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gh-139852: Add PyObject_GetDict() function by vstinner · Pull Request #139968 · python/cpython · GitHub

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41 changes: 36 additions & 5 deletions Doc/c-api/object.rst
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
Original file line number Diff line number Diff line change
Expand Up @@ -268,14 +268,19 @@ Object Protocol
A generic implementation for the getter of a ``__dict__`` descriptor. It
creates the dictionary if necessary.

This function may also be called to get the :py:attr:`~object.__dict__`
of the object *o*. Pass ``NULL`` for *context* when calling it.
Since this function may need to allocate memory for the
dictionary, it may be more efficient to call :c:func:`PyObject_GetAttr`
when accessing an attribute on the object.
Raise an :exc:`AttributeError` if the object has no ``__dict__``.

On failure, returns ``NULL`` with an exception set.

To get the ``__dict__`` of an arbitrary object (that is, when you are not
implementing a getter of a ``__dict__`` descriptor), prefer using
:c:func:`PyObject_GetDict` instead.
Alternately, use this function and pass ``NULL`` for *context*.

Since this function may need to allocate memory for the
dictionary, it may be more efficient to call :c:func:`PyObject_GetAttr`
when accessing a single attribute on the object.

.. versionadded:: 3.3


Expand All @@ -287,6 +292,27 @@ Object Protocol
.. versionadded:: 3.3


.. c:function:: int PyObject_GetDict(PyObject *obj, PyObject **dict)
Comment thread
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Get a pointer to :py:attr:`~object.__dict__` of the object *obj*.

* If there is a ``__dict__``, set *\*dict* to a :term:`strong reference`
to the dictionary and return ``1``.
* If there is no ``__dict__``, set *\*dict* to ``NULL`` without setting
an exception and return ``0``.
* On error, set an exception and return ``-1``.

This function may need to allocate memory for the dictionary, so it may be
more efficient to call :c:func:`PyObject_GetAttr` when accessing an
attribute on the object.

.. versionadded:: next

.. seealso::
:c:func:`PyObject_GenericGetDict` and :c:func:`PyObject_GenericSetDict`
functions.


.. c:function:: PyObject** _PyObject_GetDictPtr(PyObject *obj)

Return a pointer to :py:attr:`~object.__dict__` of the object *obj*.
Expand All @@ -296,6 +322,11 @@ Object Protocol
dictionary, so it may be more efficient to call :c:func:`PyObject_GetAttr`
when accessing an attribute on the object.

.. deprecated:: 3.15
Use :c:func:`PyObject_GetDict`, :c:func:`PyObject_GetAttr`,
:c:func:`PyObject_SetAttr` or :c:func:`PyObject_ClearManagedDict`
instead.


.. c:function:: PyObject* PyObject_RichCompare(PyObject *o1, PyObject *o2, int opid)

Expand Down
8 changes: 8 additions & 0 deletions Doc/whatsnew/3.15.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -884,6 +884,10 @@ New features

(Contributed by Victor Stinner in :gh:`129813`.)

* Add :c:type:`PyObject_GetDict` function to get the
:py:attr:`~object.__dict__` of an object.
(Contributed by Victor Stinner in :gh:`139852`.)

* Add :c:func:`PyTuple_FromArray` to create a :class:`tuple` from an array.
(Contributed by Victor Stinner in :gh:`111489`.)

Expand Down Expand Up @@ -1017,6 +1021,10 @@ Deprecated C APIs
since 3.15 and will be removed in 3.17.
(Contributed by Nikita Sobolev in :gh:`136355`.)

* Deprecate the private :c:func:`_PyObject_GetDictPtr` function:
use public :c:func:`PyObject_GetDict`, :c:func:`PyObject_GetAttr`,
:c:func:`PyObject_SetAttr` or :c:func:`PyObject_ClearManagedDict` instead.
(Contributed by Victor Stinner in :gh:`139852`.)

.. Add C API deprecations above alphabetically, not here at the end.

Expand Down
3 changes: 2 additions & 1 deletion Include/cpython/object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -299,7 +299,8 @@ PyAPI_FUNC(void) _PyObject_Dump(PyObject *);

PyAPI_FUNC(PyObject*) _PyObject_GetAttrId(PyObject *, _Py_Identifier *);

PyAPI_FUNC(PyObject **) _PyObject_GetDictPtr(PyObject *);
PyAPI_FUNC(int) PyObject_GetDict(PyObject *obj, PyObject **dict);
Py_DEPRECATED(3.15) PyAPI_FUNC(PyObject **) _PyObject_GetDictPtr(PyObject *);
PyAPI_FUNC(void) PyObject_CallFinalizer(PyObject *);
PyAPI_FUNC(int) PyObject_CallFinalizerFromDealloc(PyObject *);

Expand Down
47 changes: 47 additions & 0 deletions Lib/test/test_capi/test_object.py
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Original file line number Diff line number Diff line change
Expand Up @@ -247,5 +247,52 @@ def func(x):

func(object())

def test_object_getdict(self):
# Test PyObject_GetDict()
object_getdict = _testcapi.object_getdict

class MyClass:
pass
obj = MyClass()

dict1 = object_getdict(obj)
dict2 = obj.__dict__
self.assertIs(dict1, dict2)

obj.attr = 123
self.assertEqual(dict1, {'attr': 123})

class NoDict:
__slots__ = ()
obj = NoDict()

self.assertEqual(object_getdict(obj), AttributeError)

# CRASHES object_getdict(NULL)

def test_object_genericgetdict(self):
# Test PyObject_GenericGetDict()
object_genericgetdict = _testcapi.object_genericgetdict

class MyClass:
pass
obj = MyClass()
obj.attr = 123

dict1 = object_genericgetdict(obj)
dict2 = obj.__dict__
self.assertIs(dict1, dict2)

class NoDict:
__slots__ = ()
obj = NoDict()

with self.assertRaisesRegex(AttributeError,
"This object has no __dict__"):
object_genericgetdict(obj)

# CRASHES object_genericgetdict(NULL)


if __name__ == "__main__":
unittest.main()
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Add :c:type:`PyObject_GetDict` function to get the :py:attr:`~object.__dict__`
of an object. Patch by Victor Stinner.
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Deprecate the private :c:func:`_PyObject_GetDictPtr` function: use public
:c:func:`PyObject_GetDict`, :c:func:`PyObject_GetAttr`,
:c:func:`PyObject_SetAttr` or :c:func:`PyObject_ClearManagedDict` instead.
41 changes: 41 additions & 0 deletions Modules/_testcapi/object.c
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Original file line number Diff line number Diff line change
Expand Up @@ -485,6 +485,45 @@ is_uniquely_referenced(PyObject *self, PyObject *op)
}


static PyObject *
object_getdict(PyObject *self, PyObject *obj)
{
NULLABLE(obj);

PyObject *dict = UNINITIALIZED_PTR;
switch (PyObject_GetDict(obj, &dict)) {
case -1:
assert(dict == NULL);
return NULL;
case 0:
assert(dict == NULL);
return Py_NewRef(PyExc_AttributeError);
case 1:
return dict;
default:
Py_FatalError("PyObject_GetDict() returned invalid code");
Py_UNREACHABLE();
}
}


static PyObject *
object_genericgetdict(PyObject *self, PyObject *obj)
{
NULLABLE(obj);

PyObject *dict = PyObject_GenericGetDict(obj, NULL);
if (dict != NULL) {
return dict;
}

if (PyErr_Occurred()) {
return NULL;
}
return Py_NewRef(PyExc_AttributeError);
}


static PyMethodDef test_methods[] = {
{"call_pyobject_print", call_pyobject_print, METH_VARARGS},
{"pyobject_print_null", pyobject_print_null, METH_VARARGS},
Expand All @@ -511,6 +550,8 @@ static PyMethodDef test_methods[] = {
{"test_py_is_funcs", test_py_is_funcs, METH_NOARGS},
{"clear_managed_dict", clear_managed_dict, METH_O, NULL},
{"is_uniquely_referenced", is_uniquely_referenced, METH_O},
{"object_getdict", object_getdict, METH_O},
{"object_genericgetdict", object_genericgetdict, METH_O},
{NULL},
};

Expand Down
53 changes: 43 additions & 10 deletions Objects/object.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1540,6 +1540,28 @@ _PyObject_ComputedDictPointer(PyObject *obj)
return (PyObject **) ((char *)obj + dictoffset);
}

static int
object_getdictptr(PyObject *obj, PyObject ***dict_ptr)
{
if ((Py_TYPE(obj)->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0) {
*dict_ptr = _PyObject_ComputedDictPointer(obj);
return (*dict_ptr != NULL);
}

PyDictObject *dict = _PyObject_GetManagedDict(obj);
if (dict == NULL && Py_TYPE(obj)->tp_flags & Py_TPFLAGS_INLINE_VALUES) {
dict = _PyObject_MaterializeManagedDict(obj);
if (dict == NULL) {
*dict_ptr = NULL;
return -1;
}
}
*dict_ptr = (PyObject **)&_PyObject_ManagedDictPointer(obj)->dict;
assert(*dict_ptr != NULL);
return 1;
}


/* Helper to get a pointer to an object's __dict__ slot, if any.
* Creates the dict from inline attributes if necessary.
* Does not set an exception.
Expand All @@ -1550,20 +1572,31 @@ _PyObject_ComputedDictPointer(PyObject *obj)
PyObject **
_PyObject_GetDictPtr(PyObject *obj)
{
if ((Py_TYPE(obj)->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0) {
return _PyObject_ComputedDictPointer(obj);
PyObject **dict_ptr;
if (object_getdictptr(obj, &dict_ptr) < 0) {
PyErr_Clear();
}
PyDictObject *dict = _PyObject_GetManagedDict(obj);
if (dict == NULL && Py_TYPE(obj)->tp_flags & Py_TPFLAGS_INLINE_VALUES) {
dict = _PyObject_MaterializeManagedDict(obj);
if (dict == NULL) {
PyErr_Clear();
return NULL;
}
return dict_ptr;
}


int
PyObject_GetDict(PyObject *obj, PyObject **dict)
{
PyObject **dict_ptr;
int res = object_getdictptr(obj, &dict_ptr);
if (res == 1) {
assert(*dict_ptr != NULL);
*dict = Py_NewRef(*dict_ptr);
}
return (PyObject **)&_PyObject_ManagedDictPointer(obj)->dict;
else {
assert(dict_ptr == NULL);
*dict = NULL;
}
return res;
}


PyObject *
PyObject_SelfIter(PyObject *obj)
{
Expand Down
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