outhouse
Because who wants indoor plumbing?
outhouse is a no-nonsense dependency injection provider for Python
applications. In particular, it supports async initialization.
Install
pip install outhouse
Usage
Let's say you want to inject aiohttp's
ClientSession
connection pool into your application. First, tell the framework how to
setup and tear down a ClientSession instance, using the (async) context
manager protocol:
from contextlib import asynccontextmanager
from aiohttp import ClientSession
@asynccontextmanager
async def manage_clientsession():
session = ClientSession()
yield session
await session.close()Then, register this at the dependency provider. The place to keep a
global dependency provider is in the app's global state. For aiohttp,
it works like this:
from outhouse import DependencyProvider
def create_app():
d = DependencyProvider()
d.register(aiohttp.ClientSession, manage_clientsession)
app = aiohttp.web.Application()
app['d'] = d
app.on_shutdown.append(teardown_deps)
return app
async def teardown_deps(app):
await app['d'].async_teardown()Next, use the ClientSession instance somewhere in your app:
async def somewhere(app):
session = await app['d'].aget(aiohttp.ClientSession)
async with session.get('https://python.org') as resp:
...The first call to aget will setup the ClientSession instance.
Subsequent calls will return the same instance.
An often occurring pattern is injecting dependencies into dependencies:
class TwitterClient:
def __init__(self,config,session):
self.config = config
self.session = session
async def setup_access_token(self):
url = self.config.TWITTER_TOKEN_URL
async with self.session.post(url, ...) as resp:
...
@staticmethod
@asynccontextmanager
async def manage_me(d):
yield TwitterClient(d['config'], await d.aget(aiohttp.ClientSession))At the app configuration, pass the dependency provider:
d.register(TwitterClient,TwitterClient.manage_me,d)Registering simple dependencies is possible without a context manager.
d.register('config',lambda: read_config_file())
