Fix another reincarnation of bug #1576657 in defaultdict.

Modules/_collectionsmodule.c

@@ -1075,7 +1075,7 @@ static PyTypeObject defdict_type; /* Forward */
 
 PyDoc_STRVAR(defdict_missing_doc,
 "__missing__(key) # Called by __getitem__ for missing key; pseudo-code:\n\
-  if self.default_factory is None: raise KeyError(key)\n\
+  if self.default_factory is None: raise KeyError((key,))\n\
   self[key] = value = self.default_factory()\n\
   return value\n\
 ");
@@ -1087,7 +1087,11 @@ defdict_missing(defdictobject *dd, PyObject *key)
 	PyObject *value;
 	if (factory == NULL || factory == Py_None) {
 		/* XXX Call dict.__missing__(key) */
-		PyErr_SetObject(PyExc_KeyError, key);
+		PyObject *tup;
+		tup = PyTuple_Pack(1, key);
+		if (!tup) return NULL;
+		PyErr_SetObject(PyExc_KeyError, tup);
+		Py_DECREF(tup);
 		return NULL;
 	}
 	value = PyEval_CallObject(factory, NULL);