Fix typing of Lifespan to allow subclasses of Starlette

starlette/applications.py

@@ -43,7 +43,7 @@ class Starlette:
     """
 
     def __init__(
-        self,
+        self: "AppType",
         debug: bool = False,
         routes: typing.Optional[typing.Sequence[BaseRoute]] = None,
         middleware: typing.Optional[typing.Sequence[Middleware]] = None,
@@ -58,7 +58,7 @@ def __init__(
         ] = None,
         on_startup: typing.Optional[typing.Sequence[typing.Callable]] = None,
         on_shutdown: typing.Optional[typing.Sequence[typing.Callable]] = None,
-        lifespan: typing.Optional[Lifespan] = None,
+        lifespan: typing.Optional[Lifespan["AppType"]] = None,
     ) -> None:
         # The lifespan context function is a newer style that replaces
         # on_startup / on_shutdown handlers. Use one or the other, not both.
@@ -257,3 +257,6 @@ def decorator(func: typing.Callable) -> typing.Callable:
             return func
 
         return decorator
+
+
+AppType = typing.TypeVar("AppType", bound=Starlette)

starlette/types.py

@@ -1,7 +1,6 @@
 import typing
 
-if typing.TYPE_CHECKING:
-    from starlette.applications import Starlette
+T = typing.TypeVar("T")
 
 Scope = typing.MutableMapping[str, typing.Any]
 Message = typing.MutableMapping[str, typing.Any]
@@ -11,8 +10,8 @@
 
 ASGIApp = typing.Callable[[Scope, Receive, Send], typing.Awaitable[None]]
 
-StatelessLifespan = typing.Callable[["Starlette"], typing.AsyncContextManager[None]]
+StatelessLifespan = typing.Callable[[T], typing.AsyncContextManager[None]]
 StatefulLifespan = typing.Callable[
-    ["Starlette"], typing.AsyncContextManager[typing.Mapping[str, typing.Any]]
+    [T], typing.AsyncContextManager[typing.Mapping[str, typing.Any]]
 ]
-Lifespan = typing.Union[StatelessLifespan, StatefulLifespan]
+Lifespan = typing.Union[StatelessLifespan[T], StatefulLifespan[T]]

tests/test_applications.py

@@ -1,6 +1,6 @@
 import os
 from contextlib import asynccontextmanager
-from typing import Any, Callable
+from typing import Any, AsyncIterator, Callable
 
 import anyio
 import httpx
@@ -534,3 +534,14 @@ def get_app() -> ASGIApp:
     test_client_factory(app).get("/foo")
 
     assert SimpleInitializableMiddleware.counter == 2
+
+
+def test_lifespan_typing():
+    class App(Starlette):
+        pass
+
+    @asynccontextmanager
+    async def lifespan(app: App) -> AsyncIterator[None]:  # pragma: no cover
+        yield
+
+    App(lifespan=lifespan)