Starlette includes an application class Starlette that nicely ties together all of
+its other functionality.
from contextlib import asynccontextmanager
+
+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()
+
+@asynccontextmanager
+async def lifespan(app):
+ print('Startup')
+ yield
+ print('Shutdown')
+
+
+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, lifespan=lifespan)
+Starlette(debug: bool = False, routes: Sequence[BaseRoute] | None = None, middleware: Sequence[Middleware] | None = None, exception_handlers: Mapping[Any, ExceptionHandler] | None = None, on_startup: Sequence[Callable[[], Any]] | None = None, on_shutdown: Sequence[Callable[[], Any]] | None = None, lifespan: Lifespan[AppType] | None = None)
+Creates an Starlette application.
+ + + +Parameters:
+debug
+ (bool, default:
+ False
+)
+ –
+ Boolean indicating if debug tracebacks should be returned on errors.
+routes
+ (Sequence[BaseRoute] | None, default:
+ None
+)
+ –
+ A list of routes to serve incoming HTTP and WebSocket requests.
+middleware
+ (Sequence[Middleware] | None, default:
+ None
+)
+ –
+ A list of middleware to run for every request. A starlette
+application will always automatically include two middleware classes.
+ServerErrorMiddleware is added as the very outermost middleware, to handle
+any uncaught errors occurring anywhere in the entire stack.
+ExceptionMiddleware is added as the very innermost middleware, to deal
+with handled exception cases occurring in the routing or endpoints.
exception_handlers
+ (Mapping[Any, ExceptionHandler] | None, default:
+ None
+)
+ –
+ A mapping of either integer status codes,
+or exception class types onto callables which handle the exceptions.
+Exception handler callables should be of the form
+handler(request, exc) -> response and may be either standard functions, or
+async functions.
on_startup
+ (Sequence[Callable[[], Any]] | None, default:
+ None
+)
+ –
+ A list of callables to run on application startup. +Startup handler callables do not take any arguments, and may be either +standard functions, or async functions.
+on_shutdown
+ (Sequence[Callable[[], Any]] | None, default:
+ None
+)
+ –
+ A list of callables to run on application shutdown. +Shutdown handler callables do not take any arguments, and may be either +standard functions, or async functions.
+lifespan
+ (Lifespan[AppType] | None, default:
+ None
+)
+ –
+ A lifespan context function, which can be used to perform
+startup and shutdown tasks. This is a newer style that replaces the
+on_startup and on_shutdown handlers. Use one or the other, not both.
starlette/applications.py30 +31 +32 +33 +34 +35 +36 +37 +38 +39 +40 +41 +42 +43 +44 +45 +46 +47 +48 +49 +50 +51 +52 +53 +54 +55 +56 +57 +58 +59 +60 +61 +62 +63 +64 +65 +66 +67 +68 +69 +70 +71 +72 +73 +74 +75 +76 +77 | |
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'
+Where a request is available (i.e. endpoints and middleware), the app is available on request.app.