singletondep

Fully typed dependency management library focusing simplicity and flexibility.

Motivation

This library aims to provide a simple approach to singleton dependency management in projects. In modern live systems, there can be many objects that are expensive and hard to control background tasks, connections, pools life-cycles.

Frameworks either have a very opinionated view on this, or rely on module-level defined objects which may require dynamic parameters that are injected during application startup. This causes module structures to access global variables or importing completely unrelated modules in order to manage singleton dependencies lifecycles applying anti-patterns all around.

This library provides a simple approach to this problem by using simple abstraction over raw functions.

Requirements

python >= 3.10

Installation

pip install singletondep

Usage

from singletondep import singletondep

@singletondep
async def get_db(db_url: str):
    db = Database(settings.db_url)
    await db.connect()
    print("connection established")
    yield db
    await db.disconnect()
    print("disconnected from db")


async def main():
    db_url = "localhost/db_name"
    await get_db.init(db_url)
    # out: connection established
    db = get_db()
    ...
    await get_db.cleanup()
    # out: disconnected from db

This library can be especially useful to manage dependencies in larger projects.

Using as a FastAPI Dependency

import os

from fastapi import FastAPI, APIRouter, Depends
from pydantic import BaseSettings
from singletondep import singletondep
from singletondep.ext.fastapi import register_dep


class Settings(BaseSettings):
    url: str


@singletondep
async def get_db(settings: Settings):
    db = await create_connection(settings.url)
    print("connected to db")
    yield db
    await db.disconnect()
    print("closed db connections")


router = APIRouter()

@router.get("/meaning")
async def get_meaning(db = Depends(get_db)):
    meaning = await db.fetch_meaning()
    return f"the meaning is {meaning}"


def create_app() -> FastAPI:
    app = FastAPI()
    app.include_router(router)
    settings = Settings(url=os.environ["url"])
    register_dep(get_db, app, settings)
    return app