Don't iterate over the MRO when only bases are needed

A5rocks · A5rocks · commit c85fe853dbe9 · 2021-12-10T09:02:44.000+09:00
diff --git a/mypy/semanal.py b/mypy/semanal.py
@@ -1196,14 +1196,13 @@ def analyze_class(self, defn: ClassDef) -> None:
 
     # should this be memoized in TypeInfo?
     def find_maximum_class_id(self, info: TypeInfo) -> int:
-        # top class?
-        if len(info.mro) in (0, 1):
-            return len(info.type_vars)
-        else:
+        if info.bases:
             return len(info.type_vars) + max(
-                self.find_maximum_class_id(cls)
-                for cls in info.mro[1:]
+                self.find_maximum_class_id(cls.type)
+                for cls in info.bases
             )
+        else:
+            return len(info.type_vars)
 
     def is_core_builtin_class(self, defn: ClassDef) -> bool:
         return self.cur_mod_id == 'builtins' and defn.name in CORE_BUILTIN_CLASSES
