The code has been refactored

fastapi/dependencies/protocols.py

@@ -0,0 +1,11 @@
+from typing import Any, Tuple
+
+from typing_extensions import Protocol
+
+
+class GenericTypeProtocol(Protocol):
+    class OriginTypeProtocol(Protocol):
+        __parameters__: Tuple[Any]
+
+    __origin__: OriginTypeProtocol
+    __args__: Tuple[Any]

fastapi/dependencies/stubs.py

@@ -1,9 +0,0 @@
-from typing import Any, Tuple
-
-
-class GenericTypeStub:
-    class OriginTypeStub:
-        __parameters__: Tuple[Any]
-
-    __origin__: OriginTypeStub
-    __args__: Tuple[Any]

fastapi/dependencies/utils.py

@@ -26,7 +26,7 @@ from fastapi.concurrency import (
     contextmanager_in_threadpool,
 )
 from fastapi.dependencies.models import Dependant, SecurityRequirement
-from fastapi.dependencies.stubs import GenericTypeStub
+from fastapi.dependencies.protocols import GenericTypeProtocol
 from fastapi.logger import logger
 from fastapi.security.base import SecurityBase
 from fastapi.security.oauth2 import OAuth2, SecurityScopes
@@ -264,14 +264,12 @@ def substitute_generic_type(annotation: Any, typevars: Dict[str, Any]) -> Any:
 def get_typed_signature(call: Callable[..., Any]) -> inspect.Signature:
     typevars = None
     if is_generic_type(call):
-        generic: GenericTypeStub = cast(GenericTypeStub, call)
+        generic: GenericTypeProtocol = cast(GenericTypeProtocol, call)
+        origin: Any = generic.__origin__
         typevars = {
             typevar.__name__: value
-            for typevar, value in zip(
+            for typevar, value in zip(origin.__parameters__, generic.__args__)
-                generic.__origin__.__parameters__, generic.__args__
-            )
         }
-        origin: Any = generic.__origin__
         call = origin.__init__
 
     signature = inspect.signature(call)