flasklet

A few nice things for Flask: typed flash messages, convention-based blueprint auto-discovery, route auto-importing, and helpers for rendering partials, blocks, and macros from Python.

Typed configuration

flasklet.config gives Flask apps a typed, environment-backed settings object instead of untyped app.config dict lookups.

from flasklet import config


class Settings(config.Config, prefix="BOXMINDER_"):
	base_url: str = config.from_env(default="/")
	flush_interval_seconds: int = config.from_env(default=60)


def create_app() -> Flask:
	app = Flask(__name__)
	settings = config.load(Settings)
	config.init_app(app, settings, flask_keys={"APPLICATION_ROOT": "base_url"})
	return app

A field's variable name defaults to the field name uppercased, prefixed with the class-level prefix (here BOXMINDER_BASE_URL and BOXMINDER_FLUSH_INTERVAL_SECONDS). Pass a name to from_env to override it. The prefix is inherited by subclasses. load(Settings, prefix=...) prepends a further prefix at load time.

load reads the environment when called (inside the app factory, not at import time) and converts values to the field's declared type: str, int, float, bool, Path, Optional[T], list[T], and NewType wrappers. A bool accepts only the exact strings true and false; a list is split on commas, with an empty variable meaning the empty list. A required field with a missing variable, or a value that cannot be converted, raises with the offending variable named.

Settings derived from other settings are declared with derived. They are computed once when the object is built, in declaration order, so a derived field may read earlier ones. They are not constructor arguments.

class Settings(config.Config, prefix="BOXMINDER_"):
	data_dir: Path | None = config.from_env(default=None)
	base_dir: Path = config.derived(lambda s: (s.data_dir or PROJECT_ROOT).resolve())
	db_uri: str = config.derived(lambda s: f"sqlite:///{s.base_dir / 'db.sqlite3'}")

Request-time access is typed through the generic read_config, passing the settings class:

config.read_config(Settings).base_url