Re: "convert" string to bytes without changing data (encoding)

References	<9tg21lFmo3U1@mid.dfncis.de> <mailman.1065.1332925364.3037.python-list@python.org> <9tg4qoFbfpU1@mid.dfncis.de> <mailman.1069.1332931371.3037.python-list@python.org> <9th0u8Fuf2U1@mid.dfncis.de>
From	Ian Kelly <ian.g.kelly@gmail.com>
Date	2012-03-28 12:20 -0600
Subject	Re: "convert" string to bytes without changing data (encoding)
Newsgroups	comp.lang.python
Message-ID	<mailman.1086.1332958864.3037.python-list@python.org> (permalink)

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On Wed, Mar 28, 2012 at 11:43 AM, Peter Daum <gator@cs.tu-berlin.de> wrote:
> ... I was under the illusion, that python (like e.g. perl) stored
> strings internally in utf-8. In this case the "conversion" would simple
> mean to re-label the data. Unfortunately, as I meanwhile found out, this
> is not the case (nor the "apple encoding" ;-), so it would indeed be
> pretty useless.

No, unicode strings can be stored internally as any of UCS-1, UCS-2,
UCS-4, C wchar strings, or even plain ASCII.  And those are all
implementation details that could easily change in future versions of
Python.

> The longer story of my question is: I am new to python (obviously), and
> since I am not familiar with either one, I thought it would be advisory
> to go for python 3.x. The biggest problem that I am facing is, that I
> am often dealing with data, that is basically text, but it can contain
> 8-bit bytes. In this case, I can not safely assume any given encoding,
> but I actually also don't need to know - for my purposes, it would be
> perfectly good enough to deal with the ascii portions and keep anything
> else unchanged.

You can't generally just "deal with the ascii portions" without
knowing something about the encoding.  Say you encounter a byte
greater than 127.  Is it a single non-ASCII character, or is it the
leading byte of a multi-byte character?  If the next character is less
than 127, is it an ASCII character, or a continuation of the previous
character?  For UTF-8 you could safely assume ASCII, but without
knowing the encoding, there is no way to be sure.  If you just assume
it's ASCII and manipulate it as such, you could be messing up
non-ASCII characters.

Cheers,
Ian

Thread

"convert" string to bytes without changing data (encoding) Peter Daum <gator@cs.tu-berlin.de> - 2012-03-28 10:56 +0200
  Re: "convert" string to bytes without changing data (encoding) Chris Angelico <rosuav@gmail.com> - 2012-03-28 20:02 +1100
    Re: "convert" string to bytes without changing data (encoding) Peter Daum <gator@cs.tu-berlin.de> - 2012-03-28 11:43 +0200
      Re: "convert" string to bytes without changing data (encoding) Heiko Wundram <modelnine@modelnine.org> - 2012-03-28 12:42 +0200
        Re: "convert" string to bytes without changing data (encoding) Peter Daum <gator@cs.tu-berlin.de> - 2012-03-28 19:43 +0200
          Re: "convert" string to bytes without changing data (encoding) Heiko Wundram <modelnine@modelnine.org> - 2012-03-28 20:13 +0200
          Re: "convert" string to bytes without changing data (encoding) Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2012-03-28 21:13 +0300
            RE: "convert" string to bytes without changing data (encoding) "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-03-28 18:31 +0000
            Re: "convert" string to bytes without changing data (encoding) Ethan Furman <ethan@stoneleaf.us> - 2012-03-28 11:49 -0700
          RE: "convert" string to bytes without changing data (encoding) "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-03-28 18:20 +0000
          Re: "convert" string to bytes without changing data (encoding) Ian Kelly <ian.g.kelly@gmail.com> - 2012-03-28 12:20 -0600
          Re: "convert" string to bytes without changing data (encoding) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-03-28 18:26 +0000
            Re: "convert" string to bytes without changing data (encoding) Grant Edwards <invalid@invalid.invalid> - 2012-03-28 19:40 +0000
          Re: "convert" string to bytes without changing data (encoding) Ethan Furman <ethan@stoneleaf.us> - 2012-03-28 11:17 -0700
          Re: "convert" string to bytes without changing data (encoding) John Nagle <nagle@animats.com> - 2012-03-28 12:30 -0700
          Re: "convert" string to bytes without changing data (encoding) Terry Reedy <tjreedy@udel.edu> - 2012-03-28 17:37 -0400
            Re: "convert" string to bytes without changing data (encoding) Peter Daum <gator@cs.tu-berlin.de> - 2012-03-29 16:57 +0200
            Re: "convert" string to bytes without changing data (encoding) Peter Daum <gator@cs.tu-berlin.de> - 2012-03-29 16:57 +0200
          Re: "convert" string to bytes without changing data (encoding) Serhiy Storchaka <storchaka@gmail.com> - 2012-03-30 22:06 +0300
          Re: "convert" string to bytes without changing data (encoding) Chris Angelico <rosuav@gmail.com> - 2012-03-31 06:10 +1100
      Re: "convert" string to bytes without changing data (encoding) Stefan Behnel <stefan_ml@behnel.de> - 2012-03-28 13:25 +0200
      Re: "convert" string to bytes without changing data (encoding) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-03-28 18:12 +0000
    Re: "convert" string to bytes without changing data (encoding) Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-03-28 11:36 -0400
      Re: "convert" string to bytes without changing data (encoding) Chris Angelico <rosuav@gmail.com> - 2012-03-29 03:18 +1100
        Re: "convert" string to bytes without changing data (encoding) Grant Edwards <invalid@invalid.invalid> - 2012-03-28 16:33 +0000
        Re: "convert" string to bytes without changing data (encoding) Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-03-28 14:05 -0400
          Re: "convert" string to bytes without changing data (encoding) Tim Chase <python.list@tim.thechases.com> - 2012-03-28 13:49 -0500
            Re: "convert" string to bytes without changing data (encoding) Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-03-28 15:10 -0400
          Re: "convert" string to bytes without changing data (encoding) "Albert W. Hopkins" <marduk@letterboxes.org> - 2012-03-28 15:22 -0400
      Re: "convert" string to bytes without changing data (encoding) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-03-28 17:54 +0000
        Re: "convert" string to bytes without changing data (encoding) Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-03-28 14:22 -0400
          Re: Re: "convert" string to bytes without changing data (encoding) Evan Driscoll <driscoll@cs.wisc.edu> - 2012-03-28 14:20 -0500
            Re: Re: "convert" string to bytes without changing data (encoding) Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-03-28 15:43 -0400
              Re: "convert" string to bytes without changing data (encoding) Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-03-28 21:44 +0100
              Re: "convert" string to bytes without changing data (encoding) Neil Cerutti <neilc@norwich.edu> - 2012-03-28 20:56 +0000
              Re: "convert" string to bytes without changing data (encoding) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-03-29 00:02 +0000
              Re: Re: Re: "convert" string to bytes without changing data (encoding) Evan Driscoll <driscoll@cs.wisc.edu> - 2012-03-28 19:11 -0500
                Re: Re: Re: "convert" string to bytes without changing data (encoding) Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-03-28 23:04 -0400
                Re: Re: Re: "convert" string to bytes without changing data (encoding) Chris Angelico <rosuav@gmail.com> - 2012-03-29 14:31 +1100
                Re: Re: Re: "convert" string to bytes without changing data (encoding) Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-03-28 23:58 -0400
                Re: "convert" string to bytes without changing data (encoding) Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-03-29 07:01 +0100
                Re: "convert" string to bytes without changing data (encoding) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-03-29 06:51 +0000
                Re: "convert" string to bytes without changing data (encoding) Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-03-29 11:30 -0400
                Re: "convert" string to bytes without changing data (encoding) Terry Reedy <tjreedy@udel.edu> - 2012-03-29 12:49 -0400
                Re: "convert" string to bytes without changing data (encoding) Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-03-29 14:00 -0400
                Re: "convert" string to bytes without changing data (encoding) Chris Angelico <rosuav@gmail.com> - 2012-03-30 07:41 +1100
                Re: "convert" string to bytes without changing data (encoding) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-03-30 01:16 +0000
                Re: Re: Re: Re: "convert" string to bytes without changing data (encoding) Evan Driscoll <driscoll@cs.wisc.edu> - 2012-03-29 11:31 -0500
          RE: "convert" string to bytes without changing data (encoding) "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-03-28 19:02 +0000
            Re: "convert" string to bytes without changing data (encoding) Grant Edwards <invalid@invalid.invalid> - 2012-03-28 19:44 +0000
          Re: "convert" string to bytes without changing data (encoding) MRAB <python@mrabarnett.plus.com> - 2012-03-28 20:50 +0100
          RE: "convert" string to bytes without changing data (encoding) "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-03-29 17:36 +0000
            Re: "convert" string to bytes without changing data (encoding) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-03-30 01:10 +0000
              Re: "convert" string to bytes without changing data (encoding) Michael Ströder <michael@stroeder.com> - 2012-03-30 09:04 +0200
      Re: "convert" string to bytes without changing data (encoding) Terry Reedy <tjreedy@udel.edu> - 2012-03-28 14:11 -0400
  Re: "convert" string to bytes without changing data (encoding) Stefan Behnel <stefan_ml@behnel.de> - 2012-03-28 11:08 +0200
  Re: "convert" string to bytes without changing data (encoding) Dave Angel <d@davea.name> - 2012-03-28 13:16 -0400

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