list.extend returns None

src/runtime/list.cpp

@@ -783,6 +783,11 @@ Box* listIAdd(BoxedList* self, Box* _rhs) {
     return self;
 }
 
+Box* listExtend(BoxedList* self, Box* _rhs) {
+    listIAdd(self, _rhs);
+    return None;
+}
+
 Box* listAdd(BoxedList* self, Box* _rhs) {
     if (!PyList_Check(_rhs)) {
         return NotImplemented;
@@ -1344,7 +1349,7 @@ void setupList() {
                        new BoxedFunction(FunctionMetadata::create((void*)listPop, UNKNOWN, 2, false, false), { None }));
 
     list_cls->giveAttr("append", new BoxedFunction(FunctionMetadata::create((void*)listAppend, NONE, 2)));
-    list_cls->giveAttr("extend", new BoxedFunction(FunctionMetadata::create((void*)listIAdd, UNKNOWN, 2)));
+    list_cls->giveAttr("extend", new BoxedFunction(FunctionMetadata::create((void*)listExtend, NONE, 2)));
 
     list_cls->giveAttr("insert", new BoxedFunction(FunctionMetadata::create((void*)listInsert, NONE, 3)));
     list_cls->giveAttr("__mul__", new BoxedFunction(FunctionMetadata::create((void*)listMul, UNKNOWN, 2)));

test/tests/list.py

@@ -85,7 +85,7 @@ while l:
     del l[0]
 
 l = range(5)
-l.extend(range(5))
+print l.extend(range(5))
 print l
 
 # Repeating a list