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gh-132108: Add Buffer Protocol support to int.from_bytes to improve performance #132109

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gh-132108: Add Buffer Protocol support to int.from_bytes to improve performance #132109

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d898d27
gh-132108: Add Buffer Protocol support to int.from_bytes
cmaloney Apr 5, 2025
b078ea1
Apply suggestions from code review
cmaloney Apr 7, 2025
e6ef5e1
Check bytes exact first to speed up that case
cmaloney Apr 9, 2025
9c511b1
Tweak comments, fix PEP-7 formatting
cmaloney Apr 22, 2025
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-04-04-20-38-29.gh-issue-132108.UwZIQy.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Speed up :meth:`int.from_bytes` when passed object supports :ref:`buffer
protocol <bufferobjects>`, like :class:`bytearray` by ~1.2x.
35 changes: 27 additions & 8 deletions Objects/longobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6439,6 +6439,7 @@ int_from_bytes_impl(PyTypeObject *type, PyObject *bytes_obj,
{
int little_endian;
PyObject *long_obj, *bytes;
Py_buffer view;

if (byteorder == NULL)
little_endian = 0;
Expand All @@ -6452,14 +6453,32 @@ int_from_bytes_impl(PyTypeObject *type, PyObject *bytes_obj,
return NULL;
}

bytes = PyObject_Bytes(bytes_obj);
if (bytes == NULL)
return NULL;

long_obj = _PyLong_FromByteArray(
(unsigned char *)PyBytes_AS_STRING(bytes), Py_SIZE(bytes),
little_endian, is_signed);
Py_DECREF(bytes);
/* Fast-path exact bytes. */
if (PyBytes_CheckExact(bytes_obj)) {
long_obj = _PyLong_FromByteArray(
(unsigned char *)PyBytes_AS_STRING(bytes_obj), Py_SIZE(bytes_obj),
little_endian, is_signed);
}
/* Use buffer protocol to avoid copies. */
else if (PyObject_CheckBuffer(bytes_obj)) {
if (PyObject_GetBuffer(bytes_obj, &view, PyBUF_SIMPLE) != 0) {
return NULL;
}
long_obj = _PyLong_FromByteArray(view.buf, view.len, little_endian,
is_signed);
PyBuffer_Release(&view);
}
else {
/* fallback: Construct a bytes then convert. */
bytes = PyObject_Bytes(bytes_obj);
if (bytes == NULL) {
return NULL;
}
long_obj = _PyLong_FromByteArray(
(unsigned char *)PyBytes_AS_STRING(bytes), Py_SIZE(bytes),
little_endian, is_signed);
Py_DECREF(bytes);
}

if (long_obj != NULL && type != &PyLong_Type) {
Py_SETREF(long_obj, PyObject_CallOneArg((PyObject *)type, long_obj));
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