Check whether a string resize is necessary at the end

of PyString_DecodeEscape(). This prevents a call to
_PyString_Resize() for the empty string, which would
result in a PyErr_BadInternalCall(), because the
empty string has more than one reference.

This closes SF bug http://www.python.org/sf/603937

Lib/test/test_codecs.py

@@ -23,9 +23,16 @@ class UTF16Test(unittest.TestCase):
         f = reader(s)
         self.assertEquals(f.read(), u"spamspam")
 
+class EscapeDecodeTest(unittest.TestCase):
+    def test_empty_escape_decode(self):
+        self.assertEquals(codecs.escape_decode(""), ("", 0))
+
 
 def test_main():
-    test_support.run_unittest(UTF16Test)
+    suite = unittest.TestSuite()
+    suite.addTest(unittest.makeSuite(UTF16Test))
+    suite.addTest(unittest.makeSuite(EscapeDecodeTest))
+    test_support.run_suite(suite)
 
 
 if __name__ == "__main__":

Objects/stringobject.c

@@ -533,8 +533,8 @@ PyObject *PyString_DecodeEscape(const char *s,
 	char *p, *buf;
 	const char *end;
 	PyObject *v;
-	v = PyString_FromStringAndSize((char *)NULL, 
-				       recode_encoding ? 4*len:len);
+	int newlen = recode_encoding ? 4*len:len;
+	v = PyString_FromStringAndSize((char *)NULL, newlen);
 	if (v == NULL)
 		return NULL;
 	p = buf = PyString_AsString(v);
@@ -660,7 +660,8 @@ PyObject *PyString_DecodeEscape(const char *s,
 			break;
 		}
 	}
-	_PyString_Resize(&v, (int)(p - buf));
+	if (p-buf < newlen)
+		_PyString_Resize(&v, (int)(p - buf));
 	return v;
   failed:
 	Py_DECREF(v);