getting the line just before or after a pattern searched

[Magnus Lycka]

s99999999s2003 at yahoo.com wrote:
> hi
> 
> i have a file something like this
> 
> abcdefgh
> ijklmnopq
> 12345678
> rstuvwxyz
> .....
> .....
> .....
> 12345678
> .....
> 
> whenever i search the file and reach 12345678, how do i get the line
> just above and below ( or more than 1 line above/below) the pattern
> 12345678 and save to variables? thanks

For gigantic files (i.e. can't put all in RAM at once)
just make sure you always remember the previously read line.
Something like this:

old = None
f = open('mybigfile.txt')
for line in f:
     if line == '12345678\n':
         print old,
         print line,
         print f.next(),
     old=line