backport of 2.58:

  Fix SF bug #474538: Memory (reference) leak in poller.register (Dave Brueck)
  Replace some tortuous code that was trying to be clever but forgot to
  DECREF the key and value, by more longwinded but obviously correct
  code.

Modules/selectmodule.c

@@ -372,6 +372,7 @@ poll_register(pollObject *self, PyObject *args)
 {
 	PyObject *o, *key, *value;
 	int fd, events = POLLIN | POLLPRI | POLLOUT;
+	int err;
 
 	if (!PyArg_ParseTuple(args, "O|i:register", &o, &events)) {
 		return NULL;
@@ -382,11 +383,20 @@ poll_register(pollObject *self, PyObject *args)
 
 	/* Add entry to the internal dictionary: the key is the 
 	   file descriptor, and the value is the event mask. */
-	if ( (NULL == (key = PyInt_FromLong(fd))) ||
-	     (NULL == (value = PyInt_FromLong(events))) ||
-	     (PyDict_SetItem(self->dict, key, value)) == -1) {
+	key = PyInt_FromLong(fd);
+	if (key == NULL)
+		return NULL;
+	value = PyInt_FromLong(events);
+	if (value == NULL) {
+		Py_DECREF(key);
 		return NULL;
 	}
+	err = PyDict_SetItem(self->dict, key, value);
+	Py_DECREF(key);
+	Py_DECREF(value);
+	if (err < 0)
+		return NULL;
+
 	self->ufd_uptodate = 0;
 		       
 	Py_INCREF(Py_None);