How to support a non-standard encoding?

[jmfauth]

On 6 jan, 11:03, Ivan <i... at llaisdy.com> wrote:
> Dear All
>
> I'm developing a python application for which I need to support a
> non-standard character encoding (specifically ISO 6937/2-1983, Addendum
> 1-1989).  Here are some of the properties of the encoding and its use in
> the application:
>
>    - I need to read and write data to/from files.  The file format
>      includes two sections in different character encodings (so I
>      shan't be able to use codecs.open()).
>
>    - iso-6937 sections include non-printing control characters
>
>    - iso-6937 is a variable width encoding, e.g. "A" = [41],
>      "Ä" = [0xC8, 0x41]; all non-spacing diacritical marks are in the
>      range 0xC0-0xCF.
>
> By any chance is there anyone out there working on iso-6937?
>
> Otherwise, I think I need to write a new codec to support reading and
> writing this data.  Does anyone know of any tutorials or blog posts on
> implementing a codec for a non-standard characeter encoding?  Would
> anyone be interested in reading one?
>


Take a look at the files, Python modules, in the
...\Lib\encodings. This is the place where all codecs
are centralized. Python is magically using these
a long there are present in that dir.

I remember, long time ago, for the fun, I created such
a codec quite easily. I picked up one of the file as
template and I modified its "table". It was a
byte <-> byte table.

For multibytes coding scheme, it may be a litte bit more
complicated; you may take a look, eg, at the mbcs.py codec.

The distibution of such a codec may be a problem.

----

Another simple approach, os independent.

You probably do not write your code in iso-6937, but
you only need to encode/decode some bytes sequence
"on the fly". In that case, work with bytes, create
a couple of coding / decoding functions with a
created <dict> [*] as helper. It's not so complicate.
Use <unicode> Py2 or <str> Py3 (the recommended
way ;-) ) as pivot encoding.

[*] I also created once a such a dict from
# http://www.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WindowsBestFit/bestfit1252.txt

I never checked if it does correpond to the "official" cp1252
codec.

jmf