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Groups > comp.lang.python > #9573

Re: Possible File iteration bug

From Terry Reedy <tjreedy@udel.edu>
Subject Re: Possible File iteration bug
Date 2011-07-15 17:45 -0400
References <ivnh2f$rdc$1@speranza.aioe.org> <9f5ddd41-79a7-46a6-b5fe-dd94600d581a@j15g2000yqf.googlegroups.com> <ivpblc$qk4$1@speranza.aioe.org>
Newsgroups comp.lang.python
Message-ID <mailman.1080.1310766347.1164.python-list@python.org> (permalink)

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On 7/15/2011 8:26 AM, Billy Mays wrote:
> On 07/15/2011 04:01 AM, bruno.desthuilliers@gmail.com wrote:
>> On Jul 14, 9:46 pm, Billy Mays<no...@nohow.com> wrote:
>>> I noticed that if a file is being continuously written to, the file
>>> generator does not notice it:
>>>
>>> def getLines(f):
>>> lines = []
>>> for line in f:
>>> lines.append(line)
>>> return lines
>>
>> what's wrong with file.readlines() ?
>
> Using that will read the entire file into memory which may not be

So will getLines.

> possible. In the library reference, it mentions that using the generator
> (which calls file.next()) uses a read ahead buffer to efficiently loop
> over the file. If I call .readline() myself, I forfeit that performance
> gain.

Are you sure? Have you measured the difference?

-- 
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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