diff -r a62e9717e45c Include/object.h
--- a/Include/object.h	Wed Jun 11 20:37:52 2008 +0200
+++ b/Include/object.h	Wed Jun 11 21:13:04 2008 +0200
@@ -708,6 +708,20 @@ PyAPI_FUNC(void) _Py_AddToAllObjects(PyO
 #define Py_XINCREF(op) if ((op) == NULL) ; else Py_INCREF(op)
 #define Py_XDECREF(op) if ((op) == NULL) ; else Py_DECREF(op)
 
+/* Safely change an lvalue (e.g. a variable or struct member) from a
+ * PyObject * to another.
+ * When you are sure both the old and the new value are non-NULL,
+ * use Py_SETREF(). Otherwise, use Py_XSETREF().
+ */
+
+#define Py_SETREF(lvalue, rvalue) \
+    { PyObject *old = (lvalue), *new = (rvalue); Py_INCREF(new); \
+      (lvalue) = (new); Py_DECREF(old); }
+
+#define Py_XSETREF(lvalue, rvalue) \
+    { PyObject *old = (lvalue), *new = (rvalue); Py_XINCREF(new); \
+      (lvalue) = (new); Py_XDECREF(old); }
+
 /*
 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 a62e9717e45c Modules/_lsprof.c
--- a/Modules/_lsprof.c	Wed Jun 11 20:37:52 2008 +0200
+++ b/Modules/_lsprof.c	Wed Jun 11 21:13:04 2008 +0200
@@ -762,7 +762,6 @@ static int
 static int
 profiler_init(ProfilerObject *pObj, PyObject *args, PyObject *kw)
 {
-	PyObject *o;
 	PyObject *timer = NULL;
 	double timeunit = 0.0;
 	int subcalls = 1;
@@ -781,10 +780,7 @@ profiler_init(ProfilerObject *pObj, PyOb
 
 	if (setSubcalls(pObj, subcalls) < 0 || setBuiltins(pObj, builtins) < 0)
 		return -1;
-	o = pObj->externalTimer;
-	pObj->externalTimer = timer;
-	Py_XINCREF(timer);
-	Py_XDECREF(o);
+	Py_XSETREF(pObj->externalTimer, timer);
 	pObj->externalTimerUnit = timeunit;
 	return 0;
 }
diff -r a62e9717e45c Modules/_threadmodule.c
--- a/Modules/_threadmodule.c	Wed Jun 11 20:37:52 2008 +0200
+++ b/Modules/_threadmodule.c	Wed Jun 11 21:13:04 2008 +0200
@@ -278,9 +278,7 @@ _ldict(localobject *self)
 				return NULL;
 		}
 
-		Py_CLEAR(self->dict);
-		Py_INCREF(ldict);
-		self->dict = ldict; /* still borrowed */
+		Py_XSETREF(self->dict, ldict); /* still borrowed */
 
 		if (Py_TYPE(self)->tp_init != PyBaseObject_Type.tp_init &&
 		    Py_TYPE(self)->tp_init((PyObject*)self, 
@@ -294,9 +292,7 @@ _ldict(localobject *self)
 		
 	}
 	else if (self->dict != ldict) {
-		Py_CLEAR(self->dict);
-		Py_INCREF(ldict);
-		self->dict = ldict;
+		Py_XSETREF(self->dict, ldict);
 	}
 
 	return ldict;
diff -r a62e9717e45c Modules/readline.c
--- a/Modules/readline.c	Wed Jun 11 20:37:52 2008 +0200
+++ b/Modules/readline.c	Wed Jun 11 21:13:04 2008 +0200
@@ -178,10 +178,7 @@ set_hook(const char *funcname, PyObject 
 		*hook_var = NULL;
 	}
 	else if (PyCallable_Check(function)) {
-		PyObject *tmp = *hook_var;
-		Py_INCREF(function);
-		*hook_var = function;
-		Py_XDECREF(tmp);
+		Py_XSETREF(*hook_var, function);
 	}
 	else {
 		PyOS_snprintf(buf, sizeof(buf),
diff -r a62e9717e45c Modules/signalmodule.c
--- a/Modules/signalmodule.c	Wed Jun 11 20:37:52 2008 +0200
+++ b/Modules/signalmodule.c	Wed Jun 11 21:13:04 2008 +0200
@@ -580,9 +580,7 @@ PyInit_signal(void)
 	}
 	if (Handlers[SIGINT].func == DefaultHandler) {
 		/* Install default int handler */
-		Py_INCREF(IntHandler);
-		Py_DECREF(Handlers[SIGINT].func);
-		Handlers[SIGINT].func = IntHandler;
+		Py_SETREF(Handlers[SIGINT].func, IntHandler);
 		old_siginthandler = PyOS_setsig(SIGINT, signal_handler);
 	}
 
diff -r a62e9717e45c Modules/zlibmodule.c
--- a/Modules/zlibmodule.c	Wed Jun 11 20:37:52 2008 +0200
+++ b/Modules/zlibmodule.c	Wed Jun 11 21:13:05 2008 +0200
@@ -706,12 +706,8 @@ PyZlib_copy(compobject *self)
         goto error;
     }
 
-    Py_INCREF(self->unused_data);
-    Py_INCREF(self->unconsumed_tail);
-    Py_XDECREF(retval->unused_data);
-    Py_XDECREF(retval->unconsumed_tail);
-    retval->unused_data = self->unused_data;
-    retval->unconsumed_tail = self->unconsumed_tail;
+    Py_XSETREF(retval->unused_data, self->unused_data);
+    Py_XSETREF(retval->unconsumed_tail, self->unconsumed_tail);
 
     /* Mark it as being initialized */
     retval->is_initialised = 1;
@@ -757,12 +753,8 @@ PyZlib_uncopy(compobject *self)
         goto error;
     }
 
-    Py_INCREF(self->unused_data);
-    Py_INCREF(self->unconsumed_tail);
-    Py_XDECREF(retval->unused_data);
-    Py_XDECREF(retval->unconsumed_tail);
-    retval->unused_data = self->unused_data;
-    retval->unconsumed_tail = self->unconsumed_tail;
+    Py_XSETREF(retval->unused_data, self->unused_data);
+    Py_XSETREF(retval->unconsumed_tail, self->unconsumed_tail);
 
     /* Mark it as being initialized */
     retval->is_initialised = 1;