final Ensured always, TypeError raised from metaclass

overrides/enforce.py

@@ -12,39 +12,45 @@ def __new__(mcls, name, bases, namespace, **kwargs):
 
         cls = super().__new__(mcls, name, bases, namespace, **kwargs)
         for name, value in namespace.items():
-            # Actually checking the direct parent should be enough,
-            # otherwise the error would have emerged during the parent class checking
-            if name.startswith("__"):
-                continue
-            value = mcls.handle_special_value(value)
-            is_override = getattr(value, "__override__", False)
-            for base in bases:
-                base_class_method = getattr(base, name, False)
-                if (
+            mcls._check_if_overrides_final_method(name, bases)
+            if not name.startswith("__"):
+                value = mcls._handle_special_value(value)
+                mcls._check_if_overrides_without_overrides_decorator(name, value, bases)
+        return cls
+
+    @staticmethod
+    def _check_if_overrides_without_overrides_decorator(name, value, bases):
+        is_override = getattr(value, "__override__", False)
+        for base in bases:
+            base_class_method = getattr(base, name, False)
+            if (
                     not base_class_method
                     or not callable(base_class_method)
                     or getattr(base_class_method, "__ignored__", False)
-                ):
-                    continue
-                assert (
-                    is_override
-                ), "Method %s overrides but does not have @overrides decorator" % (name)
-                # `__finalized__` is added by `@final` decorator
-                assert not getattr(base_class_method, "__finalized__", False), (
-                    "Method %s is finalized in %s, it cannot be overridden"
-                    % (base_class_method, base,)
-                )
-        return cls
+            ):
+                continue
+            if not is_override:
+                raise TypeError(f"Method {name} overrides but does not have @overrides decorator")
+    @staticmethod
+    def _check_if_overrides_final_method(name, bases):
+        for base in bases:
+            base_class_method = getattr(base, name, False)
+            # `__finalized__` is added by `@final` decorator
+            if getattr(base_class_method, "__finalized__", False):
+                raise TypeError(
+                    f"Method {base_class_method} is finalized in {base}, it cannot be overridden"
+            )
 
     @staticmethod
-    def handle_special_value(value):
+    def _handle_special_value(value):
         if isinstance(value, classmethod) or isinstance(value, staticmethod):
             value = value.__get__(None, dict)
         elif isinstance(value, property):
             value = value.fget
         return value
 
 
+
 class EnforceOverrides(metaclass=EnforceOverridesMeta):
     "Use this as the parent class for your custom classes"
     pass

tests/test_enforce__py38.py

@@ -12,6 +12,11 @@ class Enforcing(EnforceOverrides):
     def finality(self):
         return "final"
 
+
+    @final
+    def __and__(self, other):
+        return True
+
     def nonfinal1(self, param: int) -> str:
         return "super1"
 
@@ -47,26 +52,23 @@ def nonfinal1(self, param: int) -> str:
         self.assertEqual(sc.classVariableIsOk, "OK!")
 
     def test_enforcing_when_finality_broken(self):
-        try:
-
+        with self.assertRaises(TypeError):
             class BrokesFinality(Enforcing):
                 def finality(self):
                     return "NEVER HERE"
 
-            raise RuntimeError("Should not go here")
-        except AssertionError:
-            pass
+    def test_trying_to_override_final_magic_method(self):
+        with self.assertRaises(TypeError):
+            class FinalMagicOverrides(Enforcing):
+                def __and__(self, other):
+                    return False
 
     def test_enforcing_when_none_explicit_override(self):
-        try:
-
+        with self.assertRaises(TypeError):
             class Overrider(Enforcing):
                 def nonfinal2(self):
                     return "NEVER HERE EITHER"
 
-            raise RuntimeError("Should not go here")
-        except AssertionError:
-            pass
 
     def test_enforcing_when_property_overriden(self):
         class PropertyOverrider(Enforcing):
@@ -116,7 +118,7 @@ class MetaClassMethodOverrider(Enforcing):
             def register(self):
                 pass
 
-        with self.assertRaises(AssertionError):
+        with self.assertRaises(TypeError):
 
             class SubClass(MetaClassMethodOverrider):
                 def register(self):