Improve the error message when missing an annotation

Author: johnslavik

Lib/functools.py

@@ -1003,8 +1003,8 @@ def register(cls, func=None, _func_is_method=False):
             except KeyError:
                 raise TypeError(
                     f"Invalid first argument to `register()`: {func!r}. "
-                    f"Add missing type annotation to parameter {argname!r} "
-                    "of this function or use `@register(some_class)`."
+                    "Use either `@register(some_class)` or add a type "
+                    f"annotation to parameter {argname!r} of your callable."
                 ) from None
 
             if not _is_valid_dispatch_type(cls):

Lib/test/test_functools.py

@@ -3263,8 +3263,8 @@ def _(arg, extra: int):
             "<function TestSingleDispatch.test_invalid_registrations.<locals>._"
         )
         self.assertEndsWith(str(exc.exception),
-            "Add missing type annotation to parameter 'arg' "
-            "of this function or use `@register(some_class)`.")
+            "Use either `@register(some_class)` or add a type annotation "
+            f"to parameter 'arg' of your callable.")
 
         with self.assertRaises(TypeError) as exc:
             @i.register