Annotations

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

Note

Although using annotations is recommended, they are entirely optional. For more info see: Manual Configuration.

When do you need to provide annotations.

Injecting	Annotations required?	What is required
Services	No
Interface with only one implementation	No
Interface with multiple implementations	Yes	Qualifier
Parameters	Yes	Parameter name
Parameter expressions	Yes	Parameter expression

Annotation types

Wireup supports two types of annotations. Using Python's Annotated or by using 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, Wire(param="env_name")],
    logs_cache_dir: Annotated[str, Wire(expr="${cache_dir}/logs")],
):
    ...

Default values

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 = wire(param="env_name"), 
    logs_cache_dir: str = wire(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.

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