Improve type hints and tests for IClassFactory.CreateInstance and CoGetClassObject.

comtypes/_post_coinit/misc.py

@@ -160,8 +160,12 @@ def CoGetClassObject(
     ) -> _T_IUnknown: ...
 
 
-def CoGetClassObject(clsid, clsctx=None, pServerInfo=None, interface=None):
-    # type: (GUID, Optional[int], Optional[COSERVERINFO], Optional[Type[IUnknown]]) -> IUnknown
+def CoGetClassObject(
+    clsid: GUID,
+    clsctx: Optional[int] = None,
+    pServerInfo: "Optional[COSERVERINFO]" = None,
+    interface: Optional[type[IUnknown]] = None,
+) -> IUnknown:
     if clsctx is None:
         clsctx = CLSCTX_SERVER
     if interface is None:

comtypes/server/__init__.py

@@ -1,6 +1,6 @@
 import ctypes
 from ctypes import HRESULT, POINTER, byref
-from typing import TYPE_CHECKING, Any, Optional
+from typing import TYPE_CHECKING, Any, Literal, Optional, TypeVar, overload
 
 import comtypes
 import comtypes.client
@@ -15,6 +15,9 @@
     from comtypes import hints  # type: ignore
 
 
+_T_IUnknown = TypeVar("_T_IUnknown", bound=IUnknown)
+
+
 ################################################################
 # Interfaces
 class IClassFactory(IUnknown):
@@ -28,9 +31,23 @@ class IClassFactory(IUnknown):
         STDMETHOD(HRESULT, "LockServer", [ctypes.c_int]),
     ]
 
+    @overload
+    def CreateInstance(
+        self,
+        punkouter: Optional["_Pointer[IUnknown]"] = None,
+        interface: type[_T_IUnknown] = IUnknown,
+        dynamic: Literal[False] = False,
+    ) -> _T_IUnknown: ...
+    @overload
+    def CreateInstance(
+        self,
+        punkouter: Optional["_Pointer[IUnknown]"] = None,
+        interface: None = None,
+        dynamic: Literal[True] = True,
+    ) -> Any: ...
     def CreateInstance(
         self,
-        punkouter: Optional[type["_Pointer[IUnknown]"]] = None,
+        punkouter: Optional["_Pointer[IUnknown]"] = None,
         interface: Optional[type[IUnknown]] = None,
         dynamic: bool = False,
     ) -> Any:

comtypes/test/test_classfactory.py

@@ -0,0 +1,43 @@
+import unittest as ut
+
+from comtypes import GUID, CoGetClassObject, IUnknown, shelllink
+from comtypes.server import IClassFactory
+
+CLSID_ShellLink = GUID("{00021401-0000-0000-C000-000000000046}")
+
+REGDB_E_CLASSNOTREG = -2147221164  # 0x80040154
+
+
+class Test_CreateInstance(ut.TestCase):
+    def test_returns_specified_interface_type_instance(self):
+        class_factory = CoGetClassObject(CLSID_ShellLink)
+        self.assertIsInstance(class_factory, IClassFactory)
+        shlnk = class_factory.CreateInstance(interface=shelllink.IShellLinkW)
+        self.assertIsInstance(shlnk, shelllink.IShellLinkW)
+        shlnk.SetDescription("sample")
+        self.assertEqual(shlnk.GetDescription(), "sample")
+
+    def test_returns_iunknown_type_instance(self):
+        class_factory = CoGetClassObject(CLSID_ShellLink)
+        self.assertIsInstance(class_factory, IClassFactory)
+        punk = class_factory.CreateInstance()
+        self.assertIsInstance(punk, IUnknown)
+        self.assertNotIsInstance(punk, shelllink.IShellLinkW)
+        shlnk = punk.QueryInterface(shelllink.IShellLinkW)
+        shlnk.SetDescription("sample")
+        self.assertEqual(shlnk.GetDescription(), "sample")
+
+    def test_raises_valueerror_if_takes_dynamic_true_and_interface_explicitly(self):
+        class_factory = CoGetClassObject(CLSID_ShellLink)
+        self.assertIsInstance(class_factory, IClassFactory)
+        with self.assertRaises(ValueError):
+            class_factory.CreateInstance(  # type: ignore
+                interface=shelllink.IShellLinkW,
+                dynamic=True,  # type: ignore
+            )
+
+    def test_raises_class_not_reg_error_if_non_existent_clsid(self):
+        # calling `CoGetClassObject` with a non-existent CLSID raises an `OSError`.
+        with self.assertRaises(OSError) as cm:
+            CoGetClassObject(GUID.create_new())
+        self.assertEqual(cm.exception.winerror, REGDB_E_CLASSNOTREG)