refactor: use singleton decorator to extract Litestar

main.py

@@ -1,7 +1,6 @@
 from granian import Granian
 from granian.constants import Interfaces
 
-from server import App
 from server.config import Config
 
 
@@ -12,7 +11,7 @@ def main():
     programmatically run the server with Granian
     """
     granian = Granian(
-        f'{App.__module__}:{App.__name__}',
+        'server:app',
         '0.0.0.0',
         Config.server_port,
         Interfaces.ASGI,

server/__init__.py

@@ -2,12 +2,12 @@
 from litestar.openapi import OpenAPIConfig
 from litestar.openapi.spec import Server
 from litestar.status_codes import HTTP_500_INTERNAL_SERVER_ERROR
-from litestar.types import LifeSpanReceive, LifeSpanScope, LifeSpanSend, Receive, Scope, Send
 from picologging import getLogger
 
 from server.api import v1
 from server.config import Config
 from server.lifespans import load_model
+from server.singleton import singleton
 
 
 def exception_handler(_, exception: Exception) -> Response[dict[str, str]]:
@@ -29,30 +29,11 @@ def exception_handler(_, exception: Exception) -> Response[dict[str, str]]:
     )
 
 
-class App:
-    """
-    Summary
-    -------
-    the ASGI application wrapper
-
-    Parameters
-    ----------
-    scope (Scope) : the ASGI scope
-    receive (Receive) : the ASGI receive channel
-    send (Send) : the ASGI send channel
-    """
-
-    asgi = Litestar(
+@singleton
+def app() -> Litestar:
+    return Litestar(
         openapi_config=OpenAPIConfig(title='CapGen', version='1.0.0', servers=[Server(url=Config.server_root_path)]),
         exception_handlers={HTTP_500_INTERNAL_SERVER_ERROR: exception_handler},
         route_handlers=[v1],
         lifespan=[load_model],
     )
-
-    async def __new__(  # pylint: disable=invalid-overridden-method
-        cls,
-        scope: Scope | LifeSpanScope,
-        receive: Receive | LifeSpanReceive,
-        send: Send | LifeSpanSend,
-    ):
-        await cls.asgi(scope, receive, send)

server/config.py

@@ -2,24 +2,9 @@
 
 from pydantic_settings import BaseSettings
 
-T = TypeVar('T')
-
-
-def singleton(cls: type[T]) -> T:
-    """
-    Summary
-    -------
-    a decorator to make a class a singleton
+from server.singleton import singleton
 
-    Parameters
-    ----------
-    cls (type[T]) : the class to make a singleton
-
-    Returns
-    -------
-    instance (T) : the singleton instance
-    """
-    return cls()
+T = TypeVar('T')
 
 
 @singleton

server/singleton.py

@@ -0,0 +1,18 @@
+from typing import Callable
+
+
+def singleton[T](callable_object: Callable[[], T]) -> T:
+    """
+    Summary
+    -------
+    a decorator to transform a callable/class to a singleton
+
+    Parameters
+    ----------
+    callable_object (Callable[[], T]) : the callable to transform
+
+    Returns
+    -------
+    instance (T) : the singleton
+    """
+    return callable_object()

tests/conftest.py

@@ -6,10 +6,10 @@
 from litestar.testing import AsyncTestClient
 from pytest import fixture
 
-from server import App
+from server import app
 
 
 @fixture(scope='function')
 async def client() -> AsyncIterator[AsyncTestClient[Litestar]]:
-    async with AsyncTestClient(app=App.asgi) as client:
+    async with AsyncTestClient(app=app) as client:
         yield client