feat: Raise NotImplementedError for event interfaces lacking DISPIDs.

Replace `assert` in `CreateEventReceiver` with an explicit check for `dispid`,
raising `NotImplementedError` with a message when DISPIDs are missing.

Author: junkmd

comtypes/client/_events.py

@@ -262,7 +262,15 @@ def _get_method_finder_(self, itf: type[IUnknown]) -> _MethodFinder:
             # Can dispid be at a different index? Should check code generator...
             # ...but hand-written code should also work...
             dispid = m.idlflags[0]
-            assert isinstance(dispid, comtypes.dispid)
+            if not isinstance(dispid, comtypes.dispid):
+                # The interface is a subclass of `IDispatch` but its methods do not
+                # have DISPIDs, indicating it's not an interface suitable for event
+                # handling.
+                raise NotImplementedError(
+                    "Event receiver creation requires event methods to have DISPIDs "
+                    f"for dispatching, but '{interface.__name__}' ({interface._iid_}) "
+                    "lacks them, even though it inherits from 'IDispatch'."
+                )
             impl = finder.get_impl(interface, m.name, m.paramflags, m.idlflags)
             # XXX Wouldn't work for 'propget', 'propput', 'propputref'
             # methods - are they allowed on event interfaces?

comtypes/test/test_eventinterface.py

@@ -146,10 +146,7 @@ def test(self):
         # `DFileSystemImageEvents`. Although it inherits from `IDispatch`,
         # it is a custom interface (`TKIND_INTERFACE`), not a dual or pure
         # dispatch interface (`TKIND_DISPATCH`).
-        # Its methods are v-table bound, and the interface definition
-        # that comtypes generates from the type info lacks the `dispid`
-        # attributes that `GetEvents` requires.
-        with self.assertRaises(AssertionError):
+        with self.assertRaises(NotImplementedError):
             GetEvents(self.image, sink)