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Re: iterating over a file with two pointers

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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.

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Thread

iterating over a file with two pointers nikhil Pandey <nikhilpandey90@gmail.com> - 2013-09-18 04:12 -0700
  Re: iterating over a file with two pointers Chris Angelico <rosuav@gmail.com> - 2013-09-18 21:21 +1000
    Re: iterating over a file with two pointers nikhil Pandey <nikhilpandey90@gmail.com> - 2013-09-18 05:07 -0700
      Re: iterating over a file with two pointers Travis Griggs <travisgriggs@gmail.com> - 2013-09-18 09:18 -0700
  Re: iterating over a file with two pointers Dave Angel <davea@davea.name> - 2013-09-18 11:39 +0000
    Re: iterating over a file with two pointers Roy Smith <roy@panix.com> - 2013-09-18 08:56 -0400
      Re: iterating over a file with two pointers Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-09-18 14:09 +0100
      Re: iterating over a file with two pointers Roy Smith <roy@panix.com> - 2013-09-18 10:36 -0400
      Re: iterating over a file with two pointers Dave Angel <davea@davea.name> - 2013-09-18 20:07 +0000
      Re: iterating over a file with two pointers Peter Otten <__peter__@web.de> - 2013-09-19 09:23 +0200
      Re: iterating over a file with two pointers Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-09-19 15:16 +0100
      Re: iterating over a file with two pointers Peter Otten <__peter__@web.de> - 2013-09-19 16:38 +0200
      Re: iterating over a file with two pointers Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-09-19 15:48 +0100
  Re: iterating over a file with two pointers Peter Otten <__peter__@web.de> - 2013-09-18 13:44 +0200
    Re: iterating over a file with two pointers nikhil Pandey <nikhilpandey90@gmail.com> - 2013-09-18 05:14 -0700
      Re: iterating over a file with two pointers Peter Otten <__peter__@web.de> - 2013-09-18 14:54 +0200
      Re: iterating over a file with two pointers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-19 02:40 +0000
  Re: iterating over a file with two pointers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-19 02:56 +0000
    Re: iterating over a file with two pointers Joshua Landau <joshua@landau.ws> - 2013-09-19 08:04 +0100

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