ididi 1.0.5

A dependency injection library for Python, Optimized for serverless applications

Ididi

Genius simplicity, unmatched power

ididi is 100% test covered and strictly typed.

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Documentation: https://raceychan.github.io/ididi

Source Code: https://github.com/raceychan/ididi

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Install

pip install ididi

To view viusal dependency graph, install graphviz

pip install ididi[graphviz]

Usage

Quick Start

import ididi

class UserService:
    def __init__(self, repo: UserRepository):
        self.repo = repo

user_service = ididi.resolve(UserService) 

No Container, No Provider, No Wiring, just Python

Features

[!TIP] Ididi has a compact codebase with core part being < 600 LOC, feature requests, pull requests and issues are all welcome and appreciated.

Automatic dependencies injection

You can use generator/async generator to create a resource that needs to be closed. NOTE:

1. resources, if set to be reused, will be shared across different dependents only within the same scope, and destroyed when the scope is exited.
2. async resource in a sync dependent is not supported, but sync resource in a async dependent is supported.

from ididi import DependencyGraph

dg = DependencyGraph()

@dg.node
async def get_db(client: Client) -> ty.AsyncGenerator[DataBase, None]:
    db = DataBase(client)
    assert client.is_opened
    try:
        await db.connect()
        yield db
    finally:
        await db.close()

@dg.entry
async def main(db: DataBase, sql: str) -> ty.Any:
    res = await db.execute(sql)
    return res

assert await main(sql="select money from bank")

[!NOTE] DependencyGraph.node accepts a wide arrange of types, such as dependent class, sync/async facotry, sync/async resource factory, with typing support.

Using Scope to manage resources

• Infinite nested scope is supported.

• Parent scope can be accssed by child scope(within the same context)

• Resources will be shared across dependents only withint the same scope(reuse needs to be True)

• Resources will be automatically closed and destroyed when the scope is exited.

• Classes that implment contextlib.AbstractContextManager or contextlib.AbstractAsyncContextManager are also considered to be resources and can/should be resolved within scope.

• Scopes are separated by context

[!NOTE] If you have two call stack of a1 -> b1 and a2 -> b2, Here a1 and a2 are two calls to the same function a, then, in b1, you can only access scope created by the a1, not a2.

This is particularly useful when you try to separate resources by route, endpoint, request, etc.

Async, or not, works either way

@dg.node
def get_resource() -> ty.Generator[Resource, None, None]:
    res =  Resource()
    yield res
    res.close()

with dg.scope() as scope:
    resource = scope.resolve(Resource)

# For async generator
async with dg.scope() as scope:
    resource = await scope.resolve(Resource)

Contexted Scope

You can use dg.use_scope to retrive most recent scope, context-wise, this allows your to have access the scope without passing it around, e.g.

async def service_factory():
    async with dg.scope() as scope:
        service = scope.resolve(Service)
        yield service

@app.get("users")
async def get_user(service: Service = Depends(dg.factory(service_factory)))
    await service.create_user(...)

Then somewhere deep in your service.create_user call stack

async def create_and_publish():
    uow = dg.use_scope().resolve(UnitOfWork)
    async with uow.trans():
        user_repo.add_user(user)
        event_store.add(user_created_event)

Here dg.use_scope() would return the same scope you created in your service_factory.

Named Scope

You can create infinite level of scopes by assigning hashable name to scopes

# at the top most entry of a request
async with dg.scope(request_id) as scope:
    ...

now scope with name request_id is accessible everywhere within the request context

request_scope = dg.use_scope(request_id)

[!NOTE] Two scopes or more with the same name would follow most recent rule.

Nested Nmaed Scope

async with dg.scope(app_name) as app_scope:
    async with dg.scope(router) as router_scope:
        async with dg.scope(endpoint) as endpoint_scope:
            async with dg.scope(user_id) as user_scope:
                async with dg.scope(request_id) as request_scope:
                    ...

For any functions called within the request_scope, you can get the most recent scope with dg.use_scope(), or its parent scopes, i.e. dg.use_scope(app_name) to get app_scope.

Tutorial

There are cases where you would like to menually build the dependency yourself with a factory function,

Usage with FastAPI

from fastapi import FastAPI
from ididi import DependencyGraph

app = FastAPI()
dg = DependencyGraph()

def auth_service_factory() -> AuthService:
    async with dg.scope() as scope
        yield dg.resolve(AuthService)

Service = ty.Annotated[AuthService, Depends((auth_service_factory))]

@app.get("/")
def get_service(service: Service):
    return service

[!IMPORTANT] DependencyGraph does NOT have to be a global singleton

Although we use dg extensively to represent an instance of DependencyGraph for the convenience of explaination, it DOES NOT mean it has to be a global singleton. These are some examples you might inject it into your fastapi app at different levels.

(ididi v1.0.5) You can create different dependency graphs in different files, then merge them in the main graph

from app.features.user import user_graph
from app.features.auth import auth_graph
from app.features.payment import payment_graph

# in your entry file

dg = DependencyGraph()
dg.merge([user_graph, auth_graph, payment_graph])

DependencyGraph as an app-level instance

import typing as ty

from fastapi.routing import APIRoute, APIRouter
from starlette.types import ASGIApp, Receive, Scope, Send

from ididi import DependencyGraph


class GraphedScope(ty.TypedDict):
    dg: DependencyGraph


@asynccontextmanager
async def lifespan(app: FastAPI | None = None) -> ty.AsyncIterator[GraphedScope]:
    async with DependencyGraph() as dg:
        yield {"dg": dg}


@app.post("/users")
async def signup_user(request: Request):
    dg = request.state.dg
    service = dg.resolve(UserService)
    user_id = await service.signup_user(...)
    return user_id

Injecting DependencyGraph at route level

class UserRoute(APIRoute):
    def get_route_handler(self) -> ty.Callable[[Request], ty.Awaitable[Response]]:
        original_route_handler = super().get_route_handler()

        async def custom_route_handler(request: Request) -> Response:

            dg = DependencyGraph()
            request.scope["dg"] = dg

            async with dg.scope() as user_scope:
                response = await original_route_handler(request)
                return response

        return custom_route_handler

user_router = APIRouter(route_class=UserRoute)

Injecting DependencyGraph at request level

class GraphedMiddleware:
    def __init__(self, app, dg: DependencyGraph):
        self.app = app
        self.dg = dg

    async def __call__(self, scope: Scope, receive: Receive, send: Send):
        # NOTE: remove follow three lines would break lifespan
        # as startlette would pass lifespan event here
        if scope["type"] != "http":
            await self.app(scope, receive, send)
            return

        scope["dg"] = self.dg
        await self.app(scope, receive, send)


app.add_middleware(GraphedMiddleware, dg=DependencyGraph)

with background task

To use scope in background task, you would need to explicitly pass scope to your task

@app.post("/send-notification/{email}")
async def send_notification(email: str, background_tasks: BackgroundTasks):
    background_tasks.add_task(write_notification, dg.use_scope(), email, message="some notification")
    return {"message": "Notification sent in the background"}

def write_notification(scope: SyncScope, email: str, message=""):
    with open("log.txt", mode="w") as email_file:
        content = f"notification for {email}: {message}"
        email_file.write(content)
        scope.resolve(MessageQueue).publish("Email Sent")

    # To search parent scope:
    parent_scope = scope.get_scope(name)

Usage of factory

If you are working with non-trivial web application, there is a good chance that you already have some factory functions used to build your dependnecies, to get them work with ididi, just decorate them with dg.node.

• Menually config details of external libraries

@dg.node
def engine_factory(config: Config)-> sqlalchemy.engine.Engine:
    engine = create_engine(
        url=config.db.URL,
        pool_recycle=config.db.POOL_RECYCLE,
        isolation_level=config.db.ISOLATION_LEVEL
    )
    return engine

• Privide a stub for your dependencies for testing.

@dg.node
def fake_engine_factory(config: Config)-> sqlalchemy.engine.Engine:
    return FakeEngine()

@pytest.fixture
def engine():
    return dg.resolve(Engine)

• Provide different implementation of the dependencies based on some condition.

@dg.node
def redis_cache(config: Config) -> redis.Redis:
    if config.RUNTIME_ENV == 'prod':
        return redis.Redis(...)
    return redis.Redis(...)

• Assign a implementation for parent class

class Storage:
    ...
class Database(Storage):
    ...
class S3(Storage): 
    ...

@dg.node
def storage_factory(config: Config) -> Storage:
    if config.storage.storage_type = "cold":
        return S3(...)
    return Database(...)

This works for ABC, typing.Protocol, as well as plain classes.

Visualize the dependency graph(beta)

from ididi import DependencyGraph, Visualizer
dg = DependencyGraph()

class ConfigService:
    def __init__(self, env: str = "test"):
        self.env = env


class DatabaseService:
    def __init__(self, config: ConfigService):
        self.config = config


class CacheService:
    def __init__(self, config: ConfigService):
        self.config = config


class BaseService:
    def __init__(self, db: DatabaseService):
        self.db = db


class AuthService(BaseService):
    def __init__(self, db: DatabaseService, cache: CacheService):
        super().__init__(db)
        self.cache = cache


class UserService:
    def __init__(self, auth: AuthService, db: DatabaseService):
        self.auth = auth
        self.db = db


class NotificationService:
    def __init__(self, config: ConfigService):
        self.config = config


class EmailService:
    def __init__(self, notification: NotificationService, user: UserService):
        self.notification = notification
        self.user = user

dg.static_resolve(EmailService)
vs = Visualizer(dg)
vs.view # use vs.view in jupyter notebook, or use vs.save(path, format) otherwise
vs.save(path, format)

Circular Dependency Detection

ididi would detect if circular dependency exists, if so, ididi would give you the circular path

For example:

class A:
    def __init__(self, b: "B"):
        self.b = b


class B:
    def __init__(self, a: "C"):
        self.a = a


class C:
    def __init__(self, d: "D"):
        pass


class D:
    def __init__(self, a: A):
        self.a = a


def test_advanced_cycle_detection():
    """
    DependentNode.resolve_forward_dependency
    """
    dag = DependencyGraph()

    with pytest.raises(CircularDependencyDetectedError) as exc_info:
        dag.static_resolve(A)
    assert exc_info.value.cycle_path == [A, B, C, D, A]

You can call DependencyGraph.static_resolve_all on app start to statically resolve all your noded classes, and let ididi get ready for resolve them at upcoming calls.

Lazy Dependency(Beta)

you can use @dg.node(lazy=True) to define a dependent as lazy, which means each of its dependency will not be resolved untill accessed.

start with v0.3.0, lazy node is no longer transitive.

class UserRepo:
    def __init__(self, db: Database):
        self._db = db

    def test(self):
        return "test"

@dg.node(lazy=True)
class ServiceA:
    def __init__(self, user_repo: UserRepo, session_repo: SessionRepo):
        self._user_repo = user_repo
        self._session_repo = session_repo

        assert isinstance(self._user_repo, LazyDependent)
        assert isinstance(self._session_repo, LazyDependent)

    @property
    def user_repo(self) -> UserRepo:
        return self._user_repo

    @property
    def session_repo(self) -> SessionRepo:
        return self._session_repo

assert isinstance(instance.user_repo, LazyDependent)
assert isinstance(instance.session_repo, LazyDependent)

# user_repo would be resolved when user_repo.test() is called.
assert instance.user_repo.test() == "test" 

Runtime override

dg = DependencyGraph()

class Inner:
    def __init__(self, value: str = "inner"):
        self.value = value

@dg.node
class Outer:
    def __init__(self, inner: Inner):
        self.inner = inner

# Override nested dependency
instance = dg.resolve(Outer, inner=Inner(value="overridden"))
assert instance.inner.value == "overridden"

Error context

static resolve might fail when class contain unresolvable dependencies, when failed, ididi would show a chain of errors like this:

ididi.errors.MissingAnnotationError: Unable to resolve dependency for parameter: env in <class 'Config'>,
annotation for `env` must be provided

<- Config(env: _Missed)
<- DataBase(config: Config)
<- AuthService(db: DataBase)
<- UserService(auth: AuthService)

Where UserService depends on AuthService, which depends on Database, then Config, but Config.env is missing annotation.

To solve error like this, you can either provide the missing annotation, or you can provide a factory method with menually provide the value.

@dg.node
def config_factory() -> Config:
    return Config(env=".env")

this is more common when you want to menually config external libraries like redis, sqlalchemy, etc.

@dg.node
def redis_factory(config: Config) -> redis.Redis:
    return Redis(url=config.redis_url)