From 004e03fb0c2febe2ec8afbd28ffcb3e980c63228 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Sun, 19 Mar 2017 19:38:42 +0200
Subject: bpo-29116: Improve error message for concatenating str with non-str.
 (#710)

---
 Objects/unicodeobject.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 503a59e..1a696cc 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -11282,7 +11282,16 @@ PyUnicode_Concat(PyObject *left, PyObject *right)
     Py_UCS4 maxchar, maxchar2;
     Py_ssize_t left_len, right_len, new_len;
 
-    if (ensure_unicode(left) < 0 || ensure_unicode(right) < 0)
+    if (ensure_unicode(left) < 0)
+        return NULL;
+
+    if (!PyUnicode_Check(right)) {
+        PyErr_Format(PyExc_TypeError,
+                     "can only concatenate str (not \"%.200s\") to str",
+                     right->ob_type->tp_name);
+        return NULL;
+    }
+    if (PyUnicode_READY(right) < 0)
         return NULL;
 
     /* Shortcuts */
-- 
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