make sure that bytearray methods return a new bytearray even if there is no change

Fixes #4348
Reviewed by Brett

Lib/test/test_bytes.py

@@ -721,6 +721,16 @@ class ByteArrayTest(BaseBytesTest):
         b.insert(0, Indexable(ord('A')))
         self.assertEqual(b, b'A')
 
+    def test_copied(self):
+        # Issue 4348.  Make sure that operations that don't mutate the array
+        # copy the bytes.
+        b = bytearray(b'abc')
+        #self.assertFalse(b is b.replace(b'abc', b'cde', 0))
+
+        t = bytearray([i for i in range(256)])
+        x = bytearray(b'')
+        self.assertFalse(x is x.translate(t))
+
     def test_partition_bytearray_doesnt_share_nullstring(self):
         a, b, c = bytearray(b"x").partition(b"y")
         self.assertEqual(b, b"")

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 2.7 alpha 1
 Core and Builtins
 -----------------
 
+- Issue #4348: Some bytearray methods returned that didn't cause any change to
+  the bytearray, returned the same bytearray instead of a copy.
+
 - Issue #4317: Fixed a crash in the imageop.rgb2rgb8() function.
 
 - Issue #4230: If ``__getattr__`` is a descriptor, it now functions correctly.

Objects/bytearrayobject.c

@@ -1423,7 +1423,7 @@ bytes_translate(PyByteArrayObject *self, PyObject *args)
 {
     register char *input, *output;
     register const char *table;
-    register Py_ssize_t i, c, changed = 0;
+    register Py_ssize_t i, c;
     PyObject *input_obj = (PyObject*)self;
     const char *output_start;
     Py_ssize_t inlen;
@@ -1469,14 +1469,8 @@ bytes_translate(PyByteArrayObject *self, PyObject *args)
         /* If no deletions are required, use faster code */
         for (i = inlen; --i >= 0; ) {
             c = Py_CHARMASK(*input++);
-            if (Py_CHARMASK((*output++ = table[c])) != c)
-                changed = 1;
+            *output++ = table[c];
         }
-        if (changed || !PyByteArray_CheckExact(input_obj))
-            goto done;
-        Py_DECREF(result);
-        Py_INCREF(input_obj);
-        result = input_obj;
         goto done;
     }
 
@@ -1491,13 +1485,6 @@ bytes_translate(PyByteArrayObject *self, PyObject *args)
         if (trans_table[c] != -1)
             if (Py_CHARMASK(*output++ = (char)trans_table[c]) == c)
                     continue;
-        changed = 1;
-    }
-    if (!changed && PyByteArray_CheckExact(input_obj)) {
-        Py_DECREF(result);
-        Py_INCREF(input_obj);
-        result = input_obj;
-        goto done;
     }
     /* Fix the size of the resulting string */
     if (inlen > 0)
@@ -1526,15 +1513,10 @@ done:
    !memcmp(target+offset+1, pattern+1, length-2) )
 
 
-/* Bytes ops must return a string.  */
-/* If the object is subclass of bytes, create a copy */
+/* Bytes ops must return a string, create a copy */
 Py_LOCAL(PyByteArrayObject *)
 return_self(PyByteArrayObject *self)
 {
-    if (PyByteArray_CheckExact(self)) {
-        Py_INCREF(self);
-        return (PyByteArrayObject *)self;
-    }
     return (PyByteArrayObject *)PyByteArray_FromStringAndSize(
             PyByteArray_AS_STRING(self),
             PyByteArray_GET_SIZE(self));