pydantic/docs/examples/settings_add_custom_source.py

import json
from pathlib import Path
from typing import Dict, Any

from pydantic import BaseSettings


def json_config_settings_source(settings: BaseSettings) -> Dict[str, Any]:
    """
    A simple settings source that loads variables from a JSON file
    at the project's root.

    Here we happen to choose to use the `env_file_encoding` from Config
    when reading `config.json`
    """
    encoding = settings.__config__.env_file_encoding
    return json.loads(Path('config.json').read_text(encoding))


class Settings(BaseSettings):
    foobar: str

    class Config:
        env_file_encoding = 'utf-8'

        @classmethod
        def customise_sources(
            cls,
            init_settings,
            env_settings,
            file_secret_settings,
        ):
            return (
                init_settings,
                json_config_settings_source,
                env_settings,
                file_secret_settings,
            )


print(Settings())