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bpo-32571: Avoid raising unneeded AttributeError and silencing it C code. #5205

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bpo-32571: Avoid raising unneeded AttributeError and silencing it C code. #5205

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1 change: 1 addition & 0 deletions Include/object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -539,6 +539,7 @@ PyAPI_FUNC(int) _PyObject_IsAbstract(PyObject *);
/* Same as PyObject_GetAttr(), but don't raise AttributeError. */
PyAPI_FUNC(PyObject *) _PyObject_GetAttrWithoutError(PyObject *, PyObject *);
PyAPI_FUNC(PyObject *) _PyObject_GetAttrId(PyObject *, struct _Py_Identifier *);
PyAPI_FUNC(PyObject *) _PyObject_GetAttrIdWithoutError(PyObject *, struct _Py_Identifier *);
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@1st1 1st1 Jan 16, 2018 •
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Can we have an int return value so that we don't need to call PyErr_Occurred()? IMHO, it's an API anti-pattern to require double checking what NULL means.

PyAPI_FUNC(int) _PyObject_GetAttrIdWithoutError(
    PyObject *, struct _Py_Identifier *, PyObject **);
  • -1 error
  • 0 not found
  • 1 found

I'd also do this for _PyObject_GetAttrWithoutError which we committed today. /cc @methane

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Make sense. Go ahead.

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For usability, third argument should be filled with NULL when returning 1.
By it, caller can use if (val == NULL) instead of assigning return value to local variable.

if (_PyObject_GetAttrIdWithoutError((PyObject *)deque, &PyId___dict__, &func) < 0) {
    // when error happens
    return NULL;
}
if (func == NULL) {
    // when `__dict__` not found.
    Py_RETURN_NONE;
}

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Yeah, I agree, it's even better.

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Then I think It would be better to rename the function to _PyObject_LookupAttrId or _PyObject_FindAttrId. _PyObject_GetAttrIdWithoutError looks misleading bacause despite its name it can raise an error.

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I agree. "find" is far better than "without error".

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I like LookupAttrId. It sounds better.

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@1st1 1st1 Jan 17, 2018 •
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BTW, I'd also remove the leading underscore from _PyObject_GetAttrWithoutError, making it PyObject_LookupAttr (and we keep the underscore for _PyObject_LookupAttrId).

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Hm, "lookup" make sense too because there are _PyType_Lookup and _PyType_LookupId
and they doesn't set exception.
And +1 to make it public API.

PyAPI_FUNC(int) _PyObject_SetAttrId(PyObject *, struct _Py_Identifier *, PyObject *);
PyAPI_FUNC(int) _PyObject_HasAttrId(PyObject *, struct _Py_Identifier *);
PyAPI_FUNC(PyObject **) _PyObject_GetDictPtr(PyObject *);
Expand Down
5 changes: 2 additions & 3 deletions Modules/_collectionsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1339,12 +1339,11 @@ deque_reduce(dequeobject *deque)
PyObject *dict, *it;
_Py_IDENTIFIER(__dict__);

dict = _PyObject_GetAttrId((PyObject *)deque, &PyId___dict__);
dict = _PyObject_GetAttrIdWithoutError((PyObject *)deque, &PyId___dict__);
if (dict == NULL) {
if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
if (PyErr_Occurred()) {
return NULL;
}
PyErr_Clear();
dict = Py_None;
Py_INCREF(dict);
}
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6 changes: 2 additions & 4 deletions Modules/_io/fileio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1073,11 +1073,9 @@ fileio_repr(fileio *self)
if (self->fd < 0)
return PyUnicode_FromFormat("<_io.FileIO [closed]>");

nameobj = _PyObject_GetAttrId((PyObject *) self, &PyId_name);
nameobj = _PyObject_GetAttrIdWithoutError((PyObject *) self, &PyId_name);
if (nameobj == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError))
PyErr_Clear();
else
if (PyErr_Occurred())
return NULL;
res = PyUnicode_FromFormat(
"<_io.FileIO fd=%d mode='%s' closefd=%s>",
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5 changes: 2 additions & 3 deletions Modules/_io/iobase.c
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Original file line number Diff line number Diff line change
Expand Up @@ -135,12 +135,11 @@ iobase_is_closed(PyObject *self)
PyObject *res;
/* This gets the derived attribute, which is *not* __IOBase_closed
in most cases! */
res = _PyObject_GetAttrId(self, &PyId___IOBase_closed);
res = _PyObject_GetAttrIdWithoutError(self, &PyId___IOBase_closed);
if (res == NULL) {
if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
if (PyErr_Occurred()) {
return -1;
}
PyErr_Clear();
return 0;
}
Py_DECREF(res);
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12 changes: 4 additions & 8 deletions Modules/_io/textio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -924,11 +924,9 @@ _textiowrapper_set_encoder(textio *self, PyObject *codec_info,
return -1;

/* Get the normalized named of the codec */
res = _PyObject_GetAttrId(codec_info, &PyId_name);
res = _PyObject_GetAttrIdWithoutError(codec_info, &PyId_name);
if (res == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError))
PyErr_Clear();
else
if (PyErr_Occurred())
return -1;
}
else if (PyUnicode_Check(res)) {
Expand Down Expand Up @@ -1178,12 +1176,10 @@ _io_TextIOWrapper___init___impl(textio *self, PyObject *buffer,
if (Py_TYPE(buffer) == &PyBufferedReader_Type ||
Py_TYPE(buffer) == &PyBufferedWriter_Type ||
Py_TYPE(buffer) == &PyBufferedRandom_Type) {
raw = _PyObject_GetAttrId(buffer, &PyId_raw);
raw = _PyObject_GetAttrIdWithoutError(buffer, &PyId_raw);
/* Cache the raw FileIO object to speed up 'closed' checks */
if (raw == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError))
PyErr_Clear();
else
if (PyErr_Occurred())
goto error;
}
else if (Py_TYPE(raw) == &PyFileIO_Type)
Expand Down
108 changes: 39 additions & 69 deletions Modules/_pickle.c
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Original file line number Diff line number Diff line change
Expand Up @@ -370,14 +370,13 @@ init_method_ref(PyObject *self, _Py_Identifier *name,

/* *method_func and *method_self should be consistent. All refcount decrements
should be occurred after setting *method_self and *method_func. */
func = _PyObject_GetAttrId(self, name);
func = _PyObject_GetAttrIdWithoutError(self, name);
if (func == NULL) {
*method_self = NULL;
Py_CLEAR(*method_func);
if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
if (PyErr_Occurred()) {
return -1;
}
PyErr_Clear();
return 0;
}

Expand Down Expand Up @@ -1155,11 +1154,12 @@ _Pickler_SetOutputStream(PicklerObject *self, PyObject *file)
{
_Py_IDENTIFIER(write);
assert(file != NULL);
self->write = _PyObject_GetAttrId(file, &PyId_write);
self->write = _PyObject_GetAttrIdWithoutError(file, &PyId_write);
if (self->write == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError))
if (!PyErr_Occurred()) {
PyErr_SetString(PyExc_TypeError,
"file must have a 'write' attribute");
}
return -1;
}

Expand Down Expand Up @@ -1504,19 +1504,17 @@ _Unpickler_SetInputStream(UnpicklerObject *self, PyObject *file)
_Py_IDENTIFIER(read);
_Py_IDENTIFIER(readline);

self->peek = _PyObject_GetAttrId(file, &PyId_peek);
if (self->peek == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError))
PyErr_Clear();
else
return -1;
self->peek = _PyObject_GetAttrIdWithoutError(file, &PyId_peek);
if (self->peek == NULL && PyErr_Occurred()) {
return -1;
}
self->read = _PyObject_GetAttrId(file, &PyId_read);
self->readline = _PyObject_GetAttrId(file, &PyId_readline);
self->read = _PyObject_GetAttrIdWithoutError(file, &PyId_read);
self->readline = _PyObject_GetAttrIdWithoutError(file, &PyId_readline);
if (self->readline == NULL || self->read == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError))
if (!PyErr_Occurred()) {
PyErr_SetString(PyExc_TypeError,
"file must have 'read' and 'readline' attributes");
}
Py_CLEAR(self->read);
Py_CLEAR(self->readline);
Py_CLEAR(self->peek);
Expand Down Expand Up @@ -1691,7 +1689,7 @@ get_deep_attribute(PyObject *obj, PyObject *names, PyObject **pparent)
PyObject *name = PyList_GET_ITEM(names, i);
Py_XDECREF(parent);
parent = obj;
obj = PyObject_GetAttr(parent, name);
obj = _PyObject_GetAttrWithoutError(parent, name);
if (obj == NULL) {
Py_DECREF(parent);
return NULL;
Expand All @@ -1704,16 +1702,6 @@ get_deep_attribute(PyObject *obj, PyObject *names, PyObject **pparent)
return obj;
}

static void
reformat_attribute_error(PyObject *obj, PyObject *name)
{
if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
PyErr_Clear();
PyErr_Format(PyExc_AttributeError,
"Can't get attribute %R on %R", name, obj);
}
}


static PyObject *
getattribute(PyObject *obj, PyObject *name, int allow_qualname)
Expand All @@ -1728,9 +1716,11 @@ getattribute(PyObject *obj, PyObject *name, int allow_qualname)
Py_DECREF(dotted_path);
}
else
attr = PyObject_GetAttr(obj, name);
if (attr == NULL)
reformat_attribute_error(obj, name);
attr = _PyObject_GetAttrWithoutError(obj, name);
if (attr == NULL && !PyErr_Occurred()) {
PyErr_Format(PyExc_AttributeError,
"Can't get attribute %R on %R", name, obj);
}
return attr;
}

Expand All @@ -1748,9 +1738,6 @@ _checkmodule(PyObject *module_name, PyObject *module,

PyObject *candidate = get_deep_attribute(module, dotted_path, NULL);
if (candidate == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
PyErr_Clear();
}
return -1;
}
if (candidate != global) {
Expand All @@ -1772,12 +1759,11 @@ whichmodule(PyObject *global, PyObject *dotted_path)
_Py_IDENTIFIER(modules);
_Py_IDENTIFIER(__main__);

module_name = _PyObject_GetAttrId(global, &PyId___module__);
module_name = _PyObject_GetAttrIdWithoutError(global, &PyId___module__);

if (module_name == NULL) {
if (!PyErr_ExceptionMatches(PyExc_AttributeError))
if (PyErr_Occurred())
return NULL;
PyErr_Clear();
}
else {
/* In some rare cases (e.g., bound methods of extension types),
Expand Down Expand Up @@ -3328,13 +3314,10 @@ save_global(PicklerObject *self, PyObject *obj, PyObject *name)
global_name = name;
}
else {
global_name = _PyObject_GetAttrId(obj, &PyId___qualname__);
global_name = _PyObject_GetAttrIdWithoutError(obj, &PyId___qualname__);
if (global_name == NULL) {
if (!PyErr_ExceptionMatches(PyExc_AttributeError))
if (PyErr_Occurred())
goto error;
PyErr_Clear();
}
if (global_name == NULL) {
global_name = _PyObject_GetAttrId(obj, &PyId___name__);
if (global_name == NULL)
goto error;
Expand Down Expand Up @@ -3656,13 +3639,10 @@ get_class(PyObject *obj)
PyObject *cls;
_Py_IDENTIFIER(__class__);

cls = _PyObject_GetAttrId(obj, &PyId___class__);
if (cls == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
PyErr_Clear();
cls = (PyObject *) Py_TYPE(obj);
Py_INCREF(cls);
}
cls = _PyObject_GetAttrIdWithoutError(obj, &PyId___class__);
if (cls == NULL && !PyErr_Occurred()) {
cls = (PyObject *) Py_TYPE(obj);
Py_INCREF(cls);
}
return cls;
}
Expand Down Expand Up @@ -3734,12 +3714,11 @@ save_reduce(PicklerObject *self, PyObject *args, PyObject *obj)
PyObject *name;
_Py_IDENTIFIER(__name__);

name = _PyObject_GetAttrId(callable, &PyId___name__);
name = _PyObject_GetAttrIdWithoutError(callable, &PyId___name__);
if (name == NULL) {
if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
if (PyErr_Occurred()) {
return -1;
}
PyErr_Clear();
}
else if (PyUnicode_Check(name)) {
_Py_IDENTIFIER(__newobj_ex__);
Expand Down Expand Up @@ -4108,23 +4087,20 @@ save(PicklerObject *self, PyObject *obj, int pers_save)
don't actually have to check for a __reduce__ method. */

/* Check for a __reduce_ex__ method. */
reduce_func = _PyObject_GetAttrId(obj, &PyId___reduce_ex__);
reduce_func = _PyObject_GetAttrIdWithoutError(obj, &PyId___reduce_ex__);
if (reduce_func != NULL) {
PyObject *proto;
proto = PyLong_FromLong(self->proto);
if (proto != NULL) {
reduce_value = _Pickle_FastCall(reduce_func, proto);
}
}
else if (PyErr_Occurred()) {
goto error;
}
else {
PickleState *st = _Pickle_GetGlobalState();

if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
PyErr_Clear();
}
else {
goto error;
}
/* Check for a __reduce__ method. */
reduce_func = _PyObject_GetAttrId(obj, &PyId___reduce__);
if (reduce_func != NULL) {
Expand Down Expand Up @@ -4401,13 +4377,10 @@ _pickle_Pickler___init___impl(PicklerObject *self, PyObject *file,
return -1;
}

self->dispatch_table = _PyObject_GetAttrId((PyObject *)self,
self->dispatch_table = _PyObject_GetAttrIdWithoutError((PyObject *)self,
&PyId_dispatch_table);
if (self->dispatch_table == NULL) {
if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
return -1;
}
PyErr_Clear();
if (self->dispatch_table == NULL && PyErr_Occurred()) {
return -1;
}

return 0;
Expand Down Expand Up @@ -5370,12 +5343,11 @@ instantiate(PyObject *cls, PyObject *args)
if (!PyTuple_GET_SIZE(args) && PyType_Check(cls)) {
_Py_IDENTIFIER(__getinitargs__);
_Py_IDENTIFIER(__new__);
PyObject *func = _PyObject_GetAttrId(cls, &PyId___getinitargs__);
PyObject *func = _PyObject_GetAttrIdWithoutError(cls, &PyId___getinitargs__);
if (func == NULL) {
if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
if (PyErr_Occurred()) {
return NULL;
}
PyErr_Clear();
return _PyObject_CallMethodIdObjArgs(cls, &PyId___new__, cls, NULL);
}
Py_DECREF(func);
Expand Down Expand Up @@ -6225,11 +6197,9 @@ load_build(UnpicklerObject *self)

inst = self->stack->data[Py_SIZE(self->stack) - 1];

setstate = _PyObject_GetAttrId(inst, &PyId___setstate__);
setstate = _PyObject_GetAttrIdWithoutError(inst, &PyId___setstate__);
if (setstate == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError))
PyErr_Clear();
else {
if (PyErr_Occurred()) {
Py_DECREF(state);
return -1;
}
Expand Down
5 changes: 2 additions & 3 deletions Modules/arraymodule.c
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Expand Up @@ -2203,11 +2203,10 @@ array_array___reduce_ex__(arrayobject *self, PyObject *value)
if (protocol == -1 && PyErr_Occurred())
return NULL;

dict = _PyObject_GetAttrId((PyObject *)self, &PyId___dict__);
dict = _PyObject_GetAttrIdWithoutError((PyObject *)self, &PyId___dict__);
if (dict == NULL) {
if (!PyErr_ExceptionMatches(PyExc_AttributeError))
if (PyErr_Occurred())
return NULL;
PyErr_Clear();
dict = Py_None;
Py_INCREF(dict);
}
Expand Down
5 changes: 2 additions & 3 deletions Modules/itertoolsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -830,17 +830,16 @@ tee(PyObject *self, PyObject *args)
return NULL;
}

copyfunc = _PyObject_GetAttrId(it, &PyId___copy__);
copyfunc = _PyObject_GetAttrIdWithoutError(it, &PyId___copy__);
if (copyfunc != NULL) {
copyable = it;
}
else if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
else if (PyErr_Occurred()) {
Py_DECREF(it);
Py_DECREF(result);
return NULL;
}
else {
PyErr_Clear();
copyable = tee_fromiterable(it);
Py_DECREF(it);
if (copyable == NULL) {
Expand Down
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