What's "ANSI_X3.4-1968" encoding?

Question

See following output on my system:

[STEP 101] # python3 -c 'import sys; print(sys.stdout.encoding)'
ANSI_X3.4-1968
[STEP 102] #
[STEP 103] # locale
LANG=C
LANGUAGE=en_US:en
LC_CTYPE="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_COLLATE="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_PAPER="C"
LC_NAME="C"
LC_ADDRESS="C"
LC_TELEPHONE="C"
LC_MEASUREMENT="C"
LC_IDENTIFICATION="C"
LC_ALL=C
[STEP 104] #

Googled but found very little info about it. Even Python's The Python Library Reference (v3.5.2) does not mention it. Any international standard defines it?

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(Copied the authoritative ref from the accepted answer's comment: Character Sets)

Answer 1

This is another name for USAS X3.4-1968, a revision of ASCII that is distinguished by being:

• the first revision to allow a linefeed (LF) to occur on its own (i.e. not preceded by or followed by a carriage return (CR)).

• the revision that introduced the common name of (US-)ASCII.

This is basically ASCII as we think of it, although there were two minor revisions that followed it.

Answer 2

If you're curious where it comes from in cpython, the value is computed from the locale module using langinfo.

Here's a tiny C program which demonstrates how the _locale module determines this information:

#include <langinfo.h>
#include <locale.h>
#include <stdio.h>

int main () {
    setlocale(LC_ALL, "");
    printf("%s\n", nl_langinfo(CODESET));
    return 0;
}

And some sample output:

$ LANG= ./a.out 
ANSI_X3.4-1968
$ LANG=en_US.UTF-8 ./a.out 
UTF-8

python normalizes the ansi name to ascii (or US-ASCII)