Allow subclassing of properties

src/runtime/descr.cpp

@@ -91,9 +91,7 @@ static Box* propertyDel(Box* self, Box* obj) {
 }
 
 static Box* property_copy(BoxedProperty* old, Box* get, Box* set, Box* del) {
-    // In CPython, I think this can take a subclass of property, and will call the subclass's
-    // constructor... for now just enforce that it's a property object and inline the constructor:
-    RELEASE_ASSERT(old->cls == property_cls, "");
+    RELEASE_ASSERT(isSubclass(old->cls, property_cls), "");
 
     if (!get)
         get = old->prop_get;
@@ -102,7 +100,10 @@ static Box* property_copy(BoxedProperty* old, Box* get, Box* set, Box* del) {
     if (!del)
         del = old->prop_del;
 
-    return new BoxedProperty(get, set, del, old->prop_doc);
+    // Optimization for the case when the old propery is not subclassed
+    if (old->cls == property_cls)
+        return new BoxedProperty(get, set, del, old->prop_doc);
+    return runtimeCall(old->cls, ArgPassSpec(4), get, set, del, &old->prop_doc, NULL);
 }
 
 static Box* propertyGetter(Box* self, Box* obj) {

test/tests/property.py

@@ -63,3 +63,22 @@ try:
 except AttributeError, e:
     print e
 c.x = 1
+
+class MyProperty(property):
+    pass
+
+class C(object):
+    v = "empty"
+    @MyProperty
+    def p(self):
+        print "get"
+        return self.v
+
+    @p.setter
+    def p(self, value):
+        print "set"
+        self.v = "it " + value
+
+c = C()
+c.p = "worked"
+print c.p