Getting Started

To showcase the basics of Wireup, we will create a container able to inject the following:

• A WeatherService that queries a fictional weather api. It needs an api key, a KeyValueStore to cache data and an async http client to make requests.
• KeyValueStore itself needs a redis_url denoting the server it will connect to to query/store data.

These services will then be retrieved in a /weather/forecast endpoint that requires WeatherService to provide weather information.

graph LR
    redis_url[⚙️ redis_url] --> KeyValueStore[🐍 KeyValueStore]
    weather_api_key[⚙️ weather_api_key] --> WeatherService
    KeyValueStore --> WeatherService[🐍 WeatherService]
    WeatherService --> Route[🌎 /weather/forecast]
    F[🏭 HttpClient] --> WeatherService

Tip

There will be little + icons in code fragments. You can click on those for more detailed information as to what is happening in that particular line.

1. Setup

Install wireup using pip or your favorite package manager.

$ pip install wireup

The first step is to create a container.

container.py

import wireup

container = wireup.create_async_container(
    # Parameters are an optional key-value configuration store.
    # You can inject parameters as necessary by their name where required.
    parameters={ # (1)!
        "redis_url": os.environ["APP_REDIS_URL"],
        "weather_api_key": os.environ["APP_WEATHER_API_KEY"],
    },
    # Let the container know where service registrations are located.
    # This is a list of top-level modules Wireup should scan for service declarations.
    service_modules=[services]  # (2)!
)

1. Parameters are configuration your application needs. Such as an api key, database url, or other settings.

   You can inject them as necessary by their name (dict key) where required. Wireup won't pull things from the environment or other places for you. You need to expose to it the different settings you'll need.

   You don't have to use this if you prefer using things like pydantic-settings, but it will enable you to have self-contained service definitions without writing additional set-up code to create these objects.

   Note that the values can be literally anything you need to inject and not just int/strings or other scalars. You can put dataclasses for example in the parameters to inject structured configuration.

2. Service modules is a list of top-level python modules containing service definitions this container needs to know about (Classes or functions decorated with @service or @abstract.). The container will only create types that are explicitly registered with it.

Container variants: Sync and Async

Wireup includes two types of containers: async and sync. The difference is that the async one exposes async def methods for the common operations and is capable of creating resources from async def factories.

The async container can create both regular and resources from async factories.

If you don't use async in your code you should create a container via wireup.create_sync_container. Some integrations that Wireup provides also require you to create containers of a given type. E.g: FastAPI integration only supports async containers.

Read: Global variables

Using this approach means relying on global state, which ties your application to a single container instance. This might be sufficient for you and that's okay but, if you want to avoid global state, it's better to create the container within your application factory and store it in your application's state instead.

2. Define services

The container uses types and annotations to define services and the discover dependencies between them. This results in self-contained service declarations without having to create factories for every service.

🐍 KeyValueStore

To create KeyValueStore, all we need is the redis_url parameter. The @service decorator tells Wireup this is a service, and we need to tell the container via annotated types to fetch the value of the redis_url parameter for dsn.

services/key_value_store.py

from wireup import service, Inject
from typing_extensions import Annotated

@service  #(1)!
class KeyValueStore:
    def __init__(self, dsn: Annotated[str, Inject(param="redis_url")]) -> None:  #(2)!
        self.client = redis.from_url(dsn)

1. Decorators are only used to collect metadata. This makes testing simpler, as you can still instantiate this like a regular class in your tests.
2. Since type-based injection is not possible here (there can be many string/int parameters after all), parameters must be annotated with the Inject(param=name) syntax. This tells the container which parameter to inject.

🏭 aiohttp.ClientSession

The http client making requests cannot be instantiated directly as we need to enter an async context manager. To accommodate such cases, Wireup allows you to use functions to create dependencies. These can be sync/async as well as regular or generator functions if cleanup needs to take place.

Factories can define their dependencies in the function's signature.

When using generator factories make sure to call container.close when the application is terminating for the necessary cleanup to take place.

services/factories.py

@service
async def make_http_client() -> AsyncIterator[aiohttp.ClientSession]:
    async with aiohttp.ClientSession() as client:
        yield client

🐍 WeatherService

Creating WeatherService is also straightforward. The @service decorator is used to let Wireup know this is a service and we use the same syntax as above for the api_key.

Class dependencies do not need additional annotations, even though the http client is created via an async generator. This is transparently handled by the container.

services/weather_service.py

@service
class WeatherService:
    def __init(
        self,
        api_key: Annotated[str, Inject(param="weather_api_key")], #(1)!
        kv_store: KeyValueStore, #(2)!
        client: aiohttp.ClientSession, #(3)!
    ) -> None: ...

1. Same as above, weather api key needs the parameter name for the container to inject it.
2. KeyValueStore can be injected only by type and does not require annotations.
3. aiohttp.ClientSession can be injected only by type and requires no additional configuration.

3. Use

All that's left now is to retrieve services from the container.

Service LocatorInjection via decoratorFastAPIFlaskDjango

To fetch services from the container, call .get on the container instance with the type you wish to retrieve.

views/posts.py

@app.get("/weather/forecast")
async def get_forecast():
    weather_service = await container.get(WeatherService)
    return await weather_service.get_forecast(...)

You can also apply Wireup containers as decorators. See Apply the container as a decorator docs for more info, but the end result is that you can decorate any function and specify dependencies to inject in it's signature.

views/posts.py

from wireup import Injected, inject_from_container

@app.get("/weather/forecast")
@inject_from_container(container)
async def get_forecast(weather_service: Injected[WeatherService]):
    return await weather_service.get_forecast(...)

With the FastAPI integration you can just declare dependencies in http or websocket routes.

views/posts.py

from wireup import Injected

@app.get("/weather/forecast")
async def get_forecast(weather_service: Injected[WeatherService]):
    return await weather_service.get_forecast(...)

Learn More: FastAPI Integration.

With the Flask integration you can just declare dependencies in views.

views/posts.py

from wireup import Injected

@app.get("/weather/forecast")
async def get_forecast(weather_service: Injected[WeatherService]):
    return await weather_service.get_forecast(...)

Learn More: Flask Integration.

With the Django integration you can just declare dependencies in views. The integration provides support for async views, regular views as well as class-based views.

views/posts.py

from wireup import Injected

async def get_forecast(weather_service: Injected[WeatherService]):
    return await weather_service.get_forecast(...)

Learn More: Django Integration.

3.5 Integrate

While Wireup is framework-agnostic, usage can be simplified when using it alongside one of the integrations. Key benefits of the integrations are:

• Automatic injection in routes without having to do container.get or use decorators.
• Lifecycle management and access to request-scoped dependencies.
• Eliminates the need for a global container variable as containers are bound to the application instance.
• Other goodies specific for that particular framework.

Integrations

• Django
• FastAPI
• Flask

4. Test

Wireup does not patch your services, which means they can be instantiated and tested independently of the container.

To substitute dependencies on targets such as views in a web application you can override dependencies with new ones on the fly.

with container.override.service(WeatherService, new=test_weather_service):
    response = client.get("/weather/forecast")

Requests to inject WeatherService during the lifetime of the context manager will result in test_weather_service being injected instead.

Conclusion

This concludes the "Getting Started" walkthrough, covering the most common dependency injection use cases.

Info

• Wireup can perform injection on both sync and async targets.
• If you need to create multiple containers, every container you create is separate from the rest and has its own state.

Next Steps

• Services
• Parameters
• Factory functions