starlette/docs/applications.md

Starlette includes an application class Starlette that nicely ties together all of its other functionality.

from starlette.applications import Starlette
from starlette.responses import PlainTextResponse
from starlette.routing import Route, Mount, WebSocketRoute
from starlette.staticfiles import StaticFiles


def homepage(request):
    return PlainTextResponse('Hello, world!')

def user_me(request):
    username = "John Doe"
    return PlainTextResponse('Hello, %s!' % username)

def user(request):
    username = request.path_params['username']
    return PlainTextResponse('Hello, %s!' % username)

async def websocket_endpoint(websocket):
    await websocket.accept()
    await websocket.send_text('Hello, websocket!')
    await websocket.close()

def startup():
    print('Ready to go')


routes = [
    Route('/', homepage),
    Route('/user/me', user_me),
    Route('/user/{username}', user),
    WebSocketRoute('/ws', websocket_endpoint),
    Mount('/static', StaticFiles(directory="static")),
]

app = Starlette(debug=True, routes=routes, on_startup=[startup])

Instantiating the application

::: starlette.applications.Starlette :docstring:

Storing state on the app instance

You can store arbitrary extra state on the application instance, using the generic app.state attribute.

For example:

app.state.ADMIN_EMAIL = 'admin@example.org'

Accessing the app instance

Where a request is available (i.e. endpoints and middleware), the app is available on request.app.