Update JSON schema version and library

[markkuriekkinen]

Update the JSON schema version (json-schema.org) used by python-grader-utils so that it would not print warnings. Currently, all graders print warnings about the schema draft version. They are visible in the A+ inspect submission page.

[raphendyr]

Might be a good idea to replace the json schema object library. Roman contains possible alternative (apluslms_yamlidator).

[markkuriekkinen]

It would be good to also upgrade the PyYAML library to the latest stable release. Currently, setup.py lists version 3.13 as the dependency. The v5 series has small changes to the API.

[markkuriekkinen]

Like was said in #25, upgrading jsonschema and python_jsonschema_objects does not remove the warning. I thought it would. This page says that the draft-07 is supported by the library python-jsonschema: https://python-jsonschema.readthedocs.io/en/latest/validate/#jsonschema.Draft7Validator
Well, the warning actually comes from python_jsonschema_objects and its documentation only mentions draft-04: https://github.com/cwacek/python-jsonschema-objects/blob/master/python_jsonschema_objects/examples/README.md#draft-keyword-support

Therefore, it looks like we should switch python_jsonschema_objects to something else like raphendyr suggested earlier.

[raphendyr]

FYI: apluslms_yamlidator uses ruamel.yaml as the yaml parser, which supports YAML 1.2. See https://yaml.readthedocs.io/en/latest/pyyaml.html .

This might be relevant for some use cases. Although. the yaml documents are small, so I don't think this would actually matter a lot specially as the documents are not written by the user. It's also possible to convert yaml documents to json at the python package build time, so the we wouldn't actually need yaml parser for schema files. Although, grader configuration is still yaml.

[markkuriekkinen]

A quick hotfix for removing the warnings might be to ignore the warnings of this type in the Python command-line parameters: python -Wignore UserWarning
https://docs.python.org/3/using/cmdline.html#cmdoption-w

I haven't tried if it works.

The python command-line arguments could be added to the grade-python container:
https://github.com/apluslms/grade-python/blob/480365bbeeb5dd29cc21db74191f53be06d0f154/bin/_graderutils_exec#L2

[raphendyr]

It might be a good idea to only ignore these specific warnings. Something to look into:

• https://docs.python.org/3/library/warnings.html#warnings.filterwarnings
• https://docs.python.org/3/library/warnings.html#warnings.catch_warnings (an example how to suppress warnings)

[markkuriekkinen]

PR #34 suppresses the UserWarnings.