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Re: python file API

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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

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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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