Add support for `VISCII` encoding in `codecs`

[henryivesjones]

Feature or enhancement

Proposal:

viscii is an encoding for the Vietnamese language. Support for it is included in the email charset list but it is not supported by codecs. The encoding spec can be found in rfc1456.

viscii can be found in the IANA character sets list.
https://www.iana.org/assignments/character-sets/character-sets.xhtml

import codecs
codecs.lookup('viscii')
# LookupError: unknown encoding: viscii

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-148865: Add support for viscii encoding in codecs #148866

[serhiy-storchaka]

According to Wikipedia, VISCII is an unofficial encoding which was mostly used by overseas Vietnamese speakers, while VSCII (TCVN) (official standard) and VNI were more popular in Vietnam. Each of them has several variants, so this is a complex issue.

Having an RFC is an argument in favor, but RFC 1456 does not contain a table for Unicode mapping, so it cannot be used to generate the codec. https://vietstd.sourceforge.net/document/unicode.html refers to VISCII 1.1, so the variant described in RFC 1456 is perhaps not final.

iconv supports VISCII and TCVN.

We need a Vietnamese expert to evaluate this.

[encukou]

@henryivesjones, is there a need for this in practice today?

For converting old documents, it seems that you'd commonly need other variants as well. Sounds like a job for specialized tooling rather than stdlib.

@serhiy-storchaka, the RFC describes VISCII 1.1.