diff -r 23a760bdd4b1 Include/object.h
--- a/Include/object.h	Fri Jan 17 09:29:24 2014 -0600
+++ b/Include/object.h	Sat Jan 18 00:03:42 2014 +0200
@@ -822,6 +822,38 @@
 #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 23a760bdd4b1 Modules/_csv.c
--- a/Modules/_csv.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/_csv.c	Sat Jan 18 00:03:42 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 23a760bdd4b1 Modules/_ctypes/_ctypes.c
--- a/Modules/_ctypes/_ctypes.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/_ctypes/_ctypes.c	Sat Jan 18 00:03:42 2014 +0200
@@ -384,8 +384,7 @@
         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);
@@ -863,8 +862,7 @@
         return -1;
     }
     Py_INCREF(proto);
-    Py_XDECREF(stgdict->proto);
-    stgdict->proto = proto;
+    Py_XREPLACE(stgdict->proto, proto);
     return 0;
 }
 
@@ -947,8 +945,7 @@
         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;
 }
@@ -1420,8 +1417,7 @@
         Py_DECREF((PyObject *)stgdict);
         return NULL;
     }
-    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!
@@ -1844,8 +1840,7 @@
         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;
 }
@@ -2353,8 +2348,7 @@
         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);
@@ -2496,8 +2490,7 @@
     }
     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);
@@ -3094,8 +3087,7 @@
         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;
diff -r 23a760bdd4b1 Modules/_curses_panel.c
--- a/Modules/_curses_panel.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/_curses_panel.c	Sat Jan 18 00:03:42 2014 +0200
@@ -283,8 +283,7 @@
         PyErr_SetString(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 23a760bdd4b1 Modules/_json.c
--- a/Modules/_json.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/_json.c	Sat Jan 18 00:03:42 2014 +0200
@@ -1699,8 +1699,7 @@
     }
     else if (PyUnicode_Check(s->encoding)) {
         PyObject *tmp = PyUnicode_AsEncodedString(s->encoding, NULL, NULL);
-        Py_DECREF(s->encoding);
-        s->encoding = tmp;
+        Py_REPLACE(s->encoding, tmp);
     }
     if (s->encoding == NULL)
         goto bail;
diff -r 23a760bdd4b1 Modules/_sqlite/connection.c
--- a/Modules/_sqlite/connection.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/_sqlite/connection.c	Sat Jan 18 00:03:42 2014 +0200
@@ -228,8 +228,8 @@
         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;
 }
@@ -817,8 +817,7 @@
         }
     }
 
-    Py_DECREF(self->statements);
-    self->statements = new_list;
+    Py_REPLACE(self->statements, new_list);
 }
 
 static void _pysqlite_drop_unused_cursor_references(pysqlite_Connection* self)
@@ -849,8 +848,7 @@
         }
     }
 
-    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 23a760bdd4b1 Modules/_sqlite/cursor.c
--- a/Modules/_sqlite/cursor.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/_sqlite/cursor.c	Sat Jan 18 00:03:42 2014 +0200
@@ -172,8 +172,7 @@
         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;
@@ -573,8 +572,8 @@
     }
 
     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;
         }
@@ -685,8 +684,7 @@
                 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 23a760bdd4b1 Modules/_sre.c
--- a/Modules/_sre.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/_sre.c	Sat Jan 18 00:03:42 2014 +0200
@@ -1992,8 +1992,7 @@
     if (!copy)
         return 0;
 
-    Py_DECREF(*object);
-    *object = copy;
+    Py_REPLACE(*object, copy);
 
     return 1; /* success */
 }
diff -r 23a760bdd4b1 Modules/bz2module.c
--- a/Modules/bz2module.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/bz2module.c	Sat Jan 18 00:03:42 2014 +0200
@@ -1952,9 +1952,8 @@
             self->running = 0;
             input_left += bzs->avail_in;
             if (input_left != 0) {
-                Py_DECREF(self->unused_data);
-                self->unused_data =
-                    PyString_FromStringAndSize(bzs->next_in, input_left);
+                Py_REPLACE(self->unused_data,
+                           PyString_FromStringAndSize(bzs->next_in, input_left));
                 if (self->unused_data == NULL)
                     goto error;
             }
diff -r 23a760bdd4b1 Modules/cPickle.c
--- a/Modules/cPickle.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/cPickle.c	Sat Jan 18 00:03:42 2014 +0200
@@ -690,8 +690,7 @@
     }
     if (! str) return -1;
 
-    Py_XDECREF(self->last_string);
-    self->last_string = str;
+    Py_XREPLACE(self->last_string, str);
 
     if (! (*s = PyString_AsString(str))) return -1;
 
@@ -717,8 +716,7 @@
     if ((str_size = PyString_Size(str)) < 0)
         return -1;
 
-    Py_XDECREF(self->last_string);
-    self->last_string = str;
+    Py_XREPLACE(self->last_string, str);
 
     if (! (*s = PyString_AsString(str)))
         return -1;
@@ -5633,15 +5631,13 @@
 {
 
     if (!strcmp(name, "persistent_load")) {
-        Py_XDECREF(self->pers_func);
-        self->pers_func = value;
+        Py_XREPLACE(self->pers_func, value);
         Py_XINCREF(value);
         return 0;
     }
 
     if (!strcmp(name, "find_global")) {
-        Py_XDECREF(self->find_class);
-        self->find_class = value;
+        Py_XREPLACE(self->find_class, value);
         Py_XINCREF(value);
         return 0;
     }
@@ -5658,8 +5654,7 @@
                             "memo must be a dictionary");
             return -1;
         }
-        Py_XDECREF(self->memo);
-        self->memo = value;
+        Py_XREPLACE(self->memo, value);
         Py_INCREF(value);
         return 0;
     }
diff -r 23a760bdd4b1 Modules/itertoolsmodule.c
--- a/Modules/itertoolsmodule.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/itertoolsmodule.c	Sat Jan 18 00:03:42 2014 +0200
@@ -494,8 +494,7 @@
         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 23a760bdd4b1 Modules/signalmodule.c
--- a/Modules/signalmodule.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/signalmodule.c	Sat Jan 18 00:03:42 2014 +0200
@@ -621,8 +621,7 @@
     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 23a760bdd4b1 Modules/zipimport.c
--- a/Modules/zipimport.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/zipimport.c	Sat Jan 18 00:03:42 2014 +0200
@@ -830,8 +830,7 @@
                 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 23a760bdd4b1 Modules/zlibmodule.c
--- a/Modules/zlibmodule.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Modules/zlibmodule.c	Sat Jan 18 00:03:42 2014 +0200
@@ -491,8 +491,7 @@
                       PyString_AS_STRING(self->unused_data), old_size);
             Py_MEMCPY(PyString_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;
         }
     }
@@ -504,8 +503,7 @@
                 (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 23a760bdd4b1 Objects/descrobject.c
--- a/Objects/descrobject.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Objects/descrobject.c	Sat Jan 18 00:03:42 2014 +0200
@@ -1332,8 +1332,7 @@
         PyObject *get_doc = PyObject_GetAttrString(get, "__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 23a760bdd4b1 Objects/exceptions.c
--- a/Objects/exceptions.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Objects/exceptions.c	Sat Jan 18 00:03:42 2014 +0200
@@ -58,8 +58,7 @@
     if (!_PyArg_NoKeywords(Py_TYPE(self)->tp_name, kwds))
         return -1;
 
-    Py_DECREF(self->args);
-    self->args = args;
+    Py_REPLACE(self->args, args);
     Py_INCREF(self->args);
 
     if (PyTuple_GET_SIZE(self->args) == 1) {
@@ -627,8 +626,7 @@
         if (!subslice)
             return -1;
 
-        Py_DECREF(self->args);  /* replacing args */
-        self->args = subslice;
+        Py_REPLACE(self->args, subslice);
     }
     return 0;
 }
diff -r 23a760bdd4b1 Objects/fileobject.c
--- a/Objects/fileobject.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Objects/fileobject.c	Sat Jan 18 00:03:42 2014 +0200
@@ -574,10 +574,8 @@
         oerrors = Py_None;
         Py_INCREF(Py_None);
     }
-    Py_DECREF(file->f_encoding);
-    file->f_encoding = str;
-    Py_DECREF(file->f_errors);
-    file->f_errors = oerrors;
+    Py_REPLACE(file->f_encoding, str);
+    Py_REPLACE(file->f_errors, oerrors);
     return 1;
 }
 
diff -r 23a760bdd4b1 Objects/frameobject.c
--- a/Objects/frameobject.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Objects/frameobject.c	Sat Jan 18 00:03:42 2014 +0200
@@ -859,8 +859,7 @@
             }
         } 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 23a760bdd4b1 Objects/funcobject.c
--- a/Objects/funcobject.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Objects/funcobject.c	Sat Jan 18 00:03:42 2014 +0200
@@ -116,8 +116,7 @@
         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;
 }
 
@@ -149,8 +148,7 @@
                      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;
 }
 
@@ -430,8 +428,7 @@
 
     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 23a760bdd4b1 Objects/stringobject.c
--- a/Objects/stringobject.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Objects/stringobject.c	Sat Jan 18 00:03:42 2014 +0200
@@ -3862,8 +3862,7 @@
         return;
     }
     v = string_concat((PyStringObject *) *pv, w);
-    Py_DECREF(*pv);
-    *pv = v;
+    Py_REPLACE(*pv, v);
 }
 
 void
@@ -4748,8 +4747,7 @@
     t = PyDict_GetItem(interned, (PyObject *)s);
     if (t) {
         Py_INCREF(t);
-        Py_DECREF(*p);
-        *p = t;
+        Py_REPLACE(*p, t);
         return;
     }
 
diff -r 23a760bdd4b1 Objects/typeobject.c
--- a/Objects/typeobject.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Objects/typeobject.c	Sat Jan 18 00:03:42 2014 +0200
@@ -166,8 +166,7 @@
            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 */
@@ -2528,8 +2527,7 @@
         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 23a760bdd4b1 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Objects/unicodeobject.c	Sat Jan 18 00:03:42 2014 +0200
@@ -436,8 +436,7 @@
             return -1;
         Py_UNICODE_COPY(w->str, v->str,
                         length < v->length ? length : v->length);
-        Py_DECREF(*unicode);
-        *unicode = w;
+        Py_REPLACE(*unicode, w);
         return 0;
     }
 
diff -r 23a760bdd4b1 Python/_warnings.c
--- a/Python/_warnings.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Python/_warnings.c	Sat Jan 18 00:03:42 2014 +0200
@@ -528,8 +528,7 @@
                     goto handle_error;
                 }
                 else if (!is_true) {
-                    Py_DECREF(*filename);
-                    *filename = PyString_FromString("__main__");
+                    Py_REPLACE(*filename, PyString_FromString("__main__"));
                     if (*filename == NULL)
                         goto handle_error;
                 }
diff -r 23a760bdd4b1 Python/ceval.c
--- a/Python/ceval.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Python/ceval.c	Sat Jan 18 00:03:42 2014 +0200
@@ -2695,8 +2695,7 @@
                 Py_INCREF(self);
                 func = PyMethod_GET_FUNCTION(func);
                 Py_INCREF(func);
-                Py_DECREF(*pfunc);
-                *pfunc = self;
+                Py_REPLACE(*pfunc, self);
                 na++;
             } else
                 Py_INCREF(func);
@@ -4031,8 +4030,7 @@
             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 23a760bdd4b1 Python/compile.c
--- a/Python/compile.c	Fri Jan 17 09:29:24 2014 -0600
+++ b/Python/compile.c	Sat Jan 18 00:03:42 2014 +0200
@@ -1455,8 +1455,7 @@
     if (!compiler_enter_scope(c, s->v.ClassDef.name, (void *)s,
                               s->lineno))
         return 0;
-    Py_XDECREF(c->u->u_private);
-    c->u->u_private = s->v.ClassDef.name;
+    Py_XREPLACE(c->u->u_private, s->v.ClassDef.name);
     Py_INCREF(c->u->u_private);
     str = PyString_InternFromString("__name__");
     if (!str || !compiler_nameop(c, str, Load)) {