Set default values according to JSON schema automatically

Question

I am using the jsonschema package in python to validate my JSONs. I can set default in jsonschema. Let us assume the following schema:

from jsonschema import validate

schema = {
    "type": "object",
    "properties": {
        "key_1": {},
        "key_2": {
            "type": "string",
            "default": "do_not_overwrite_if_key_exists",
        },
        "key_3": {
            "type": "string",
            "default": "use_it_if_key_does_not_exist",
        },
    },
    "required": ["key_1"],
}

json_dict = {"key_1": "key_1_value", "key_2": "key_2_value"}

validate(json_dict, schema)

My json_dict is perfectly valid. I have two questions:

1. Is the default keyword really so "useless" as the documentation (see below) says? This is all you get?

The “default” keyword doesn’t have an effect, but is nice to include for readers of the schema to more easily recognize the default behavior.

2. I would like to have a method that transforms my json_dict into the following according to the default keyword. Do you know of such a package?

json_dict = {"key_1": "key_1_value", "key_2": "key_2_value", "key_3": "use_it_if_key_does_not_exist"}

Thanks!

Answer 1

The default keyword is documented here: https://json-schema.org/draft/2020-12/json-schema-validation.html#rfc.section.9.2

It is indeed not a validation keyword, and only acts as an annotation. It is up to individual applications to decide how to use this annotation when it is generated from schema evaluation.

Answer 2

---- Edited ----

You can use the jsonschema_default package linked below to generate a default JSON object from your JSON schema. https://pypi.org/project/jsonschema-default/

Then you can use the default JSON object to fill in the missing key in your json_dict

Like so:

import jsonschema_default as jd

default_obj = jd.create_from("./data_schema_example.json")

for key in default_obj.keys():
    if key not in json_dict:
        json_dict[key] = default_obj[key]