Annotations

Autowiring relies on annotations or hints to be able to inject dependencies. When it is not possible to automatically locate a given dependency, it must be annotated with additional metadata.

When do you need to provide annotations.

Injecting	Annotations required?	What is required
Services	No
Interface with only one implementation	No
Default implementation of an interface	No
Interface with multiple implementations	Yes	Qualifier
Parameters	Yes	Parameter name
Parameter expressions	Yes	Expression

Annotation types

Wireup supports two types of annotations. Using Python's Annotated and default values.

Annotated

This is the preferred method for Python 3.9+ and moving forward. It is also recommended to backport this using typing_extensions for Python 3.8.

@container.autowire
def target(
    env: Annotated[str, Inject(param="env_name")],
    logs_cache_dir: Annotated[str, Inject(expr="${cache_dir}/logs")],
):
    ...

Default values (deprecated)

This relies on the use of default values to inject parameters. Anything that can be passed to Annotated may also be used here.

@container.autowire
def target(
    env: str = Inject(param="env_name"), 
    logs_cache_dir: str = Inject(expr="${cache_dir}/logs")
):
    ...

Explicit injection annotation

Even though annotating services is optional, you CAN still annotate them to be explicit about what will be injected. This also has the benefit of making the container throw when such as service does not exist instead of silently skipping this parameter.

This has limited application when using annotated types as the runtime will raise regardless, but when using default values as annotations it can be quite useful.

@container.autowire
def target(random_service: Annotated[RandomService, Inject()]):
    ...