gh-155742: Use PyBytesWriter in bytes.translate() (#157346)

Replace soft deprecated _PyBytes_Resize() with PyBytesWriter.
Enhance test_bytes.test_translate().

Author: vstinner

Lib/test/test_bytes.py

@@ -1130,13 +1130,14 @@ def test_translate(self):
         self.assertRaises(ValueError, b.translate, bytes(range(255)))
 
         c = b.translate(rosetta, b'hello')
-        self.assertEqual(b, b'hello')
-        self.assertIsInstance(c, self.type2test)
+        self.assertEqual(c, b'')
+        self.assertEqual(type(c), self.type2test)
 
         c = b.translate(rosetta)
         d = b.translate(rosetta, b'')
-        self.assertEqual(c, d)
         self.assertEqual(c, b'helle')
+        self.assertEqual(type(c), self.type2test)
+        self.assertEqual(d, b'helle')
 
         c = b.translate(rosetta, b'l')
         self.assertEqual(c, b'hee')

Objects/bytesobject.c

@@ -2276,7 +2276,6 @@ bytes_translate_impl(PyBytesObject *self, PyObject *table,
     PyObject *input_obj = (PyObject*)self;
     const char *output_start, *del_table_chars=NULL;
     Py_ssize_t inlen, tablen, dellen = 0;
-    PyObject *result;
     int trans_table[256];
 
     if (PyBytes_Check(table)) {
@@ -2321,13 +2320,13 @@ bytes_translate_impl(PyBytesObject *self, PyObject *table,
     }
 
     inlen = PyBytes_GET_SIZE(input_obj);
-    result = PyBytes_FromStringAndSize((char *)NULL, inlen);
-    if (result == NULL) {
+    PyBytesWriter *writer = PyBytesWriter_Create(inlen);
+    if (writer == NULL) {
         PyBuffer_Release(&del_table_view);
         PyBuffer_Release(&table_view);
         return NULL;
     }
-    output_start = output = PyBytes_AS_STRING(result);
+    output_start = output = PyBytesWriter_GetData(writer);
     input = PyBytes_AS_STRING(input_obj);
 
     if (dellen == 0 && table_chars != NULL) {
@@ -2336,14 +2335,17 @@ bytes_translate_impl(PyBytesObject *self, PyObject *table,
             c = Py_CHARMASK(*input++);
             *output++ = table_chars[c];
         }
+        PyObject *result = PyBytesWriter_Finish(writer);
+
         /* Check if anything changed (for returning original object) */
         /* We save this check until the end so that the compiler will */
         /* unroll the loop above leading to MUCH faster code. */
-        if (PyBytes_CheckExact(input_obj)) {
+        if (result != NULL && PyBytes_CheckExact(input_obj)) {
             if (memcmp(PyBytes_AS_STRING(input_obj), output_start, inlen) == 0) {
                 Py_SETREF(result, Py_NewRef(input_obj));
             }
         }
+
         PyBuffer_Release(&del_table_view);
         PyBuffer_Release(&table_view);
         return result;
@@ -2370,13 +2372,11 @@ bytes_translate_impl(PyBytesObject *self, PyObject *table,
         changed = 1;
     }
     if (!changed && PyBytes_CheckExact(input_obj)) {
-        Py_DECREF(result);
+        PyBytesWriter_Discard(writer);
         return Py_NewRef(input_obj);
     }
     /* Fix the size of the resulting byte string */
-    if (inlen > 0)
-        _PyBytes_Resize(&result, output - output_start);
-    return result;
+    return PyBytesWriter_FinishWithPointer(writer, output);
 }