gh-128213: fast path for bytes creation from list and tuple

Misc/NEWS.d/next/Core_and_Builtins/2024-12-24-08-44-49.gh-issue-128213.Y71jDi.rst

@@ -0,0 +1,3 @@
+Speed up :class:`bytes` creation from :class:`list` and :class:`tuple` of integers. Benchmarks show that from a list with 1000000 random numbers the time to create a bytes object is reduced by around 31%, or 30% with 10000 numbers, or 27% with 100 numbers.
+
+Patch by Ben Hsing

Objects/bytesobject.c

@@ -6,6 +6,7 @@
 #include "pycore_bytesobject.h" // _PyBytes_Find(), _PyBytes_Repeat()
 #include "pycore_call.h" // _PyObject_CallNoArgs()
 #include "pycore_ceval.h" // _PyEval_GetBuiltin()
+#include "pycore_critical_section.h" // Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST()
 #include "pycore_format.h" // F_LJUST
 #include "pycore_global_objects.h"// _Py_GET_GLOBAL_OBJECT()
 #include "pycore_initconfig.h" // _PyStatus_OK()
@@ -2810,82 +2811,46 @@ _PyBytes_FromBuffer(PyObject *x)
 }
 
 static PyObject*
-_PyBytes_FromList(PyObject *x)
+_PyBytes_FromSequence(PyObject *x)
 {
- Py_ssize_t i, size = PyList_GET_SIZE(x);
- Py_ssize_t value;
- char *str;
- PyObject *item;
- _PyBytesWriter writer;
-
- _PyBytesWriter_Init(&writer);
- str = _PyBytesWriter_Alloc(&writer, size);
- if (str == NULL)
+ Py_ssize_t size = PySequence_Fast_GET_SIZE(x);
+ PyObject *bytes = _PyBytes_FromSize(size, 0);
+ if (bytes == NULL) {
  return NULL;
- writer.overallocate = 1;
- size = writer.allocated;
-
- for (i = 0; i < PyList_GET_SIZE(x); i++) {
- item = PyList_GET_ITEM(x, i);
- Py_INCREF(item);
- value = PyNumber_AsSsize_t(item, NULL);
- Py_DECREF(item);
- if (value == -1 && PyErr_Occurred())
- goto error;
-
- if (value < 0 || value >= 256) {
- PyErr_SetString(PyExc_ValueError,
- "bytes must be in range(0, 256)");
- goto error;
- }
-
- if (i >= size) {
- str = _PyBytesWriter_Resize(&writer, str, size+1);
- if (str == NULL)
- return NULL;
- size = writer.allocated;
- }
- *str++ = (char) value;
  }
- return _PyBytesWriter_Finish(&writer, str);
-
- error:
- _PyBytesWriter_Dealloc(&writer);
- return NULL;
-}
-
-static PyObject*
-_PyBytes_FromTuple(PyObject *x)
-{
- PyObject *bytes;
- Py_ssize_t i, size = PyTuple_GET_SIZE(x);
- Py_ssize_t value;
- char *str;
- PyObject *item;
-
- bytes = PyBytes_FromStringAndSize(NULL, size);
- if (bytes == NULL)
- return NULL;
- str = ((PyBytesObject *)bytes)->ob_sval;
-
- for (i = 0; i < size; i++) {
- item = PyTuple_GET_ITEM(x, i);
- value = PyNumber_AsSsize_t(item, NULL);
- if (value == -1 && PyErr_Occurred())
+ char *str = PyBytes_AS_STRING(bytes);
+ PyObject *const *items = PySequence_Fast_ITEMS(x);
+ Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(x);
+ for (Py_ssize_t i = 0; i < size; i++) {
+ if (!PyLong_Check(items[i])) {
+ Py_DECREF(bytes);
+ /* Py_None as a fallback sentinel to the slow path */
+ bytes = Py_None;
+ goto done;
+ }
+ Py_ssize_t value = PyNumber_AsSsize_t(items[i], NULL);
+ if (value == -1 && PyErr_Occurred()) {
  goto error;
-
+ }
  if (value < 0 || value >= 256) {
  PyErr_SetString(PyExc_ValueError,
  "bytes must be in range(0, 256)");
  goto error;
  }
  *str++ = (char) value;
  }
- return bytes;
-
+ goto done;
  error:
  Py_DECREF(bytes);
- return NULL;
+ bytes = NULL;
+ done:
+ /* some C parsers require a label not to be at the end of a compound
+ statement, which the ending macro of a critical section introduces, so
+ we need an empty statement here to satisfy that syntax rule */
+ ;
+ /* both success and failure need to end the critical section */
+ Py_END_CRITICAL_SECTION_SEQUENCE_FAST();
+ return bytes;
 }
 
 static PyObject *
@@ -2968,11 +2933,13 @@ PyBytes_FromObject(PyObject *x)
  if (PyObject_CheckBuffer(x))
  return _PyBytes_FromBuffer(x);
 
- if (PyList_CheckExact(x))
- return _PyBytes_FromList(x);
-
- if (PyTuple_CheckExact(x))
- return _PyBytes_FromTuple(x);
+ if (PyList_CheckExact(x) || PyTuple_CheckExact(x)) {
+ PyObject *bytes = _PyBytes_FromSequence(x);
+ /* Py_None as a fallback sentinel to the slow path */
+ if (bytes != Py_None) {
+ return bytes;
+ }
+ }
 
  if (!PyUnicode_Check(x)) {
  it = PyObject_GetIter(x);