out.asc','w')
for line in f:
    s= f.readline()
    if s[15]=='1' :
       o.write(s)
o.close()
f.close()

Why it doesn't work ('s' contains ' ' )?

piotr