ididi 1.5.1

A dependency injection library for Python, Optimized for serverless applications

Ididi

Genius simplicity, unmatched power

ididi is 100% test covered and strictly typed.

---

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

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

---

Install

ididi requires python >= 3.9

pip install ididi

To view viusal dependency graph, install graphviz

pip install ididi[graphviz]

Features

• Powerful: Ididi does what alternatives do, and also provides features that others don't.
• Performant: almost as fast as hard-coded factories, one of the fastest dependency injection framework available.
• Noninvasive: No / minial changes to your existing code
• Smart: inject dependency based on type hints, with strong support to typing module.
• Correct, strictly typed, well-organized exceptions, well-formatted and detail-rich error messages

TypingSupport

ididi has strong support to typing module, includes:

• TypedDict
• Unpack
• NewType
• Annotated
• Literal
• Optional
• Union

...and more.

Check out tests/features/test_typing_support.py for examples.

Usage

Quick Start

from typing import AsyncGenerator
from ididi import use, entry

async def conn_factory(engine: AsyncEngine) -> AsyncGenerator[AsyncConnection, None]:
    async with engine.begin() as conn:
        yield conn

class UnitOfWork:
    def __init__(self, conn: AsyncConnection=use(conn_factory)):
        self._conn = conn

@entry
async def main(command: CreateUser, uow: UnitOfWork):
    await uow.execute(build_query(command))

# note uow is automatically injected here
await main(CreateUser(name='user'))

To resolve AsyncConnection outside of entry function

from ididi import Graph

dg = Graph()

async with dg.ascope():
    conn = await scope.resolve(conn_factory)

Key Concepts

Marks

ididi provides two marks, use and Ignore, they are convenient shortcut for Graph.node. Technically, they are just metadata carried by typing.Annotated, and should work fine with other Annotated metadata.

use

You can use Graph.node to register a dependent with its factory, here we register dependent Database with its factory db_factory. This means whenver we call dg.resolve(Database), db_factory will be call.

def db_factory() -> Database:
    return Database()

dg = Graph()
dg.node(db_factory)

Alternatively, you can annotate it inside __init__, this allow you to instantiate Graph in a lazy manner.

from ididi import use
class Repository:
    def __init__(self, db: Annotated[Database, use(db_factory)]):
        ...

Ignore

ididi takes a "resolve by default" approach, for dependencies you would like ididi to ignore, you can config ididi to ignore them.

• Ignore at Graph level

from datetime import datetime
from pathlib import Path

dg = Graph(ignore=(datetime, Path))

• Ignore at Node level

dg = Graph()
class Clock:
    def __init__(self, dt: datetime): ...

dg.node(Clock, ignore=datetime)

Alternatively, you can mark a dependency using ididi.Ignore,

from ididi import Ignore

class Clock:
    def __init__(self, dt: Ignore[datetime]): ...

Function dependency

Declear a function as a dependency by using Ignore to annotate its return type.

@dataclass
class User:
    name: str
    role: str

def get_user(config: Config) -> Ignore[User]:
    assert isinstance(config, Config)
    return User("user", "admin")

def validate_admin(
    user: Annotated[User, use(get_user)], service: UserService
) -> Ignore[str]:
    assert user.role == "admin"
    assert isinstance(service, UserService)
    return "ok"

class Route:
    def __init__(self, validte_permission: Annotated[str, use(validate_admin)]):
        assert validte_permission == "ok"

assert dg.resolve(validate_admin) == "ok"
assert isinstance(dg.resolve(Route), Route)

Since get_user returns Ignore[User] instead of User, it won't be used as factory to resolve User.

Dependency factory

from ididi import use
from typing import NewType
from datetime import datetime, timezone

UserID = NewType("UserID", str)

def utc_factory() -> datetime:
    return datetime.now(timezone.utc)

def user_id_factory() -> UserID:
    return UserID(str(uuid4()))

class User:
    def __init__(self, user_id: UserID, created_at: Annotated[datetime, use(utc_factory)]):
        self.user_id = user_id
        self.created_at = created_at

user = ididi.resolve(User)
assert user.created_at.tzinfo == timezone.utc

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

Scope

Scope is a temporary view of the graph specialized for handling resources.

In a nutshell:

• Scope can access(read-only) registered singletons and resolved instances of its parent graph
• Dependents registered/resolved in a scope will stay in the scope.
• its parent graph can't access its registered singletons and resolved resources.

Using Scope to manage resources

• Infinite number of nested scope
• Parent scope can be accssed by its child scopes(within the same context)
• Resources will be shared across dependents only withint the same scope
• Resources will be automatically closed 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

[!TIP] 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 scope

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

@dg.node
async def get_asyncresource() -> ty.Generator[AsyncResource, None, None]:
    res = AsyncResource()
    async with res:
        yield res


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

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

[!TIP] dg.node will leave your class/factory untouched, i.e., you can use it as a function. e.g. dg.node(get_resource, reuse=False)

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.ascope() as scope:
        service = scope.resolve(Service)
        yield service

@app.get("users")
async def get_user(service: Service = Depends(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.ascope(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 or more scopes with the same name would follow most recent rule.

Nested Nmaed Scope

async with dg.ascope(app_name) as app_scope:
    async with dg.ascope(router_name) as router_scope:
        async with dg.ascope(endpoint_name) as endpoint_scope:
            async with dg.ascope(user_id) as user_scope:
                async with dg.ascope(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.

Testing

Override class dependency resolution

You can control how ididi resolve a dependency during testing, by register the test double of the dependency using

• Graph.override
• entry.replace

Example: For the following dependent

class UserRepository:
    def __init__(self, db: DataBase):
        self.db=db

dg = Graph()
assert isinstance(dg.resolve(UserRepository).db, DataBase)

in you test file,

class FakeDB(DataBase): ...

def db_factory() -> DataBase:
    return FakeDB()


def test_resolve():
    dg = Graph()
    assert isinstance(dg.resolve(db_factory).db, DataBase)

    dg.override(DataBase, db_factory)
    assert isinstance(dg.resolve(UserRepository).db, FakeDB)

Use Graph.override to replace DataBase with its test double.

Override entry dependency resolution

async def test_entry_replace():
    @ididi.entry
    async def create_user(
        user_name: str, user_email: str, service: UserService
    ) -> UserService:
        return service

    class FakeUserService(UserService): ...

    create_user.replace(UserService, FakeUserService)

    res = await create_user("user", "[e-mail]")
    assert isinstance(res, FakeUserService)

Use entryfunc.replace to replace a dependency with its test double.

Graph.override vs entry.replace

Graph.override applies to the whole graph, entry.replace applies to only the entry function.

More

For more detailed information, check out Documentation

• Tutorial

• Usage of factory

• Visualize the dependency graph

• Circular Dependency Detection

• Error context