Optional Dependencies

Parameters annotated with T | None or Optional[T] are treated as soft dependencies. If the dependency is not registered, None is injected instead of raising an error.

Constructor Injection

from inversipy import Container

class Cache:
    def get(self, key: str) -> str:
        return f"cached:{key}"

class UserService:
    def __init__(self, cache: Cache | None) -> None:
        self.cache = cache

container = Container()
container.register(UserService)

service = container.get(UserService)
assert service.cache is None  # Cache not registered, so None

When the dependency is registered, it resolves normally:

container.register(Cache)
service = container.get(UserService)
assert isinstance(service.cache, Cache)

In Factory Functions

def create_service(logger: Logger, cache: Cache | None) -> MyService:
    return MyService(logger, cache)

container.register_factory(MyService, create_service)

In container.run()

def my_func(logger: Logger, cache: Cache | None) -> str:
    return f"cache={cache}"

result = container.run(my_func)  # cache=None

Async Resolution

Works identically with get_async() and run_async().

Note

Non-optional parameters that can't be resolved still raise ResolutionError as expected.