Annotations

WireUp relies on various kind of type annotations or hints to be able to autowire dependencies. When it is not possible to automatically locate a given dependency the argument must be annotated with additional metadata.

When do you need to provide annotations.

Optional when injecting:

• Services
• Injecting an interface which has only one implementing service

Required when injecting:

• Parameters
• Parameter expressions
• Injecting an interface which has multiple implementing services.

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()]):
    ...