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

From	Terry Reedy <tjreedy@udel.edu>
Subject	Re: "convert" string to bytes without changing data (encoding)
Date	2012-03-28 14:11 -0400
References	<9tg21lFmo3U1@mid.dfncis.de> <mailman.1065.1332925364.3037.python-list@python.org> <jkvb5a$88d$1@rumours.uwaterloo.ca>
Newsgroups	comp.lang.python
Message-ID	<mailman.1087.1332959217.3037.python-list@python.org> (permalink)

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On 3/28/2012 11:36 AM, Ross Ridge wrote:
> Chris Angelico<rosuav@gmail.com>  wrote:
>> What is a string? It's not a series of bytes.
>
> Of course it is.  Conceptually you're not supposed to think of it that
> way, but a string is stored in memory as a series of bytes.

*If* it is stored in byte memory. If you execute a 3.x program mentally 
or on paper, then there are no bytes.

If you execute a 3.3 program on a byte-oriented computer, then the 'a' 
in the string might be represented by 1, 2, or 4 bytes, depending on the 
other characters in the string. The actual logical bit pattern will 
depend on the big versus little endianness of the system.

My impression is that if you go down to the physical bit level, then 
again there are, possibly, no 'bytes' as a physical construct as the 
bits, possibly, are stored in parallel on multiple ram chips.

> What he's asking for many not be very useful or practical, but if that's
> your problem here than then that's what you should be addressing, not
> pretending that it's fundamentally impossible.

The python-level way to get the bytes of an object that supports the 
buffer interface is memoryview(). 3.x strings intentionally do not 
support the buffer interface as there is not any particular 
correspondence between characters (codepoints) and bytes.

The OP could get the ordinal for each character and decide how *he* 
wants to convert them to bytes.

ba = bytearray()
for c in s:
   i = ord(c)
   <append bytes to ba corresponding to i>

To get the particular bytes used for a particular string on a particular 
system, OP should use the C API, possibly through ctypes.

-- 
Terry Jan Reedy

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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