iterating over a file with two pointers

[nikhil Pandey]

On Wednesday, September 18, 2013 5:14:10 PM UTC+5:30, Peter Otten wrote:
> nikhil Pandey wrote:
> 
> 
> 
> > hi,
> 
> > I want to iterate over the lines of a file and when i find certain lines,
> 
> > i need another loop starting from the next of that "CERTAIN" line till a
> 
> > few (say 20) lines later. so, basically i need two pointers to lines (one
> 
> > for outer loop(for each line in file)) and one for inner loop. How can i
> 
> > do that in python? please help. I am stuck up on this.
> 
> 
> 
> Here's an example that prints the three lines following a line containing a 
> 
> '*':
> 
> 
> 
> Example data:
> 
> 
> 
> $ cat tmp.txt
> 
> alpha
> 
> *beta
> 
> *gamma
> 
> delta
> 
> epsilon
> 
> zeta
> 
> *eta
> 
> 
> 
> The python script:
> 
> 
> 
> $ cat tmp.py
> 
> from itertools import islice, tee
> 
> 
> 
> with open("tmp.txt") as f:
> 
>     while True:
> 
>         for outer in f:
> 
>             print outer,
> 
>             if "*" in outer:
> 
>                 f, g = tee(f)
> 
>                 for inner in islice(g, 3):
> 
>                     print "   ", inner,
> 
>                 break
> 
>         else:
> 
>             break
> 
> 
> 
> The script's output:
> 
> 
> 
> $ python tmp.py
> 
> alpha
> 
> *beta
> 
>     *gamma
> 
>     delta
> 
>     epsilon
> 
> *gamma
> 
>     delta
> 
>     epsilon
> 
>     zeta
> 
> delta
> 
> epsilon
> 
> zeta
> 
> *eta
> 
> $ 
> 
> 
> 
> As you can see the general logic is relatively complex; it is likely that we 
> 
> can come up with a simpler solution if you describe your actual requirement 
> 
> in more detail.

hi,
I want to iterate in the inner loop by reading each line till some condition is met.how can i do that. Thanks for this code.