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gh-129813, PEP 782: Add PyBytesWriter.overallocate (#138941)

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Disable overallocation in _PyBytes_FormatEx() at the last write.
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Victor Stinner 2025-09-15 23:15:32 +01:00 • committed by GitHub
parent 4554486f15
commit 4e00e2504f
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2 changed files with 21 additions and 9 deletions
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21
Objects/bytesobject.c
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@ -836,6 +836,11 @@ _PyBytes_FormatEx(const char *format, Py_ssize_t format_len,
if (v == NULL)
goto error;
if (fmtcnt == 0) {
/* last write: disable writer overallocation */
writer->overallocate = 0;
}
sign = 0;
fill = ' ';
switch (c) {
@ -1056,6 +1061,10 @@ _PyBytes_FormatEx(const char *format, Py_ssize_t format_len,
assert((res - before) == alloc);
#endif
} /* '%' */
/* If overallocation was disabled, ensure that it was the last
write. Otherwise, we missed an optimization */
assert(writer->overallocate || fmtcnt == 0 || use_bytearray);
} /* until end */
if (argidx < arglen && !dict) {
@ -3746,14 +3755,6 @@ _PyBytes_Repeat(char* dest, Py_ssize_t len_dest,
// --- PyBytesWriter API -----------------------------------------------------
struct PyBytesWriter {
char small_buffer[256];
PyObject *obj;
Py_ssize_t size;
int use_bytearray;
};
static inline char*
byteswriter_data(PyBytesWriter *writer)
{
@ -3802,7 +3803,8 @@ byteswriter_resize(PyBytesWriter *writer, Py_ssize_t size, int overallocate)
return 0;
}
if (overallocate && !writer->use_bytearray) {
overallocate &= writer->overallocate;
if (overallocate) {
if (size <= (PY_SSIZE_T_MAX - size / OVERALLOCATE_FACTOR)) {
size += size / OVERALLOCATE_FACTOR;
}
@ -3867,6 +3869,7 @@ byteswriter_create(Py_ssize_t size, int use_bytearray)
writer->obj = NULL;
writer->size = 0;
writer->use_bytearray = use_bytearray;
writer->overallocate = !use_bytearray;
if (size >= 1) {
if (byteswriter_resize(writer, size, 0) < 0) {