From aa238dc73a2633fe4c0fb95ff50a4f0ac4a4af00 Mon Sep 17 00:00:00 2001
From: Siddharth Velankar <svelankar@users.noreply.github.com>
Date: Mon, 24 Jul 2017 21:49:15 -0400
Subject: [PATCH] bpo-30732: json.dumps() lacks information about
 RecursionError related to default function

---
 Modules/_json.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Modules/_json.c b/Modules/_json.c
index 6cc31c6e371224..f960867cc3beed 100644
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -1502,7 +1502,16 @@ encoder_listencode_obj(PyEncoderObject *s, _PyAccu *acc,
                 return -1;
             }
         }
+
         newobj = PyObject_CallFunctionObjArgs(s->defaultfn, obj, NULL);
+
+        if (obj != NULL && newobj != NULL && newobj->ob_type == obj->ob_type) {
+                PyErr_SetString(PyExc_TypeError, "Default serialization function returning same type");
+                Py_DECREF(newobj);
+                Py_XDECREF(ident);
+                return -1;
+        }
+
         if (newobj == NULL) {
             Py_XDECREF(ident);
             return -1;