Re: python file API

References	<0ec1fe2e-890c-4e25-8047-4cb8bee0aa95@googlegroups.com> <5060D55C.3000407@davea.name>
Date	2012-09-25 08:14 +1000
Subject	Re: python file API
From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.1222.1348524844.27098.python-list@python.org> (permalink)

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On Tue, Sep 25, 2012 at 7:49 AM, Dave Angel <d@davea.name> wrote:
> On 09/24/2012 05:35 PM, zipher wrote:
>> Let file-type have an attribute .pos for position.   Now you can get rid of the seek() and tell() methods and manipulate the file pointer more easily with standard arithmetic operations.
>>
>>>>> file.pos = x0ae1      #move file pointer to an absolute address
>>>>> file.pos +=1            #increment the file pointer one byte
>>>>> curr_pos = file.pos  #read current file pointer
>
> And what approach would you use for positioning relative to
> end-of-file?  That's currently done with an optional second parameter to
> seek() method.

Presumably the same way you reference a list element relative to
end-of-list: negative numbers. However, this starts to feel like magic
rather than attribute assignment - it's like manipulating the DOM in
JavaScript, you set an attribute and stuff happens. Sure it's legal,
but is it right? Also, it makes bounds checking awkward:

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?
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.

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. But
doing the exact same operation on a saved snapshot of the position and
reassigning it would then have quite different semantics in an unusual
case, while still appearing identical in the normal case.

ChrisA

Thread

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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