diff -r 2a34cef7681b Objects/bytearrayobject.c
--- a/Objects/bytearrayobject.c	Mon Jul 11 14:21:58 2016 -0400
+++ b/Objects/bytearrayobject.c	Tue Jul 12 14:56:24 2016 +0800
@@ -882,62 +882,57 @@
     return -1;
 }
 
-/* Mostly copied from string_repr, but without the
+/* Mostly copied from PyBytes_Repr, but without the
    "smart quote" functionality. */
 static PyObject *
 bytearray_repr(PyByteArrayObject *self)
 {
     const char *quote_prefix = "bytearray(b";
     const char *quote_postfix = ")";
-    Py_ssize_t length = Py_SIZE(self);
-    /* 15 == strlen(quote_prefix) + 2 + strlen(quote_postfix) + 1 */
-    size_t newsize;
+    Py_ssize_t i, length = Py_SIZE(self);
+    Py_ssize_t newsize, squotes, dquotes;
+    unsigned char quote, *s, *p;
     PyObject *v;
-    Py_ssize_t i;
-    char *bytes;
-    char c;
-    char *p;
-    int quote;
-    char *test, *start;
-    char *buffer;
 
-    if (length > (PY_SSIZE_T_MAX - 15) / 4) {
-        PyErr_SetString(PyExc_OverflowError,
-            "bytearray object is too large to make repr");
-        return NULL;
+    squotes = dquotes = 0;
+    newsize = strlen(quote_prefix) + 2 + strlen(quote_postfix);  /* 2 quotes */
+    s = (unsigned char*)PyByteArray_AS_STRING(self);
+    for (i = 0; i < length; i++) {
+        Py_ssize_t incr = 1;
+        switch(s[i]) {
+        case '\'': squotes++; break;
+        case '"':  dquotes++; break;
+        case '\\': case '\t': case '\n': case '\r':
+            incr = 2; break;
+        default:
+            if (s[i] < ' ' || s[i] >= 0x7f)
+                incr = 4;
+        }
+        if (newsize > PY_SSIZE_T_MAX - incr)
+            goto overflow;
+        newsize += incr;
+    }
+    /* Figure out which quote to use; single is preferred */
+    quote = '\'';
+    if (dquotes == 0 && squotes > 0)
+        quote = '"';
+    if (squotes && quote == '\'') {
+        if (newsize > PY_SSIZE_T_MAX - squotes)
+            goto overflow;
+        newsize += squotes;
     }
 
-    newsize = 15 + length * 4;
-    buffer = PyObject_Malloc(newsize);
-    if (buffer == NULL) {
-        PyErr_NoMemory();
+    v = PyUnicode_New(newsize, 127);
+    if (v == NULL)
         return NULL;
-    }
+    p = PyUnicode_1BYTE_DATA(v);
 
-    /* Figure out which quote to use; single is preferred */
-    quote = '\'';
-    start = PyByteArray_AS_STRING(self);
-    for (test = start; test < start+length; ++test) {
-        if (*test == '"') {
-            quote = '\''; /* back to single */
-            break;
-        }
-        else if (*test == '\'')
-            quote = '"';
-    }
-
-    p = buffer;
     while (*quote_prefix)
         *p++ = *quote_prefix++;
     *p++ = quote;
-
-    bytes = PyByteArray_AS_STRING(self);
     for (i = 0; i < length; i++) {
-        /* There's at least enough room for a hex escape
-           and a closing quote. */
-        assert(newsize - (p - buffer) >= 5);
-        c = bytes[i];
-        if (c == '\'' || c == '\\')
+        unsigned char c = ((unsigned char *)PyByteArray_AS_STRING(self))[i];
+        if (c == quote || c == '\\')
             *p++ = '\\', *p++ = c;
         else if (c == '\t')
             *p++ = '\\', *p++ = 't';
@@ -945,8 +940,6 @@
             *p++ = '\\', *p++ = 'n';
         else if (c == '\r')
             *p++ = '\\', *p++ = 'r';
-        else if (c == 0)
-            *p++ = '\\', *p++ = 'x', *p++ = '0', *p++ = '0';
         else if (c < ' ' || c >= 0x7f) {
             *p++ = '\\';
             *p++ = 'x';
@@ -956,15 +949,16 @@
         else
             *p++ = c;
     }
-    assert(newsize - (p - buffer) >= 1);
     *p++ = quote;
-    while (*quote_postfix) {
-       *p++ = *quote_postfix++;
-    }
+    while (*quote_postfix)
+        *p++ = *quote_postfix++;
+    assert(_PyUnicode_CheckConsistency(v, 1));
+    return v;
 
-    v = PyUnicode_DecodeASCII(buffer, p - buffer, NULL);
-    PyObject_Free(buffer);
-    return v;
+ overflow:
+    PyErr_SetString(PyExc_OverflowError,
+                    "bytearray object is too large to make repr");
+    return NULL;
 }
 
 static PyObject *