PyObject_Init[Var] is almost always called from the PyObject_NEW[_VAR]

macros.  The 'op' argument is then the result from PyObject_MALLOC,
and that can of course be NULL.  In that case, PyObject_Init[Var]
would raise a SystemError with "NULL object passed to
PyObject_Init[Var]".  But there's nothing the caller of the macro can
do about this.  So PyObject_Init[Var] should call just PyErr_NoMemory.

Will backport.

Objects/object.c

@@ -109,11 +109,8 @@ _Py_NegativeRefcount(const char *fname, int lineno, PyObject *op)
 PyObject *
 PyObject_Init(PyObject *op, PyTypeObject *tp)
 {
-	if (op == NULL) {
-		PyErr_SetString(PyExc_SystemError,
-				"NULL object passed to PyObject_Init");
-		return op;
-  	}
+	if (op == NULL)
+		return PyErr_NoMemory();
 	/* Any changes should be reflected in PyObject_INIT (objimpl.h) */
 	op->ob_type = tp;
 	_Py_NewReference(op);
@@ -123,11 +120,8 @@ PyObject_Init(PyObject *op, PyTypeObject *tp)
 PyVarObject *
 PyObject_InitVar(PyVarObject *op, PyTypeObject *tp, int size)
 {
-	if (op == NULL) {
-		PyErr_SetString(PyExc_SystemError,
-				"NULL object passed to PyObject_InitVar");
-		return op;
-	}
+	if (op == NULL)
+		return (PyVarObject *) PyErr_NoMemory();
 	/* Any changes should be reflected in PyObject_INIT_VAR */
 	op->ob_size = size;
 	op->ob_type = tp;