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gh-129813, PEP 782: Use PyBytesWriter in bufferedio.c #138954

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Merged
merged 2 commits into from
Sep 15, 2025
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gh-129813, PEP 782: Use PyBytesWriter in bufferedio.c #138954

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gh-129813, PEP 782: Use PyBytesWriter in bufferedio.c
vstinner Sep 15, 2025
dd3f975
Address cmaloney's review
vstinner Sep 15, 2025
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44 changes: 23 additions & 21 deletions Modules/_io/bufferedio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1026,58 +1026,60 @@ static PyObject *
_io__Buffered_read1_impl(buffered *self, Py_ssize_t n)
/*[clinic end generated code: output=bcc4fb4e54d103a3 input=3d0ad241aa52b36c]*/
{
Py_ssize_t have, r;
PyObject *res = NULL;

CHECK_INITIALIZED(self)
if (n < 0) {
n = self->buffer_size;
}

CHECK_CLOSED(self, "read of closed file")

if (n == 0)
return PyBytes_FromStringAndSize(NULL, 0);
if (n == 0) {
return Py_GetConstant(Py_CONSTANT_EMPTY_BYTES);
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@cmaloney cmaloney Sep 15, 2025

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This comes up fairly frequently in the I/O code, thinking of making a _Py_EMPTY_BYTES internal macro for it (separate from this PR)

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@vstinner vstinner Sep 15, 2025

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Do you mean a macro specific to the _io module?

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@cmaloney cmaloney Sep 15, 2025

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I was thinking pycore_bytesobject.h; currently shows up 24 times across the CPython source code. BufferedIO and a couple other places also use a pattern: (PyObject *)&_Py_SINGLETON(bytes_empty)

}

/* Return up to n bytes. If at least one byte is buffered, we
only return buffered bytes. Otherwise, we do one raw read. */

have = Py_SAFE_DOWNCAST(READAHEAD(self), Py_off_t, Py_ssize_t);
Py_ssize_t have = Py_SAFE_DOWNCAST(READAHEAD(self), Py_off_t, Py_ssize_t);
if (have > 0) {
n = Py_MIN(have, n);
res = _bufferedreader_read_fast(self, n);
PyObject *res = _bufferedreader_read_fast(self, n);
assert(res != Py_None);
return res;
}
res = PyBytes_FromStringAndSize(NULL, n);
if (res == NULL)
return NULL;

if (!ENTER_BUFFERED(self)) {
Py_DECREF(res);
return NULL;
}

/* Flush the write buffer if necessary */
if (self->writable) {
PyObject *r = buffered_flush_and_rewind_unlocked(self);
if (r == NULL) {
PyObject *res = buffered_flush_and_rewind_unlocked(self);
if (res == NULL) {
LEAVE_BUFFERED(self)
Py_DECREF(res);
return NULL;
}
Py_DECREF(r);
Py_DECREF(res);
}
_bufferedreader_reset_buf(self);
r = _bufferedreader_raw_read(self, PyBytes_AS_STRING(res), n);

PyBytesWriter *writer = PyBytesWriter_Create(n);
if (writer == NULL) {
return NULL;
}

Py_ssize_t r = _bufferedreader_raw_read(self,
PyBytesWriter_GetData(writer), n);
LEAVE_BUFFERED(self)
if (r == -1) {
Py_DECREF(res);
PyBytesWriter_Discard(writer);
return NULL;
}
if (r == -2)
if (r == -2) {
r = 0;
if (n > r)
_PyBytes_Resize(&res, r);
return res;
}

return PyBytesWriter_FinishWithSize(writer, r);
}

static PyObject *
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