Index: Objects/bytesobject.c
===================================================================
--- Objects/bytesobject.c	(Revision 58843)
+++ Objects/bytesobject.c	(Arbeitskopie)
@@ -923,6 +923,14 @@
 }
 
 static PyObject *
+bytes_str(PyObject *op)
+{
+	PyErr_SetString(PyExc_TypeError,
+			"str() argument must not be a buffer instance.");
+	return NULL;
+}
+
+static PyObject *
 bytes_richcompare(PyObject *self, PyObject *other, int op)
 {
     Py_ssize_t self_size, other_size;
@@ -3063,7 +3071,7 @@
     &bytes_as_mapping,                  /* tp_as_mapping */
     0,                                  /* tp_hash */
     0,                                  /* tp_call */
-    (reprfunc)bytes_repr,               /* tp_str */
+    (reprfunc)bytes_str,                /* tp_str */
     PyObject_GenericGetAttr,            /* tp_getattro */
     0,                                  /* tp_setattro */
     &bytes_as_buffer,                   /* tp_as_buffer */
Index: Objects/stringobject.c
===================================================================
--- Objects/stringobject.c	(Revision 58843)
+++ Objects/stringobject.c	(Arbeitskopie)
@@ -679,6 +679,14 @@
 	return PyString_Repr(op, 1);
 }
 
+static PyObject *
+string_str(PyObject *op)
+{
+	PyErr_SetString(PyExc_TypeError,
+			"str() argument must not be a byte instance.");
+	return NULL;
+}
+
 static Py_ssize_t
 string_length(PyStringObject *a)
 {
@@ -3096,7 +3104,7 @@
 	&string_as_mapping,			/* tp_as_mapping */
 	(hashfunc)string_hash, 			/* tp_hash */
 	0,					/* tp_call */
-	string_repr,				/* tp_str */
+	(reprfunc)string_str,			/* tp_str */
 	PyObject_GenericGetAttr,		/* tp_getattro */
 	0,					/* tp_setattro */
 	&string_as_buffer,			/* tp_as_buffer */
Index: Lib/test/test_bytes.py
===================================================================
--- Lib/test/test_bytes.py	(Revision 58843)
+++ Lib/test/test_bytes.py	(Arbeitskopie)
@@ -86,16 +86,22 @@
         self.assertRaises(ValueError, buffer, [sys.maxint+1])
         self.assertRaises(ValueError, buffer, [10**100])
 
-    def test_repr_str(self):
-        for f in str, repr:
-            self.assertEqual(f(buffer()), "buffer(b'')")
-            self.assertEqual(f(buffer([0])), "buffer(b'\\x00')")
-            self.assertEqual(f(buffer([0, 1, 254, 255])),
-                             "buffer(b'\\x00\\x01\\xfe\\xff')")
-            self.assertEqual(f(b"abc"), "b'abc'")
-            self.assertEqual(f(b"'"), '''b"'"''')
-            self.assertEqual(f(b"'\""), r"""b'\'"'""")
+    def test_repr(self):
+        self.assertEqual(repr(buffer()), "buffer(b'')")
+        self.assertEqual(repr(buffer([0])), "buffer(b'\\x00')")
+        self.assertEqual(repr(buffer([0, 1, 254, 255])),
+                         "buffer(b'\\x00\\x01\\xfe\\xff')")
+        self.assertEqual(repr(b"abc"), "b'abc'")
+        self.assertEqual(repr(b"'"), '''b"'"''')
+        self.assertEqual(repr(b"'\""), r"""b'\'"'""")
 
+    def test_str(self):
+        self.assertRaises(TypeError, str, buffer())
+        self.assertRaises(TypeError, str, buffer([0]))
+        self.assertRaises(TypeError, str, buffer([0, 1, 254, 255]))
+        self.assertRaises(TypeError, str, b"abc")
+        self.assertRaises(TypeError, str, b"'")
+        self.assertRaises(TypeError, str, b"'\"")
 
     def test_compare(self):
         b1 = buffer([1, 2, 3])
@@ -370,11 +376,6 @@
         b = buffer(buf)
         self.assertEqual(b, buffer(sample))
 
-    def test_to_str(self):
-        self.assertEqual(str(b''), "b''")
-        self.assertEqual(str(b'x'), "b'x'")
-        self.assertEqual(str(b'\x80'), "b'\\x80'")
-
     def test_from_int(self):
         b = buffer(0)
         self.assertEqual(b, buffer())