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Re: python file API

References <0ec1fe2e-890c-4e25-8047-4cb8bee0aa95@googlegroups.com> <5060D55C.3000407@davea.name> <CAPTjJmpHaprEcemVP+7mwNf2XL=_x60Ye7V3-fQ_Fik=1do5Mw@mail.gmail.com>
From Ian Kelly <ian.g.kelly@gmail.com>
Date 2012-09-24 16:37 -0600
Subject Re: python file API
Newsgroups comp.lang.python
Message-ID <mailman.1229.1348526265.27098.python-list@python.org> (permalink)

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On Mon, Sep 24, 2012 at 4:14 PM, Chris Angelico <rosuav@gmail.com> wrote:
> file.pos = 42 # Okay, you're at position 42
> file.pos -= 10 # That should put you at position 32
> foo = file.pos # Presumably foo is the integer 32
> file.pos -= 100 # What should this do?

Since ints are immutable, the language specifies that it should be the
equivalent of "file.pos = file.pos - 100", so it should set the file
pointer to 68 bytes before EOF.

> foo -= 100 # But this sets foo to the integer -68
> file.pos = foo # And this would set the file pointer 68 bytes from end-of-file.

Which is the same result.

> I don't see it making sense for "file.pos -= 100" to suddenly put you
> near the end of the file; it should either cap and put you at position
> 0, or do what file.seek(-100,1) would do and throw an exception.

I agree, but the language doesn't allow those semantics.

Also, what about the use of `f.seek(0, os.SEEK_END)` to seek to EOF?
I'm not certain what the use cases are, but a quick google reveals
that this does happen in real code.  If a pos of 0 means BOF, and a
pos of -1 means 1 byte before EOF, then how do you seek to EOF without
knowing the file length?

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python file API zipher <dreamingforward@gmail.com> - 2012-09-24 14:35 -0700
  Re: python file API Dave Angel <d@davea.name> - 2012-09-24 17:49 -0400
    Re: python file API Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2012-09-25 08:22 +0200
      Re: python file API Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-09-25 04:19 -0400
        Re: python file API Grant Edwards <invalid@invalid.invalid> - 2012-09-25 14:07 +0000
      Re: python file API Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-09-25 12:07 -0400
      Re: python file API Chris Angelico <rosuav@gmail.com> - 2012-09-26 02:12 +1000
  Re: python file API Chris Kaynor <ckaynor@zindagigames.com> - 2012-09-24 14:58 -0700
  Re: python file API Chris Angelico <rosuav@gmail.com> - 2012-09-25 08:14 +1000
    Re: python file API zipher <dreamingforward@gmail.com> - 2012-09-24 15:36 -0700
      Re: python file API Mark Adam <dreamingforward@gmail.com> - 2012-09-24 21:32 -0500
      Re: python file API Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-09-25 08:27 +0100
      Re: python file API Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-09-25 11:51 +0100
    Re: python file API zipher <dreamingforward@gmail.com> - 2012-09-24 15:36 -0700
      Re: python file API Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-25 02:28 +0000
        Re: python file API Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-09-25 07:25 +0200
          Re: python file API Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-25 07:28 +0000
            Re: python file API Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-09-25 21:40 +0200
    Re: python file API Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-25 01:33 +0000
  Re: python file API Dave Angel <d@davea.name> - 2012-09-24 18:36 -0400
  Re: python file API Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-24 16:37 -0600
    Re: python file API Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-09-25 07:32 +0200
      Re: python file API Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-09-25 04:13 -0400
        Re: python file API Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-09-25 11:53 +0200
      Re: python file API Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-25 03:32 -0600
  Re: python file API Chris Angelico <rosuav@gmail.com> - 2012-09-25 08:57 +1000
  Re: python file API Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-09-25 00:12 +0100
  Re: python file API Chris Kaynor <ckaynor@zindagigames.com> - 2012-09-24 16:14 -0700
  Re: python file API Ramchandra Apte <maniandram01@gmail.com> - 2012-09-30 05:50 -0700

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