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

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Date Thu, 29 Mar 2012 16:57:19 +0200
From Peter Daum <gator@cs.tu-berlin.de>
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Subject Re: "convert" string to bytes without changing data (encoding)
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On 2012-03-28 23:37, Terry Reedy wrote:
> 2. Decode as if the text were latin-1 and ignore the non-ascii 'latin-1'
> chars. When done, encode back to 'latin-1' and the non-ascii chars will
> be as they originally were.

... actually, in the beginning of my quest, I ran into an decoding
exception trying to read data as "latin1" (which was more or less what
I had expected anyway because byte values between 128 and 160 are not
defined there).

Obviously, I must have misinterpreted something there;
I just ran a little test:

  l=[i for i in range(256)]; b=bytes(l)
  s=b.decode('latin1'); b=s.encode('latin1'); s=b.decode('latin1')
  for c in s:
      print(hex(ord(c)), end=' ')
      if (ord(c)+1) % 16 ==0: print("")
  print()

... and got all the original bytes back. So it looks like I tried to
solve a problem that did not exist to start with (the problems, I ran
into then were pretty real, though ;-)

> 3. Decode using encoding = 'ascii', errors='surrogate_escape'. This
> reversibly encodes the unknown non-ascii chars as 'illegal' non-chars
> (using the surrogate-pair second-half code units). This is probably the
> safest in that invalid operations on the non-chars should raise an
> exception. Re-encoding with the same setting will reproduce the original
> hi-bit chars. The main danger is passing the illegal strings out of your
> local sandbox.

Unfortunately, this is a very well-kept secret unless you know that
something with that name exists. The options currently mentioned in the
documentation are not really helpful, because the non-decodeable will
be lost. With some trying, I got it to work, too (the option is named
"surrogateescape" without the "_" and in python 3.1 it exists, but only
not as a keyword argument: "s=b.decode('utf-8','surrogateescape')" ...)

Thank you very much for your constructive advice!

Regards,
                                 Peter

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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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