environment_variable_descriptor.py

class EnvironmentVariable:
    """A descriptor that helps fetching environment variables.

    To be used like

        class Environment:
            LOG_LEVEL = EnvironmentVariable(default="INFO")
            CONFIG_PATH = EnvironmentVariable(is_required=True)


    Then you can do:
        env = Environment()
        env.LOG_LEVEL   # will get the environment variable, or the default it not set
        env.CONFIG_PATH # Will get the value from the environment variable, or fail if not set
    """

    def __init__(self, is_required: bool = False, default: str | None = None) -> None:
        self.name = None
        self.is_required = is_required
        self._default = default

    def __get__(self, instance, owner):
        return self.get()

    def __set_name__(self, owner, name):
        self.name = name

    def get(self) -> str:
        value = os.getenv(self.name)
        if not value and self.is_required:
            self.fail()
        if not value and self._default is None:
            self.fail()
        return str(value) or self._default

    def is_set(self) -> bool:
        return bool(os.getenv(self.name) or self._default)

    def fail(self):
        logger.error("Missing required environment variable: %r", self.name)
        raise ValueError(f"{self.name!r} is not set")