Fix #1753395.

Objects/typeobject.c

@@ -1561,28 +1561,16 @@ static PyGetSetDef subtype_getsets_weakref_only[] = {
 static int
 valid_identifier(PyObject *s)
 {
-	Py_UNICODE *p;
-	Py_ssize_t i, n;
-
 	if (!PyUnicode_Check(s)) {
 		PyErr_Format(PyExc_TypeError,
 			     "__slots__ items must be strings, not '%.200s'",
 			     Py_Type(s)->tp_name);
 		return 0;
 	}
-	p = PyUnicode_AS_UNICODE(s);
-	n = PyUnicode_GET_SIZE(s);
-	/* We must reject an empty name.  As a hack, we bump the
-	   length to 1 so that the loop will balk on the trailing \0. */
-	if (n == 0)
-		n = 1;
-	for (i = 0; i < n; i++, p++) {
-		if (*p > 127 ||
-		    (!(i == 0 ? isalpha(*p) : isalnum(*p)) && *p != '_')) {
-			PyErr_SetString(PyExc_TypeError,
-					"__slots__ must be identifiers");
-			return 0;
-		}
+	if (!PyUnicode_IsIdentifier(s)) {
+		PyErr_SetString(PyExc_TypeError,
+				"__slots__ must be identifiers");
+		return 0;
 	}
 	return 1;
 }