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newbie: Some file object tips?

bougle gluce bougle at gluce.com
Tue Feb 19 14:20:23 EST 2002 
"Flavian Hardcastle" <deathtospam43423 at altavista.com> wrote in message
news:Xns91BAF4112B7BEAusYourStandingInIt at 130.133.1.4...
> Gerhard =?unknown-8bit?Q?H=E4ring?= <gh_pythonlist at gmx.de> wrote in
> news:mailman.1014120512.7783.python-list at python.org:
>
> > Le 19/02/02 ? 11:00, Flavian Hardcastle écrivit:
> >>
> >> I'm writing a crude cgi chat script. I've already got it up and
> >> working with Xitami server, and have chatted with a few net buddies.
> >>
> >> How it works is very rough and simple... it basically just takes data
> >> from people's browsers (using the FieldStorage function) and stores it
> >> in a file called log.txt, and then displays the contents of that file
> >> back to them.
> >>
> >> My problem is ...
> >>
> >> The longer you chat, the bigger the log.txt file gets, and
> >> consequently the web page the chatters are viewing gets bigger and
> >> bigger, and becomes hard to download.
> >>
> >> So I want to include a "scroll back" feature ... which will enable the
> >> user to control how many previous posts (s)he views. It will probably
> >> take the form a simple input box on the form ... if you want to see
> >> the last 8 posts, you put 8 in the box, if you want to see the last 50
> >> posts, you put 50 in the box and so on.
> >>
> >> So, I need the script to be able to search the log.txt file. Any tips
> >> as to how I might go about this?
> >
> > You could read the file into a list with
> >
> > lines = open("log.txt").readlines()
> >
> > but now, all the lines will include a newline character at their end.
> > To strip these, you can do the following instead:
> >
> > lines = map(string.rstrip, open("log.txt").readlines())
> >
> > Now you can use slicing on the list, say to return the last 8 lines,
> > you can do:
> >
> > lines[-8:]
> >
> > HTH,
> >
> > Gerhard
>
> Cool! Thanx very much. Never saw that in any of the tutorials!
>
> BTW, one thing I'm concerned about ... I want to avoid the script having
to
> load the entire log.txt file into RAM everytime someone makes a post. You
> see, I estimate that a log file with only 200 posts worth of text would
> weigh about 60k.
>
> If say, ten people, are all posting posting at once that could be as much
> as 600k in the memory. If it's 20 chatters, 1.2 meg. That could take a
> couple of seconds for the servers CPU to process, might noticeably slow
> things down ... especially on my 'puter which is only 500Mhz.
>
> So does this command ....
>
> > lines = open("log.txt").readlines()
>
> ... actually load the whole log into RAM.
>
> --
> cdewin at dingoblue.net.au

yes, readlines() will load the whole fileinto RAM. as an alternative you can
use readline(), which reads one line at a time, or read(n) where n is the
number of bytes you want to read. you can also use seek() to go directly to
a particular place in the file.
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