[BangPypers] [Novice] Question on File seek and tell methods

[davidsnt]

Thank you all for your help, I managed to get what I wanted from the file
with all your help, but still I  have my question left opened, cant we get
this done with seek and tell methods, agree that we have a better way, but
want to know the possibilities of getting done with seek and tell.

Read the file, check for matching pattern, get the cursor position with
tell, seek the cursor to the same position and start reading from there
until the next matching position, can you help me with seek and tell
methods to achieve the above case.


Thanks,
David


On Mon, Jun 17, 2013 at 4:46 PM, saurabh <saurabh.hirani at gmail.com> wrote:

> Jonathan has given quite a good answer which I think would solve your
> problem. Here's my take on it. The way of looking at it is a little
> different but Jonathan's approach is much simpler.
>
> The problem is that when you do "for line in f" you are using Python's
> iterators and they are not rewindable i.e. "for line in f" gives call the
> next() function but there is no way to go back when you use iterators. You
> can solve your problem with the following snippet of code.
>
> #!/usr/bin/env python
>
> import re
> import sys
>
> # not doing input validation
> # call program as: python prog.py start_keyword stop_keyword file_to_read
> startat = sys.argv[1]
> stopat = sys.argv[2]
> inputfile = sys.argv[3]
>
> re_startat = re.compile(r'^%s$' % (startat))
> re_stopat = re.compile(r'^%s$' % (stopat))
> pattern = re_startat
>
> with open(inputfile) as f:
>     line = f.readline()
>     inrange = False
>     while line:
>         match = re.search(pattern, line)
>         # if the pattern matches
>         if (match):
>             # and we are not in range of startat - stopat
>             if (not inrange):
>                 # get in range and change the pattern
>                 inrange = True
>                 pattern = re_stopat
>             else:
>                 # we are in the range => stopat pattern matched
>                 # print line and exit
>                 print line
>                 break
>         if (inrange):
>             # we are in range + stopat pattern not matched
>             # keep on printing
>             print line
>         line = f.readline()
>
> It does look prettier in vim on a black screen though :)
>
> The idea is you are "in range" if you have matched your first keyword and
> till you stay in the range you keep on printing. When you find your next
> keyword, you are "out of the range"  and you exit.
>
> Hope that helps.
>
> --
> regards,
> Saurabh.
> http://curiosityhealsthecat.blogspot.in/
>
>
>
> --
> View this message in context:
> http://python.6.x6.nabble.com/Novice-Question-on-File-seek-and-tell-methods-tp5021174p5021552.html
> Sent from the Bangalore (BangPypers) mailing list archive at Nabble.com.
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