diff -r fa9933bf4ea0 Lib/test/test_bytes.py
--- a/Lib/test/test_bytes.py	Tue Dec 27 17:59:04 2016 +0200
+++ b/Lib/test/test_bytes.py	Thu Jan 05 09:38:27 2017 +0900
@@ -1,12 +1,13 @@
 """Unit tests for the bytes and bytearray types.
 
 XXX This is a mess.  Common tests should be unified with string_tests.py (and
 the latter should be modernized).
 """
 
+import array
 import os
 import re
 import sys
 import copy
 import functools
 import pickle
@@ -78,12 +79,24 @@
         b = self.type2test([Indexable(), Indexable(1), Indexable(254),
                             Indexable(255)])
         self.assertEqual(list(b), [0, 1, 254, 255])
         self.assertRaises(ValueError, self.type2test, [Indexable(-1)])
         self.assertRaises(ValueError, self.type2test, [Indexable(256)])
 
+    def test_from_buffer(self):
+        a = self.type2test(array.array('B', [1, 2, 3]))
+        self.assertEqual(b"\x01\x02\x03", a)
+
+        # http://bugs.python.org/issue29159
+        # Fallback when __index__ raises exception other than OverflowError
+        class B(bytes):
+            def __index__(self):
+                raise TypeError
+
+        self.assertEqual(b"foobar", self.type2test(B(b"foobar")))
+
     def test_from_ssize(self):
         self.assertEqual(self.type2test(0), b'')
         self.assertEqual(self.type2test(1), b'\x00')
         self.assertEqual(self.type2test(5), b'\x00\x00\x00\x00\x00')
         self.assertRaises(ValueError, self.type2test, -1)
 
diff -r fa9933bf4ea0 Objects/bytearrayobject.c
--- a/Objects/bytearrayobject.c	Tue Dec 27 17:59:04 2016 +0200
+++ b/Objects/bytearrayobject.c	Thu Jan 05 09:38:27 2017 +0900
@@ -795,24 +795,28 @@
     }
 
     /* Is it an int? */
     if (PyIndex_Check(arg)) {
         count = PyNumber_AsSsize_t(arg, PyExc_OverflowError);
         if (count == -1 && PyErr_Occurred()) {
-            return -1;
-        }
-        if (count < 0) {
-            PyErr_SetString(PyExc_ValueError, "negative count");
-            return -1;
+            if (PyErr_ExceptionMatches(PyExc_OverflowError))
+                return -1;
+            PyErr_Clear();  /* fall through */
         }
-        if (count > 0) {
-            if (PyByteArray_Resize((PyObject *)self, count))
+        else {
+            if (count < 0) {
+                PyErr_SetString(PyExc_ValueError, "negative count");
                 return -1;
-            memset(PyByteArray_AS_STRING(self), 0, count);
+            }
+            if (count > 0) {
+                if (PyByteArray_Resize((PyObject *)self, count))
+                    return -1;
+                memset(PyByteArray_AS_STRING(self), 0, count);
+            }
+            return 0;
         }
-        return 0;
     }
 
     /* Use the buffer API */
     if (PyObject_CheckBuffer(arg)) {
         Py_ssize_t size;
         Py_buffer view;
diff -r fa9933bf4ea0 Objects/bytesobject.c
--- a/Objects/bytesobject.c	Tue Dec 27 17:59:04 2016 +0200
+++ b/Objects/bytesobject.c	Thu Jan 05 09:38:27 2017 +0900
@@ -2590,22 +2590,26 @@
         return NULL;
     }
     /* Is it an integer? */
     if (PyIndex_Check(x)) {
         size = PyNumber_AsSsize_t(x, PyExc_OverflowError);
         if (size == -1 && PyErr_Occurred()) {
-            return NULL;
+            if (PyErr_ExceptionMatches(PyExc_OverflowError))
+                return NULL;
+            PyErr_Clear();  /* fall through */
         }
-        if (size < 0) {
-            PyErr_SetString(PyExc_ValueError, "negative count");
-            return NULL;
+        else {
+            if (size < 0) {
+                PyErr_SetString(PyExc_ValueError, "negative count");
+                return NULL;
+            }
+            new = _PyBytes_FromSize(size, 1);
+            if (new == NULL)
+                return NULL;
+            return new;
         }
-        new = _PyBytes_FromSize(size, 1);
-        if (new == NULL)
-            return NULL;
-        return new;
     }
 
     return PyBytes_FromObject(x);
 }
 
 static PyObject*