`KhiopsDictionaryDomain` JSON export method doesn't work.

[folmos-at-orange]

Description

KhiopsDictionaryDomain.write_khiops_json_file doesn't work. Neither to_dict.

Questions/Ideas

To reproduce

# _bug.py
import json
import sys
from khiops import core as kh


kdom = kh.read_dictionary_file(f"{kh.get_samples_dir()}/Iris/Iris.kdic")
json.dump(kdom.to_dict(), sys.stdout)
kdom.write_khiops_json_file("iris_kdic.json")

Output

❯ python _bug.py | jq
{
  "tool": "Khiops Dictionary",
  "version": "11.0.0",
  "khiops_encoding": "ascii"
}

❯ jq . iris_kdic.json
{
  "tool": "Khiops Dictionary",
  "version": "11.0.0",
  "khiops_encoding": "ascii"
}

[popescu-v]

We need to proceed as for the reports and implement custom to_dict method for each of the classes DictionaryDomain, Dictionary, DictionaryDomain, Dictionary, Variable, VariableBlock, MetaData, Rule.

Then, we need to add test that DictionaryDomain.to_dict serializes the object correctly.

[popescu-v]

However, the regression has minimal consequences for the end-user of the library, because serializing Khiops dictionaries to JSON would only be useful in a niche context, like persisting a dictionary domain for further consumption for update via the Python library itself. The mainstream usage is to edit the dictionary domain in the Python library for consumption by Khiops core, which can only read dictionaries in the KDIC format.

Hence, this issue will be tackled by overriding to_dict on all Khiops dictionary objects (as listed in the previous comment) so that it raises NotImplementedError.