Injection

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Easy dependency injection for all, works with Python 3.8-3.12. Main features and advantages:

  • support Python 3.8-3.12;

  • works with FastAPI, Litestar, Flask and Django REST Framework;

  • support dependency injection via Annotated in FastAPI;

  • the code is fully typed and checked with mypy;

  • no third-party dependencies;

  • support async injections;

  • no wiring;

  • the life cycle of objects (scope) is implemented by providers;

  • overriding dependencies for testing;

  • 100% code coverage;

  • good documentation;

  • intuitive and almost identical api with dependency-injector, which will allow you to easily migrate to injection (see migration from dependency injector);

Installation

pip install deps-injection

Compatibility between web frameworks and injection features

Framework

Dependency injection with @inject

Overriding providers

Dependency injection with @autoinject

FastAPI

✅

✅

➖

Flask

✅

✅

✅

Django REST Framework

✅

✅

✅

Litestar

✅

✅

➖

Using example with FastAPI and SQLAlchemy

from contextlib import contextmanager
from random import Random
from typing import Annotated, Any, Callable, Dict, Iterator

import pytest
from fastapi import Depends, FastAPI
from sqlalchemy import create_engine, text
from sqlalchemy.orm import Session, sessionmaker
from starlette.testclient import TestClient

from injection import DeclarativeContainer, Provide, inject, providers


@contextmanager
def db_session_resource(session_factory: Callable[..., Session]) -> Iterator[Session]:
    session = session_factory()
    try:
        yield session
    except Exception:
        session.rollback()
    finally:
        session.close()


class SomeDAO:
    def __init__(self, db_session: Session) -> None:
        self.db_session = db_session

    def get_some_data(self, num: int) -> int:
        stmt = text("SELECT :num").bindparams(num=num)
        data: int = self.db_session.execute(stmt).scalar_one()
        return data


class DIContainer(DeclarativeContainer):
    db_engine = providers.Singleton(
        create_engine,
        url="sqlite:///db.db",
        pool_size=20,
        max_overflow=0,
        pool_pre_ping=False,
    )

    session_factory = providers.Singleton(
        sessionmaker,
        db_engine.cast,
        autoflush=False,
        autocommit=False,
    )

    db_session = providers.Resource(
        db_session_resource,
        session_factory=session_factory.cast,
        function_scope=True,
    )

    some_dao = providers.Factory(SomeDAO, db_session=db_session.cast)


SomeDAODependency = Annotated[SomeDAO, Depends(Provide[DIContainer.some_dao])]

app = FastAPI()


@app.get("/values/{value}")
@inject
async def sqla_resource_handler_async(
    value: int,
    some_dao: SomeDAODependency,
) -> Dict[str, Any]:
    value = some_dao.get_some_data(num=value)
    return {"detail": value}


@pytest.fixture(scope="session")
def test_client() -> TestClient:
    client = TestClient(app)
    return client


def test_sqla_resource(test_client: TestClient) -> None:
    rnd = Random()
    random_int = rnd.randint(-(10**6), 10**6)

    response = test_client.get(f"/values/{random_int}")

    assert response.status_code == 200
    assert not DIContainer.db_session.initialized
    body = response.json()
    assert body["detail"] == random_int

Introduction

Containers

Providers

Dependency injection

Integration with web frameworks

Testing

Development