Use Py_VISIT in all tp_traverse methods, instead of traversing manually or

using a custom, nearly-identical macro. This probably changes how some of
these functions are compiled, which may result in fractionally slower (or
faster) execution. Considering the nature of traversal, visiting much of the
address space in unpredictable patterns, I'd argue the code readability and
maintainability is well worth it ;P

Modules/_csv.c

@@ -48,7 +48,16 @@ module instead.
 		}						\
 	} while (0)
 #endif
-
+#ifndef Py_VISIT
+#define Py_VISIT(op)							\
+        do { 								\
+                if (op) {						\
+                        int vret = visit((PyObject *)(op), arg);	\
+                        if (vret)					\
+                                return vret;				\
+                }							\
+        } while (0)
+#endif
 
 /* end 2.2 compatibility macros */
 
@@ -825,16 +834,9 @@ Reader_dealloc(ReaderObj *self)
 static int
 Reader_traverse(ReaderObj *self, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(self->dialect);
-#define VISIT(SLOT) \
+	Py_VISIT(self->input_iter);
-	if (SLOT) { \
+	Py_VISIT(self->fields);
-		err = visit((PyObject *)(SLOT), arg); \
-		if (err) \
-			return err; \
-	}
-	VISIT(self->dialect);
-	VISIT(self->input_iter);
-	VISIT(self->fields);
 	return 0;
 }
 
@@ -1255,15 +1257,8 @@ Writer_dealloc(WriterObj *self)
 static int
 Writer_traverse(WriterObj *self, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(self->dialect);
-#define VISIT(SLOT) \
+	Py_VISIT(self->writeline);
-	if (SLOT) { \
-		err = visit((PyObject *)(SLOT), arg); \
-		if (err) \
-			return err; \
-	}
-	VISIT(self->dialect);
-	VISIT(self->writeline);
 	return 0;
 }
 

Modules/arraymodule.c

@@ -2061,8 +2061,7 @@ arrayiter_dealloc(arrayiterobject *it)
 static int
 arrayiter_traverse(arrayiterobject *it, visitproc visit, void *arg)
 {
-	if (it->ao != NULL)
+	Py_VISIT(it->ao);
-		return visit((PyObject *)(it->ao), arg);
 	return 0;
 }
 

Modules/cPickle.c

@@ -2909,22 +2909,14 @@ Pickler_dealloc(Picklerobject *self)
 static int
 Pickler_traverse(Picklerobject *self, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(self->write);
-#define VISIT(SLOT) \
+	Py_VISIT(self->memo);
-	if (SLOT) { \
+	Py_VISIT(self->fast_memo);
-		err = visit((PyObject *)(SLOT), arg); \
+	Py_VISIT(self->arg);
-		if (err) \
+	Py_VISIT(self->file);
-			return err; \
+	Py_VISIT(self->pers_func);
-	}
+	Py_VISIT(self->inst_pers_func);
-	VISIT(self->write);
+	Py_VISIT(self->dispatch_table);
-	VISIT(self->memo);
-	VISIT(self->fast_memo);
-	VISIT(self->arg);
-	VISIT(self->file);
-	VISIT(self->pers_func);
-	VISIT(self->inst_pers_func);
-	VISIT(self->dispatch_table);
-#undef VISIT
 	return 0;
 }
 
@@ -5258,24 +5250,15 @@ Unpickler_dealloc(Unpicklerobject *self)
 static int
 Unpickler_traverse(Unpicklerobject *self, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(self->readline);
-
+	Py_VISIT(self->read);
-#define VISIT(SLOT) \
+	Py_VISIT(self->file);
-	if (SLOT) { \
+	Py_VISIT(self->memo);
-		err = visit((PyObject *)(SLOT), arg); \
+	Py_VISIT(self->stack);
-		if (err) \
+	Py_VISIT(self->pers_func);
-			return err; \
+	Py_VISIT(self->arg);
-	}
+	Py_VISIT(self->last_string);
-	VISIT(self->readline);
+	Py_VISIT(self->find_class);
-	VISIT(self->read);
-	VISIT(self->file);
-	VISIT(self->memo);
-	VISIT(self->stack);
-	VISIT(self->pers_func);
-	VISIT(self->arg);
-	VISIT(self->last_string);
-	VISIT(self->find_class);
-#undef VISIT
 	return 0;
 }
 

Modules/operator.c

@@ -358,8 +358,7 @@ itemgetter_dealloc(itemgetterobject *ig)
 static int
 itemgetter_traverse(itemgetterobject *ig, visitproc visit, void *arg)
 {
-	if (ig->item)
+	Py_VISIT(ig->item);
-		return visit(ig->item, arg);
 	return 0;
 }
 
@@ -497,8 +496,7 @@ attrgetter_dealloc(attrgetterobject *ag)
 static int
 attrgetter_traverse(attrgetterobject *ag, visitproc visit, void *arg)
 {
-	if (ag->attr)
+	Py_VISIT(ag->attr);
-		return visit(ag->attr, arg);
 	return 0;
 }
 

Modules/pyexpat.c

@@ -1655,13 +1655,8 @@ static int
 xmlparse_traverse(xmlparseobject *op, visitproc visit, void *arg)
 {
     int i, err;
-    for (i = 0; handler_info[i].name != NULL; i++) {
+    for (i = 0; handler_info[i].name != NULL; i++)
-        if (!op->handlers[i])
+        Py_VISIT(op->handlers[i]);
-            continue;
-        err = visit(op->handlers[i], arg);
-        if (err)
-            return err;
-    }
     return 0;
 }
 

Modules/zipimport.c

@@ -170,13 +170,7 @@ static int
 zipimporter_traverse(PyObject *obj, visitproc visit, void *arg)
 {
 	ZipImporter *self = (ZipImporter *)obj;
-	int err;
+	Py_VISIT(self->files);
-
-	if (self->files != NULL) {
-		err = visit(self->files, arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 

Objects/cellobject.c

@@ -73,8 +73,7 @@ cell_repr(PyCellObject *op)
 static int
 cell_traverse(PyCellObject *op, visitproc visit, void *arg)
 {
-	if (op->ob_ref)
+	Py_VISIT(op->ob_ref);
-		return visit(op->ob_ref, arg);
 	return 0;
 }
 

Objects/classobject.c

@@ -404,37 +404,12 @@ class_str(PyClassObject *op)
 static int
 class_traverse(PyClassObject *o, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(o->cl_bases);
-	if (o->cl_bases) {
+	Py_VISIT(o->cl_dict);
-		err = visit(o->cl_bases, arg);
+	Py_VISIT(o->cl_name);
-		if (err)
+	Py_VISIT(o->cl_getattr);
-			return err;
+	Py_VISIT(o->cl_setattr);
-	}
+	Py_VISIT(o->cl_delattr);
-	if (o->cl_dict) {
-		err = visit(o->cl_dict, arg);
-		if (err)
-			return err;
-	}
-	if (o->cl_name) {
-		err = visit(o->cl_name, arg);
-		if (err)
-			return err;
-	}
-	if (o->cl_getattr) {
-		err = visit(o->cl_getattr, arg);
-		if (err)
-			return err;
-	}
-	if (o->cl_setattr) {
-		err = visit(o->cl_setattr, arg);
-		if (err)
-			return err;
-	}
-	if (o->cl_delattr) {
-		err = visit(o->cl_delattr, arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 
@@ -979,17 +954,8 @@ instance_hash(PyInstanceObject *inst)
 static int
 instance_traverse(PyInstanceObject *o, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(o->in_class);
-	if (o->in_class) {
+	Py_VISIT(o->in_dict);
-		err = visit((PyObject *)(o->in_class), arg);
-		if (err)
-			return err;
-	}
-	if (o->in_dict) {
-		err = visit(o->in_dict, arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 
@@ -2348,22 +2314,9 @@ instancemethod_hash(PyMethodObject *a)
 static int
 instancemethod_traverse(PyMethodObject *im, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(im->im_func);
-	if (im->im_func) {
+	Py_VISIT(im->im_self);
-		err = visit(im->im_func, arg);
+	Py_VISIT(im->im_class);
-		if (err)
-			return err;
-	}
-	if (im->im_self) {
-		err = visit(im->im_self, arg);
-		if (err)
-			return err;
-	}
-	if (im->im_class) {
-		err = visit(im->im_class, arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 

Objects/descrobject.c

@@ -377,13 +377,7 @@ static int
 descr_traverse(PyObject *self, visitproc visit, void *arg)
 {
 	PyDescrObject *descr = (PyDescrObject *)self;
-	int err;
+	Py_VISIT(descr->d_type);
-
-	if (descr->d_type) {
-		err = visit((PyObject *)(descr->d_type), arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 
@@ -814,13 +808,7 @@ static int
 proxy_traverse(PyObject *self, visitproc visit, void *arg)
 {
 	proxyobject *pp = (proxyobject *)self;
-	int err;
+	Py_VISIT(pp->dict);
-
-	if (pp->dict) {
-		err = visit(pp->dict, arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 
@@ -999,18 +987,8 @@ static int
 wrapper_traverse(PyObject *self, visitproc visit, void *arg)
 {
 	wrapperobject *wp = (wrapperobject *)self;
-	int err;
+	Py_VISIT(wp->descr);
-
+	Py_VISIT(wp->self);
-	if (wp->descr) {
-		err = visit((PyObject *)(wp->descr), arg);
-		if (err)
-			return err;
-	}
-	if (wp->self) {
-		err = visit(wp->self, arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 
@@ -1237,20 +1215,10 @@ static int
 property_traverse(PyObject *self, visitproc visit, void *arg)
 {
 	propertyobject *pp = (propertyobject *)self;
-	int err;
+	Py_VISIT(pp->prop_get);
-
+	Py_VISIT(pp->prop_set);
-#define VISIT(SLOT) \
+	Py_VISIT(pp->prop_del);
-	if (pp->SLOT) { \
+	Py_VISIT(pp->prop_doc);
-		err = visit((PyObject *)(pp->SLOT), arg); \
-		if (err) \
-			return err; \
-	}
-
-	VISIT(prop_get);
-	VISIT(prop_set);
-	VISIT(prop_del);
-	VISIT(prop_doc);
-
 	return 0;
 }
 

Objects/dictobject.c

@@ -1732,17 +1732,12 @@ static int
 dict_traverse(PyObject *op, visitproc visit, void *arg)
 {
 	Py_ssize_t i = 0;
-	int err;
 	PyObject *pk;
 	PyObject *pv;
 
 	while (PyDict_Next(op, &i, &pk, &pv)) {
-		err = visit(pk, arg);
+		Py_VISIT(pk);
-		if (err)
+		Py_VISIT(pv);
-			return err;
-		err = visit(pv, arg);
-		if (err)
-			return err;
 	}
 	return 0;
 }

Objects/enumobject.c

@@ -49,18 +49,8 @@ enum_dealloc(enumobject *en)
 static int
 enum_traverse(enumobject *en, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(en->en_sit);
-
+	Py_VISIT(en->en_result);
-	if (en->en_sit) {
-		err = visit(en->en_sit, arg);
-		if (err)
-			return err;
-	}
-	if (en->en_result) {
-		err = visit(en->en_result, arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 
@@ -205,8 +195,7 @@ reversed_dealloc(reversedobject *ro)
 static int
 reversed_traverse(reversedobject *ro, visitproc visit, void *arg)
 {
-	if (ro->seq)
+	Py_VISIT(ro->seq);
-		return visit((PyObject *)(ro->seq), arg);
 	return 0;
 }
 

Objects/funcobject.c

@@ -466,47 +466,14 @@ func_repr(PyFunctionObject *op)
 static int
 func_traverse(PyFunctionObject *f, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(f->func_code);
-	if (f->func_code) {
+	Py_VISIT(f->func_globals);
-		err = visit(f->func_code, arg);
+	Py_VISIT(f->func_module);
-		if (err)
+	Py_VISIT(f->func_defaults);
-			return err;
+	Py_VISIT(f->func_doc);
-	}
+	Py_VISIT(f->func_name);
-	if (f->func_globals) {
+	Py_VISIT(f->func_dict);
-		err = visit(f->func_globals, arg);
+	Py_VISIT(f->func_closure);
-		if (err)
-			return err;
-	}
-	if (f->func_module) {
-		err = visit(f->func_module, arg);
-		if (err)
-			return err;
-	}
-	if (f->func_defaults) {
-		err = visit(f->func_defaults, arg);
-		if (err)
-			return err;
-	}
-	if (f->func_doc) {
-		err = visit(f->func_doc, arg);
-		if (err)
-			return err;
-	}
-	if (f->func_name) {
-		err = visit(f->func_name, arg);
-		if (err)
-			return err;
-	}
-	if (f->func_dict) {
-		err = visit(f->func_dict, arg);
-		if (err)
-			return err;
-	}
-	if (f->func_closure) {
-		err = visit(f->func_closure, arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 
@@ -647,9 +614,8 @@ cm_dealloc(classmethod *cm)
 static int
 cm_traverse(classmethod *cm, visitproc visit, void *arg)
 {
-	if (!cm->cm_callable)
+	Py_VISIT(cm->cm_callable);
-		return 0;
+	return 0;
-	return visit(cm->cm_callable, arg);
 }
 
 static int
@@ -806,9 +772,8 @@ sm_dealloc(staticmethod *sm)
 static int
 sm_traverse(staticmethod *sm, visitproc visit, void *arg)
 {
-	if (!sm->sm_callable)
+	Py_VISIT(sm->sm_callable);
-		return 0;
+	return 0;
-	return visit(sm->sm_callable, arg);
 }
 
 static int

Objects/iterobject.c

@@ -38,9 +38,8 @@ iter_dealloc(seqiterobject *it)
 static int
 iter_traverse(seqiterobject *it, visitproc visit, void *arg)
 {
-	if (it->it_seq == NULL)
+	Py_VISIT(it->it_seq);
-		return 0;
+	return 0;
-	return visit(it->it_seq, arg);
 }
 
 static PyObject *
@@ -162,11 +161,8 @@ calliter_dealloc(calliterobject *it)
 static int
 calliter_traverse(calliterobject *it, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(it->it_callable);
-	if (it->it_callable != NULL && (err = visit(it->it_callable, arg)))
+	Py_VISIT(it->it_sentinel);
-		return err;
-	if (it->it_sentinel != NULL && (err = visit(it->it_sentinel, arg)))
-		return err;
 	return 0;
 }
 

Objects/listobject.c

@@ -2276,14 +2276,8 @@ list_traverse(PyListObject *o, visitproc visit, void *arg)
 	Py_ssize_t i;
 	PyObject *x;
 
-	for (i = o->ob_size; --i >= 0; ) {
+	for (i = o->ob_size; --i >= 0; )
-		x = o->ob_item[i];
+		Py_VISIT(o->ob_item[i]);
-		if (x != NULL) {
-			int err = visit(x, arg);
-			if (err)
-				return err;
-		}
-	}
 	return 0;
 }
 
@@ -2779,9 +2773,8 @@ listiter_dealloc(listiterobject *it)
 static int
 listiter_traverse(listiterobject *it, visitproc visit, void *arg)
 {
-	if (it->it_seq == NULL)
+	Py_VISIT(it->it_seq);
-		return 0;
+	return 0;
-	return visit((PyObject *)it->it_seq, arg);
 }
 
 static PyObject *
@@ -2898,9 +2891,8 @@ listreviter_dealloc(listreviterobject *it)
 static int
 listreviter_traverse(listreviterobject *it, visitproc visit, void *arg)
 {
-	if (it->it_seq == NULL)
+	Py_VISIT(it->it_seq);
-		return 0;
+	return 0;
-	return visit((PyObject *)it->it_seq, arg);
 }
 
 static PyObject *

Objects/methodobject.c

@@ -149,17 +149,8 @@ meth_get__name__(PyCFunctionObject *m, void *closure)
 static int
 meth_traverse(PyCFunctionObject *m, visitproc visit, void *arg)
 {
-	int err;
+	Py_VISIT(m->m_self);
-	if (m->m_self != NULL) {
+	Py_VISIT(m->m_module);
-		err = visit(m->m_self, arg);
-		if (err)
-			return err;
-	}
-	if (m->m_module != NULL) {
-		err = visit(m->m_module, arg);
-		if (err)
-			return err;
-	}
 	return 0;
 }
 

Objects/moduleobject.c

@@ -204,8 +204,7 @@ module_repr(PyModuleObject *m)
 static int
 module_traverse(PyModuleObject *m, visitproc visit, void *arg)
 {
-	if (m->md_dict != NULL)
+	Py_VISIT(m->md_dict);
-		return visit(m->md_dict, arg);
 	return 0;
 }
 

Objects/tupleobject.c

@@ -438,16 +438,9 @@ static int
 tupletraverse(PyTupleObject *o, visitproc visit, void *arg)
 {
 	Py_ssize_t i;
-	PyObject *x;
 
-	for (i = o->ob_size; --i >= 0; ) {
+	for (i = o->ob_size; --i >= 0; )
-		x = o->ob_item[i];
+		Py_VISIT(o->ob_item[i]);
-		if (x != NULL) {
-			int err = visit(x, arg);
-			if (err)
-				return err;
-		}
-	}
 	return 0;
 }
 
@@ -802,9 +795,8 @@ tupleiter_dealloc(tupleiterobject *it)
 static int
 tupleiter_traverse(tupleiterobject *it, visitproc visit, void *arg)
 {
-	if (it->it_seq == NULL)
+	Py_VISIT(it->it_seq);
-		return 0;
+	return 0;
-	return visit((PyObject *)it->it_seq, arg);
 }
 
 static PyObject *

Objects/typeobject.c

@@ -525,21 +525,15 @@ subtype_traverse(PyObject *self, visitproc visit, void *arg)
 
 	if (type->tp_dictoffset != base->tp_dictoffset) {
 		PyObject **dictptr = _PyObject_GetDictPtr(self);
-		if (dictptr && *dictptr) {
+		if (dictptr && *dictptr)
-			int err = visit(*dictptr, arg);
+			Py_VISIT(*dictptr);
-			if (err)
-				return err;
-		}
 	}
 
-	if (type->tp_flags & Py_TPFLAGS_HEAPTYPE) {
+	if (type->tp_flags & Py_TPFLAGS_HEAPTYPE)
 		/* For a heaptype, the instances count as references
 		   to the type.  Traverse the type so the collector
 		   can find cycles involving this link. */
-		int err = visit((PyObject *)type, arg);
+		Py_VISIT(type);
-		if (err)
-			return err;
-	}
 
 	if (basetraverse)
 		return basetraverse(self, visit, arg);
@@ -2198,32 +2192,21 @@ PyDoc_STRVAR(type_doc,
 static int
 type_traverse(PyTypeObject *type, visitproc visit, void *arg)
 {
-	int err;
-
 	/* Because of type_is_gc(), the collector only calls this
 	   for heaptypes. */
 	assert(type->tp_flags & Py_TPFLAGS_HEAPTYPE);
 
-#define VISIT(SLOT) \
+	Py_VISIT(type->tp_dict);
-	if (SLOT) { \
+	Py_VISIT(type->tp_cache);
-		err = visit((PyObject *)(SLOT), arg); \
+	Py_VISIT(type->tp_mro);
-		if (err) \
+	Py_VISIT(type->tp_bases);
-			return err; \
+	Py_VISIT(type->tp_base);
-	}
-
-	VISIT(type->tp_dict);
-	VISIT(type->tp_cache);
-	VISIT(type->tp_mro);
-	VISIT(type->tp_bases);
-	VISIT(type->tp_base);
 
 	/* There's no need to visit type->tp_subclasses or
 	   ((PyHeapTypeObject *)type)->ht_slots, because they can't be involved
 	   in cycles; tp_subclasses is a list of weak references,
 	   and slots is a tuple of strings. */
 
-#undef VISIT
-
 	return 0;
 }
 
@@ -5805,20 +5788,10 @@ static int
 super_traverse(PyObject *self, visitproc visit, void *arg)
 {
 	superobject *su = (superobject *)self;
-	int err;
 
-#define VISIT(SLOT) \
+	Py_VISIT(su->obj);
-	if (SLOT) { \
+	Py_VISIT(su->type);
-		err = visit((PyObject *)(SLOT), arg); \
+	Py_VISIT(su->obj_type);
-		if (err) \
-			return err; \
-	}
-
-	VISIT(su->obj);
-	VISIT(su->type);
-	VISIT(su->obj_type);
-
-#undef VISIT
 
 	return 0;
 }

Objects/weakrefobject.c

@@ -109,8 +109,7 @@ weakref_dealloc(PyObject *self)
 static int
 gc_traverse(PyWeakReference *self, visitproc visit, void *arg)
 {
-    if (self->wr_callback != NULL)
+    Py_VISIT(self->wr_callback);
-        return visit(self->wr_callback, arg);
     return 0;
 }
 

Python/traceback.c

@@ -39,15 +39,9 @@ tb_dealloc(PyTracebackObject *tb)
 static int
 tb_traverse(PyTracebackObject *tb, visitproc visit, void *arg)
 {
-	int err = 0;
+	Py_VISIT(tb->tb_next);
-	if (tb->tb_next) {
+	Py_VISIT(tb->tb_frame);
-		err = visit((PyObject *)tb->tb_next, arg);
+	return 0;
-		if (err)
-			return err;
-	}
-	if (tb->tb_frame) 
-		err = visit((PyObject *)tb->tb_frame, arg);
-	return err;
 }
 
 static void