philiprehberger-di

Lightweight dependency injection container for Python.

Installation

pip install philiprehberger-di

Usage

from philiprehberger_di import Container

container = Container()
container.register(Logger)
logger = container.resolve(Logger)

Singletons

container.register(Database, singleton=True)

a = container.resolve(Database)
b = container.resolve(Database)
assert a is b

Custom Factories

container.register(Cache, factory=lambda: Cache(max_size=256))
cache = container.resolve(Cache)

Recursive Resolution

class Service:
    def __init__(self, db: Database, logger: Logger) -> None:
        self.db = db
        self.logger = logger

container.register(Database)
container.register(Logger)
container.register(Service)
service = container.resolve(Service)  # db and logger are injected automatically

Inject Decorator

from philiprehberger_di import Container, inject

container = Container()
container.register(Logger, singleton=True)

@inject(container)
def handle_request(logger: Logger) -> str:
    logger.log("request handled")
    return "ok"

handle_request()  # logger is resolved and injected automatically

Lifecycle Hooks

container.register(
    Database,
    singleton=True,
    on_create=lambda db: db.connect(),
    on_destroy=lambda db: db.disconnect(),
)

db = container.resolve(Database)  # on_create called after creation
container.reset()                 # on_destroy called before clearing singletons

Circular Dependency Detection

The container detects circular dependencies during resolution and raises a CircularDependencyError with the full dependency chain:

from philiprehberger_di import CircularDependencyError

class A:
    def __init__(self, b: B) -> None: ...

class B:
    def __init__(self, a: A) -> None: ...

container.register(A)
container.register(B)

try:
    container.resolve(A)
except CircularDependencyError as e:
    print(e)  # Circular dependency detected: A -> B -> A
    print(e.chain)  # [A, B, A]

Scoped Lifetime

Services registered with Lifetime.SCOPED are singletons within a scope but differ across scopes:

from philiprehberger_di import Container, Lifetime

container = Container()
container.register(RequestContext, lifetime=Lifetime.SCOPED)
container.register(Logger, lifetime=Lifetime.SINGLETON)

with container.create_scope() as scope:
    ctx1 = scope.resolve(RequestContext)
    ctx2 = scope.resolve(RequestContext)
    assert ctx1 is ctx2  # same within the scope

# on_destroy hooks are called when the scope exits

Lazy Resolution

Defer construction of an expensive service until first use:

from philiprehberger_di import Container, Lifetime

container = Container()
container.register(ExpensiveClient, lifetime=Lifetime.SINGLETON)

proxy = container.lazy(ExpensiveClient)
# ExpensiveClient is NOT yet constructed

result = proxy.do_thing()  # constructed on first access, cached afterwards

Introspection

Check whether a type is registered, or remove it. Useful when wiring up tests:

container.is_registered(Database)  # True / False

container.register(Database, singleton=True)
container.unregister(Database)     # also clears cached singleton + calls on_destroy

API

Function / Class	Description
Container()	Create a new dependency injection container
container.register(cls, factory?, singleton?, lifetime?, on_create?, on_destroy?)	Register a class with optional factory, lifetime, and lifecycle hooks
container.unregister(cls)	Remove a registration; clears any cached singleton and calls on_destroy
container.is_registered(cls)	Return whether cls is registered in this container
container.resolve(cls)	Resolve an instance, recursively injecting dependencies
container.lazy(cls)	Return a Lazy[cls] proxy that resolves on first use
container.create_scope()	Create a child scope for scoped lifetime management
container.reset()	Call on_destroy for singletons with hooks, then clear the cache
inject(container)	Decorator that resolves type-hinted params from the container
Lifetime.TRANSIENT	New instance on every resolve (default)
Lifetime.SINGLETON	Single shared instance across the container
Lifetime.SCOPED	Single instance per scope, transient without a scope
CircularDependencyError	Raised when a circular dependency chain is detected
Scope	Child scope returned by create_scope(), used as a context manager
Lazy[T]	Proxy that resolves the underlying service on first access

Development

pip install -e .
python -m pytest tests/ -v

Support

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License

MIT