diff -r 64401c6656b5 Include/object.h
--- a/Include/object.h	Fri Jan 17 12:08:49 2014 -0800
+++ b/Include/object.h	Sat Jan 18 00:03:35 2014 +0200
@@ -824,6 +824,38 @@
 #define Py_XINCREF(op) do { if ((op) == NULL) ; else Py_INCREF(op); } while (0)
 #define Py_XDECREF(op) do { if ((op) == NULL) ; else Py_DECREF(op); } while (0)
 
+/* Safely decref `op` and set `op` to `op2`.
+ *
+ * As in case of Py_CLEAR "the obvious" code can be deadly:
+ *
+ *     Py_DECREF(op);
+ *     op = op2;
+ *
+ * The safe way is:
+ *
+ *      Py_REPLACE(op, op2);
+ *
+ * That arranges to set `op` to `op2` _before_ decref'ing, so that any code
+ * triggered as a side-effect of `op` getting torn down no longer believes
+ * `op` points to a valid object.
+ *
+ * Py_XREPLACE is a variant of Py_REPLACE which calls Py_XDECREF.
+ */
+
+#define Py_REPLACE(op, op2)                     \
+    do {                                        \
+        PyObject *_py_tmp = (PyObject *)(op);   \
+        (op) = (op2);                           \
+        Py_DECREF(_py_tmp);                     \
+    } while (0)
+
+#define Py_XREPLACE(op, op2)                    \
+    do {                                        \
+        PyObject *_py_tmp = (PyObject *)(op);   \
+        (op) = (op2);                           \
+        Py_XDECREF(_py_tmp);                    \
+    } while (0)
+
 /*
 These are provided as conveniences to Python runtime embedders, so that
 they can have object code that is not dependent on Python compilation flags.
diff -r 64401c6656b5 Modules/_csv.c
--- a/Modules/_csv.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/_csv.c	Sat Jan 18 00:03:35 2014 +0200
@@ -770,8 +770,7 @@
 static int
 parse_reset(ReaderObj *self)
 {
-    Py_XDECREF(self->fields);
-    self->fields = PyList_New(0);
+    Py_XREPLACE(self->fields, PyList_New(0));
     if (self->fields == NULL)
         return -1;
     self->field_len = 0;
diff -r 64401c6656b5 Modules/_ctypes/_ctypes.c
--- a/Modules/_ctypes/_ctypes.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/_ctypes/_ctypes.c	Sat Jan 18 00:03:35 2014 +0200
@@ -349,8 +349,7 @@
         Py_DECREF((PyObject *)dict);
         return NULL;
     }
-    Py_DECREF(result->tp_dict);
-    result->tp_dict = (PyObject *)dict;
+    Py_REPLACE(result->tp_dict, (PyObject *)dict);
     dict->format = _ctypes_alloc_format_string(NULL, "B");
     if (dict->format == NULL) {
         Py_DECREF(result);
@@ -825,8 +824,7 @@
         return -1;
     }
     Py_INCREF(proto);
-    Py_XDECREF(stgdict->proto);
-    stgdict->proto = proto;
+    Py_XREPLACE(stgdict->proto, proto);
     return 0;
 }
 
@@ -909,8 +907,7 @@
         Py_DECREF((PyObject *)stgdict);
         return NULL;
     }
-    Py_DECREF(result->tp_dict);
-    result->tp_dict = (PyObject *)stgdict;
+    Py_REPLACE(result->tp_dict, (PyObject *)stgdict);
 
     return (PyObject *)result;
 }
@@ -1358,8 +1355,7 @@
     /* replace the class dict by our updated spam dict */
     if (-1 == PyDict_Update((PyObject *)stgdict, result->tp_dict))
         goto error;
-    Py_DECREF(result->tp_dict);
-    result->tp_dict = (PyObject *)stgdict;
+    Py_REPLACE(result->tp_dict, (PyObject *)stgdict);
 
     /* Special case for character arrays.
        A permanent annoyance: char arrays are also strings!
@@ -1788,8 +1784,7 @@
         Py_DECREF((PyObject *)stgdict);
         return NULL;
     }
-    Py_DECREF(result->tp_dict);
-    result->tp_dict = (PyObject *)stgdict;
+    Py_REPLACE(result->tp_dict, (PyObject *)stgdict);
 
     return (PyObject *)result;
 }
@@ -1917,8 +1912,7 @@
         Py_DECREF((PyObject *)stgdict);
         return NULL;
     }
-    Py_DECREF(result->tp_dict);
-    result->tp_dict = (PyObject *)stgdict;
+    Py_REPLACE(result->tp_dict, (PyObject *)stgdict);
 
     /* Install from_param class methods in ctypes base classes.
        Overrides the PyCSimpleType_from_param generic method.
@@ -2277,8 +2271,7 @@
         Py_DECREF((PyObject *)stgdict);
         return NULL;
     }
-    Py_DECREF(result->tp_dict);
-    result->tp_dict = (PyObject *)stgdict;
+    Py_REPLACE(result->tp_dict, (PyObject *)stgdict);
 
     if (-1 == make_funcptrtype_dict(stgdict)) {
         Py_DECREF(result);
@@ -2412,8 +2405,7 @@
     }
     ob = PyCData_GetContainer(target);
     if (ob->b_objects == NULL || !PyDict_CheckExact(ob->b_objects)) {
-        Py_XDECREF(ob->b_objects);
-        ob->b_objects = keep; /* refcount consumed */
+        Py_XREPLACE(ob->b_objects, keep); /* refcount consumed */
         return 0;
     }
     key = unique_key(target, index);
@@ -2984,8 +2976,7 @@
         converters = converters_from_argtypes(ob);
         if (!converters)
             return -1;
-        Py_XDECREF(self->converters);
-        self->converters = converters;
+        Py_XREPLACE(self->converters, converters);
         Py_XDECREF(self->argtypes);
         Py_INCREF(ob);
         self->argtypes = ob;
@@ -5105,8 +5096,7 @@
         return -1;
 
     bself = (PyBaseExceptionObject *)self;
-    Py_DECREF(bself->args);
-    bself->args = args;
+    Py_REPLACE(bself->args, args);
     Py_INCREF(bself->args);
 
     return 0;
diff -r 64401c6656b5 Modules/_curses_panel.c
--- a/Modules/_curses_panel.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/_curses_panel.c	Sat Jan 18 00:03:35 2014 +0200
@@ -312,8 +312,7 @@
         PyErr_SetString(_curses_panelstate_global->PyCursesError, "replace_panel() returned ERR");
         return NULL;
     }
-    Py_DECREF(po->wo);
-    po->wo = temp;
+    Py_REPLACE(po->wo, temp);
     Py_INCREF(po->wo);
     Py_INCREF(Py_None);
     return Py_None;
diff -r 64401c6656b5 Modules/_sqlite/connection.c
--- a/Modules/_sqlite/connection.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/_sqlite/connection.c	Sat Jan 18 00:03:35 2014 +0200
@@ -185,8 +185,8 @@
         node = node->next;
     }
 
-    Py_DECREF(self->statement_cache);
-    self->statement_cache = (pysqlite_Cache*)PyObject_CallFunction((PyObject*)&pysqlite_CacheType, "O", self);
+    Py_REPLACE(self->statement_cache,
+               (pysqlite_Cache *)PyObject_CallFunction((PyObject *)&pysqlite_CacheType, "O", self));
     Py_DECREF(self);
     self->statement_cache->decref_factory = 0;
 }
@@ -751,8 +751,7 @@
         }
     }
 
-    Py_DECREF(self->statements);
-    self->statements = new_list;
+    Py_REPLACE(self->statements, new_list);
 }
 
 static void _pysqlite_drop_unused_cursor_references(pysqlite_Connection* self)
@@ -783,8 +782,7 @@
         }
     }
 
-    Py_DECREF(self->cursors);
-    self->cursors = new_list;
+    Py_REPLACE(self->cursors, new_list);
 }
 
 PyObject* pysqlite_connection_create_function(pysqlite_Connection* self, PyObject* args, PyObject* kwargs)
diff -r 64401c6656b5 Modules/_sqlite/cursor.c
--- a/Modules/_sqlite/cursor.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/_sqlite/cursor.c	Sat Jan 18 00:03:35 2014 +0200
@@ -171,8 +171,7 @@
         return 0;
     }
 
-    Py_XDECREF(self->row_cast_map);
-    self->row_cast_map = PyList_New(0);
+    Py_XREPLACE(self->row_cast_map, PyList_New(0));
 
     for (i = 0; i < sqlite3_column_count(self->statement->st); i++) {
         converter = NULL;
@@ -541,8 +540,8 @@
     }
 
     if (self->statement->in_use) {
-        Py_DECREF(self->statement);
-        self->statement = PyObject_New(pysqlite_Statement, &pysqlite_StatementType);
+        Py_REPLACE(self->statement,
+                   PyObject_New(pysqlite_Statement, &pysqlite_StatementType));
         if (!self->statement) {
             goto error;
         }
@@ -654,8 +653,7 @@
                 numcols = sqlite3_column_count(self->statement->st);
                 Py_END_ALLOW_THREADS
 
-                Py_DECREF(self->description);
-                self->description = PyTuple_New(numcols);
+                Py_REPLACE(self->description, PyTuple_New(numcols));
                 if (!self->description) {
                     goto error;
                 }
diff -r 64401c6656b5 Modules/_sre.c
--- a/Modules/_sre.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/_sre.c	Sat Jan 18 00:03:35 2014 +0200
@@ -1989,8 +1989,7 @@
     if (!copy)
         return 0;
 
-    Py_DECREF(*object);
-    *object = copy;
+    Py_REPLACE(*object, copy);
 
     return 1; /* success */
 }
diff -r 64401c6656b5 Modules/itertoolsmodule.c
--- a/Modules/itertoolsmodule.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/itertoolsmodule.c	Sat Jan 18 00:03:35 2014 +0200
@@ -636,8 +636,7 @@
         link = teedataobject_jumplink(to->dataobj);
         if (link == NULL)
             return NULL;
-        Py_DECREF(to->dataobj);
-        to->dataobj = (teedataobject *)link;
+        Py_REPLACE(to->dataobj, (teedataobject *)link);
         to->index = 0;
     }
     value = teedataobject_getitem(to->dataobj, to->index);
diff -r 64401c6656b5 Modules/signalmodule.c
--- a/Modules/signalmodule.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/signalmodule.c	Sat Jan 18 00:03:35 2014 +0200
@@ -1041,8 +1041,7 @@
     if (Handlers[SIGINT].func == DefaultHandler) {
         /* Install default int handler */
         Py_INCREF(IntHandler);
-        Py_DECREF(Handlers[SIGINT].func);
-        Handlers[SIGINT].func = IntHandler;
+        Py_REPLACE(Handlers[SIGINT].func, IntHandler);
         old_siginthandler = PyOS_setsig(SIGINT, signal_handler);
     }
 
diff -r 64401c6656b5 Modules/zipimport.c
--- a/Modules/zipimport.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/zipimport.c	Sat Jan 18 00:03:35 2014 +0200
@@ -188,8 +188,7 @@
             tmp = PyUnicode_FromFormat("%U%c", self->prefix, SEP);
             if (tmp == NULL)
                 goto error;
-            Py_DECREF(self->prefix);
-            self->prefix = tmp;
+            Py_REPLACE(self->prefix, tmp);
         }
     }
     else
@@ -956,8 +955,7 @@
                 fclose(fp);
                 return NULL;
             }
-            Py_XDECREF(self->files);  /* free the old value. */
-            self->files = files;
+            Py_XREPLACE(self->files, files);
         }
         Py_DECREF(stat_now);
     }  /* stat succeeded */
diff -r 64401c6656b5 Modules/zlibmodule.c
--- a/Modules/zlibmodule.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Modules/zlibmodule.c	Sat Jan 18 00:03:35 2014 +0200
@@ -585,8 +585,7 @@
                       PyBytes_AS_STRING(self->unused_data), old_size);
             Py_MEMCPY(PyBytes_AS_STRING(new_data) + old_size,
                       self->zst.next_in, self->zst.avail_in);
-            Py_DECREF(self->unused_data);
-            self->unused_data = new_data;
+            Py_REPLACE(self->unused_data, new_data);
             self->zst.avail_in = 0;
         }
     }
@@ -598,8 +597,7 @@
                 (char *)self->zst.next_in, self->zst.avail_in);
         if (new_data == NULL)
             return -1;
-        Py_DECREF(self->unconsumed_tail);
-        self->unconsumed_tail = new_data;
+        Py_REPLACE(self->unconsumed_tail, new_data);
     }
     return 0;
 }
diff -r 64401c6656b5 Objects/bytesobject.c
--- a/Objects/bytesobject.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Objects/bytesobject.c	Sat Jan 18 00:03:35 2014 +0200
@@ -2849,8 +2849,7 @@
         return;
     }
     v = bytes_concat(*pv, w);
-    Py_DECREF(*pv);
-    *pv = v;
+    Py_REPLACE(*pv, v);
 }
 
 void
diff -r 64401c6656b5 Objects/descrobject.c
--- a/Objects/descrobject.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Objects/descrobject.c	Sat Jan 18 00:03:35 2014 +0200
@@ -1444,8 +1444,7 @@
         PyObject *get_doc = _PyObject_GetAttrId(get, &PyId___doc__);
         if (get_doc) {
             if (Py_TYPE(self) == &PyProperty_Type) {
-                Py_XDECREF(prop->prop_doc);
-                prop->prop_doc = get_doc;
+                Py_XREPLACE(prop->prop_doc, get_doc);
             }
             else {
                 /* If this is a property subclass, put __doc__
diff -r 64401c6656b5 Objects/exceptions.c
--- a/Objects/exceptions.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Objects/exceptions.c	Sat Jan 18 00:03:35 2014 +0200
@@ -239,8 +239,7 @@
     }
 
     Py_XINCREF(tb);
-    Py_XDECREF(self->traceback);
-    self->traceback = tb;
+    Py_XREPLACE(self->traceback, tb);
     return 0;
 }
 
diff -r 64401c6656b5 Objects/frameobject.c
--- a/Objects/frameobject.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Objects/frameobject.c	Sat Jan 18 00:03:35 2014 +0200
@@ -832,8 +832,7 @@
             }
         } else if (values[j] != value) {
             Py_XINCREF(value);
-            Py_XDECREF(values[j]);
-            values[j] = value;
+            Py_XREPLACE(values[j], value);
         }
         Py_XDECREF(value);
     }
diff -r 64401c6656b5 Objects/funcobject.c
--- a/Objects/funcobject.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Objects/funcobject.c	Sat Jan 18 00:03:35 2014 +0200
@@ -128,8 +128,7 @@
         PyErr_SetString(PyExc_SystemError, "non-tuple default args");
         return -1;
     }
-    Py_XDECREF(((PyFunctionObject *) op) -> func_defaults);
-    ((PyFunctionObject *) op) -> func_defaults = defaults;
+    Py_XREPLACE(((PyFunctionObject *)op)->func_defaults, defaults);
     return 0;
 }
 
@@ -160,8 +159,7 @@
                         "non-dict keyword only default args");
         return -1;
     }
-    Py_XDECREF(((PyFunctionObject *)op) -> func_kwdefaults);
-    ((PyFunctionObject *) op) -> func_kwdefaults = defaults;
+    Py_XREPLACE(((PyFunctionObject *)op)->func_kwdefaults, defaults);
     return 0;
 }
 
@@ -193,8 +191,7 @@
                      closure->ob_type->tp_name);
         return -1;
     }
-    Py_XDECREF(((PyFunctionObject *) op) -> func_closure);
-    ((PyFunctionObject *) op) -> func_closure = closure;
+    Py_XREPLACE(((PyFunctionObject *)op)->func_closure, closure);
     return 0;
 }
 
@@ -225,8 +222,7 @@
                         "non-dict annotations");
         return -1;
     }
-    Py_XDECREF(((PyFunctionObject *)op) -> func_annotations);
-    ((PyFunctionObject *) op) -> func_annotations = annotations;
+    Py_XREPLACE(((PyFunctionObject *)op)->func_annotations, annotations);
     return 0;
 }
 
@@ -532,8 +528,7 @@
 
     if (name != Py_None) {
         Py_INCREF(name);
-        Py_DECREF(newfunc->func_name);
-        newfunc->func_name = name;
+        Py_REPLACE(newfunc->func_name, name);
     }
     if (defaults != Py_None) {
         Py_INCREF(defaults);
diff -r 64401c6656b5 Objects/rangeobject.c
--- a/Objects/rangeobject.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Objects/rangeobject.c	Sat Jan 18 00:03:35 2014 +0200
@@ -1229,8 +1229,7 @@
     result = PyNumber_Add(r->start, product);
     Py_DECREF(product);
     if (result) {
-        Py_DECREF(r->index);
-        r->index = new_index;
+        Py_REPLACE(r->index, new_index);
     }
     else {
         Py_DECREF(new_index);
diff -r 64401c6656b5 Objects/typeobject.c
--- a/Objects/typeobject.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Objects/typeobject.c	Sat Jan 18 00:03:35 2014 +0200
@@ -181,8 +181,7 @@
            are borrowed reference */
         for (i = 0; i < (1 << MCACHE_SIZE_EXP); i++) {
             method_cache[i].value = NULL;
-            Py_XDECREF(method_cache[i].name);
-            method_cache[i].name = Py_None;
+            Py_XREPLACE(method_cache[i].name, Py_None);
             Py_INCREF(Py_None);
         }
         /* mark all version tags as invalid */
@@ -328,8 +327,7 @@
 
     et = (PyHeapTypeObject*)type;
     Py_INCREF(value);
-    Py_DECREF(et->ht_qualname);
-    et->ht_qualname = value;
+    Py_REPLACE(et->ht_qualname, value);
     return 0;
 }
 
@@ -2573,8 +2571,7 @@
         method_cache[h].version = type->tp_version_tag;
         method_cache[h].value = res;  /* borrowed */
         Py_INCREF(name);
-        Py_DECREF(method_cache[h].name);
-        method_cache[h].name = name;
+        Py_REPLACE(method_cache[h].name, name);
     }
     return res;
 }
diff -r 64401c6656b5 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Objects/unicodeobject.c	Sat Jan 18 00:03:35 2014 +0200
@@ -1603,8 +1603,7 @@
         _Py_INCREF_UNICODE_EMPTY();
         if (!unicode_empty)
             return -1;
-        Py_DECREF(*p_unicode);
-        *p_unicode = unicode_empty;
+        Py_REPLACE(*p_unicode, unicode_empty);
         return 0;
     }
 
@@ -1612,8 +1611,7 @@
         PyObject *copy = resize_copy(unicode, length);
         if (copy == NULL)
             return -1;
-        Py_DECREF(*p_unicode);
-        *p_unicode = copy;
+        Py_REPLACE(*p_unicode, copy);
         return 0;
     }
 
@@ -1658,8 +1656,7 @@
     if (result == NULL)
         return -1;
     _PyUnicode_FastCopyCharacters(result, 0, *p_unicode, 0, length);
-    Py_DECREF(*p_unicode);
-    *p_unicode = result;
+    Py_REPLACE(*p_unicode, result);
     return 0;
 }
 
@@ -12879,8 +12876,7 @@
             return -1;
         _PyUnicode_FastCopyCharacters(newbuffer, 0,
                                       writer->buffer, 0, writer->pos);
-        Py_DECREF(writer->buffer);
-        writer->buffer = newbuffer;
+        Py_REPLACE(writer->buffer, newbuffer);
         _PyUnicodeWriter_Update(writer);
     }
     return 0;
diff -r 64401c6656b5 Python/_warnings.c
--- a/Python/_warnings.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Python/_warnings.c	Sat Jan 18 00:03:35 2014 +0200
@@ -545,8 +545,7 @@
                     goto handle_error;
                 }
                 else if (!is_true) {
-                    Py_DECREF(*filename);
-                    *filename = PyUnicode_FromString("__main__");
+                    Py_REPLACE(*filename, PyUnicode_FromString("__main__"));
                     if (*filename == NULL)
                         goto handle_error;
                 }
diff -r 64401c6656b5 Python/ceval.c
--- a/Python/ceval.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Python/ceval.c	Sat Jan 18 00:03:35 2014 +0200
@@ -2709,8 +2709,7 @@
                 Py_INCREF(self);
                 func = PyMethod_GET_FUNCTION(func);
                 Py_INCREF(func);
-                Py_DECREF(*pfunc);
-                *pfunc = self;
+                Py_REPLACE(*pfunc, self);
                 na++;
                 /* n++; */
             } else
@@ -4079,8 +4078,7 @@
             Py_INCREF(self);
             func = PyMethod_GET_FUNCTION(func);
             Py_INCREF(func);
-            Py_DECREF(*pfunc);
-            *pfunc = self;
+            Py_REPLACE(*pfunc, self);
             na++;
             n++;
         } else
diff -r 64401c6656b5 Python/compile.c
--- a/Python/compile.c	Fri Jan 17 12:08:49 2014 -0800
+++ b/Python/compile.c	Sat Jan 18 00:03:35 2014 +0200
@@ -1659,8 +1659,7 @@
     {
         /* use the class name for name mangling */
         Py_INCREF(s->v.ClassDef.name);
-        Py_XDECREF(c->u->u_private);
-        c->u->u_private = s->v.ClassDef.name;
+        Py_XREPLACE(c->u->u_private, s->v.ClassDef.name);
         /* force it to have one mandatory argument */
         c->u->u_argcount = 1;
         /* load the first argument (__locals__) ... */