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gh-129813, PEP 782: Use PyBytesWriter in _io.FileIO.readall #138901

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Merged
merged 3 commits into from
Sep 15, 2025
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gh-129813, PEP 782: Use PyBytesWriter in _io.FileIO.readall #138901

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gh-129813, PEP 782: Use PyBytesWriter in _io.FileIO.readall
cmaloney Sep 15, 2025
b644ffb
Fix MSVC C2036 warning by casting to char to match what PyBytes_AS_ST…
cmaloney Sep 15, 2025
c6d5485
Remove News; no impact on end users
cmaloney Sep 15, 2025
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-09-14-18-21-17.gh-issue-129813.XN7EyU.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Update :class:`io.FileIO` to use :pep:`782` :c:type:`PyBytesWriter` to
implement :meth:`~io.RawIOBase.readall`
26 changes: 11 additions & 15 deletions Modules/_io/fileio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -739,7 +739,7 @@ _io_FileIO_readall_impl(fileio *self)
/*[clinic end generated code: output=faa0292b213b4022 input=10d8b2ec403302dc]*/
{
Py_off_t pos, end;
PyObject *result;
PyBytesWriter *writer;
Py_ssize_t bytes_read = 0;
Py_ssize_t n;
size_t bufsize;
Expand Down Expand Up @@ -794,10 +794,10 @@ _io_FileIO_readall_impl(fileio *self)
}
}


result = PyBytes_FromStringAndSize(NULL, bufsize);
if (result == NULL)
writer = PyBytesWriter_Create(bufsize);
if (writer == NULL) {
return NULL;
}

while (1) {
if (bytes_read >= (Py_ssize_t)bufsize) {
Expand All @@ -806,18 +806,18 @@ _io_FileIO_readall_impl(fileio *self)
PyErr_SetString(PyExc_OverflowError,
"unbounded read returned more bytes "
"than a Python bytes object can hold");
Py_DECREF(result);
PyBytesWriter_Discard(writer);
return NULL;
}

if (PyBytes_GET_SIZE(result) < (Py_ssize_t)bufsize) {
if (_PyBytes_Resize(&result, bufsize) < 0)
if (PyBytesWriter_GetSize(writer) < (Py_ssize_t)bufsize) {
if (PyBytesWriter_Resize(writer, bufsize) < 0)
return NULL;
}
}

n = _Py_read(self->fd,
PyBytes_AS_STRING(result) + bytes_read,
(char*)PyBytesWriter_GetData(writer) + bytes_read,
bufsize - bytes_read);

if (n == 0)
Expand All @@ -827,20 +827,16 @@ _io_FileIO_readall_impl(fileio *self)
PyErr_Clear();
if (bytes_read > 0)
break;
Py_DECREF(result);
PyBytesWriter_Discard(writer);
Py_RETURN_NONE;
}
Py_DECREF(result);
PyBytesWriter_Discard(writer);
return NULL;
}
bytes_read += n;
}

if (PyBytes_GET_SIZE(result) > bytes_read) {
if (_PyBytes_Resize(&result, bytes_read) < 0)
return NULL;
}
return result;
return PyBytesWriter_FinishWithSize(writer, bytes_read);
}

/*[clinic input]
Expand Down
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