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Groups > comp.lang.python > #9488

Re: Possible File iteration bug

From Terry Reedy <tjreedy@udel.edu>
Subject Re: Possible File iteration bug
Date 2011-07-14 16:43 -0400
References <ivnh2f$rdc$1@speranza.aioe.org>
Newsgroups comp.lang.python
Message-ID <mailman.1037.1310676208.1164.python-list@python.org> (permalink)

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On 7/14/2011 3:46 PM, Billy Mays wrote:
> I noticed that if a file is being continuously written to, the file
> generator does not notice it:

Because it does not look, as Ian explained.

> def getLines(f):
> lines = []
> for line in f:
> lines.append(line)
> return lines

This nearly duplicates .readlines, except for using f an an iterator.
Try the following (untested):

with open('/var/log/syslog', 'rb') as f:
   lines = f.readlines()
   # do some processing with lines
   # /var/log/syslog gets updated in the mean time
   lines = f.readlines()

People regularly do things like this with readline, so it is possible. 
If above does not work, try (untested):

def getlines(f):
   lines = []
   while True:
     l = f.readline()
     if l: lines.append(l)
     else: return lines

-- 
Terry Jan Reedy

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Thread

Possible File iteration bug Billy Mays <noway@nohow.com> - 2011-07-14 15:46 -0400
  Re: Possible File iteration bug Ian Kelly <ian.g.kelly@gmail.com> - 2011-07-14 14:00 -0600
    Re: Possible File iteration bug Billy Mays <noway@nohow.com> - 2011-07-14 16:15 -0400
      Re: Possible File iteration bug Hrvoje Niksic <hniksic@xemacs.org> - 2011-07-14 22:39 +0200
  Re: Possible File iteration bug Terry Reedy <tjreedy@udel.edu> - 2011-07-14 16:43 -0400
  Re: Possible File iteration bug "bruno.desthuilliers@gmail.com" <bruno.desthuilliers@gmail.com> - 2011-07-15 01:01 -0700
    Re: Possible File iteration bug Billy Mays <noway@nohow.com> - 2011-07-15 08:26 -0400
      Re: Possible File iteration bug Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-07-15 16:21 +0200
      Re: Possible File iteration bug Terry Reedy <tjreedy@udel.edu> - 2011-07-15 17:45 -0400
      Re: Possible File iteration bug Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-07-16 13:42 +1000
        Re: Possible File iteration bug Chris Angelico <rosuav@gmail.com> - 2011-07-16 14:07 +1000
        Re: Possible File iteration bug Cameron Simpson <cs@zip.com.au> - 2011-07-17 09:28 +1000
        Re: Possible File iteration bug Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-07-17 09:26 +0200
  Re: Possible File iteration bug Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-07-15 14:39 +0200
    Re: Possible File iteration bug Billy Mays <noway@nohow.com> - 2011-07-15 08:52 -0400
      Re: Possible File iteration bug Chris Angelico <rosuav@gmail.com> - 2011-07-15 22:58 +1000
      Re: Possible File iteration bug Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-07-15 16:28 +0200
        Re: Possible File iteration bug Billy Mays <81282ed9a88799d21e77957df2d84bd6514d9af6@myhashismyemail.com> - 2011-07-15 10:42 -0400
          Re: Possible File iteration bug Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-07-15 22:46 +0200
          Re: Possible File iteration bug Ethan Furman <ethan@stoneleaf.us> - 2011-07-15 14:20 -0700
          Re: Possible File iteration bug Terry Reedy <tjreedy@udel.edu> - 2011-07-15 17:47 -0400

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