Basic support for issubclass() on old style classes

src/runtime/builtin_modules/builtins.cpp

@@ -340,13 +340,21 @@ Box* isinstance_func(Box* obj, Box* cls) {
 }
 
 Box* issubclass_func(Box* child, Box* parent) {
-    if (parent->cls == classobj_cls) {
-        Py_FatalError("don't handle issubclass for old style classes yet");
+    if (child->cls != type_cls && child->cls != classobj_cls)
+        raiseExcHelper(TypeError, "issubclass() arg 1 must be a class");
+
+    RELEASE_ASSERT(parent->cls != tuple_cls, "unsupported");
+
+    if (child->cls == classobj_cls) {
+        if (parent->cls != classobj_cls)
+            return False;
+
+        return boxBool(classobjIssubclass(static_cast<BoxedClassobj*>(child), static_cast<BoxedClassobj*>(parent)));
     }
 
-    RELEASE_ASSERT(child->cls == type_cls, "");
-    // TODO parent can also be a tuple of classes
-    RELEASE_ASSERT(parent->cls == type_cls, "");
+    assert(child->cls == type_cls);
+    if (parent->cls != type_cls)
+        return False;
 
     return boxBool(isSubclass(static_cast<BoxedClass*>(child), static_cast<BoxedClass*>(parent)));
 }

src/runtime/classobj.cpp

@@ -25,19 +25,19 @@ namespace pyston {
 
 BoxedClass* classobj_cls, *instance_cls;
 
-bool classIssubclass(BoxedClassobj* child, BoxedClassobj* parent) {
+bool classobjIssubclass(BoxedClassobj* child, BoxedClassobj* parent) {
     if (child == parent)
         return true;
 
     for (auto e : child->bases->elts) {
-        if (e->cls == classobj_cls && classIssubclass(static_cast<BoxedClassobj*>(e), parent))
+        if (e->cls == classobj_cls && classobjIssubclass(static_cast<BoxedClassobj*>(e), parent))
             return true;
     }
     return false;
 }
 
 bool instanceIsinstance(BoxedInstance* obj, BoxedClassobj* cls) {
-    return classIssubclass(obj->inst_cls, cls);
+    return classobjIssubclass(obj->inst_cls, cls);
 }
 
 static Box* classLookup(BoxedClassobj* cls, const std::string& attr) {

src/runtime/classobj.h

@@ -27,6 +27,7 @@ class BoxedInstance;
 extern BoxedClass* classobj_cls, *instance_cls;
 
 bool instanceIsinstance(BoxedInstance* obj, BoxedClassobj* cls);
+bool classobjIssubclass(BoxedClassobj* child, BoxedClassobj* parent);
 
 class BoxedClassobj : public Box {
 public:

test/tests/oldstyle_classes.py

@@ -102,3 +102,12 @@ print isinstance(D(), C)
 
 print str(f)[:26]
 print repr(f)[:26]
+
+
+class OldStyleClass:
+    pass
+
+print issubclass(OldStyleClass, object)
+
+print isinstance(OldStyleClass(), OldStyleClass)
+print issubclass(OldStyleClass, OldStyleClass)