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bpo-1635741: Add PyModule_AddObjectRef() function (GH-23122)
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Added PyModule_AddObjectRef() function: similar to
PyModule_AddObjectRef() but don't steal a reference to the value on
success.
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vstinner authored Nov 4, 2020
1 parent 3529718 commit 8021875
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Showing 5 changed files with 146 additions and 46 deletions.
104 changes: 90 additions & 14 deletions Doc/c-api/module.rst
Original file line number Diff line number Diff line change
Expand Up @@ -264,7 +264,7 @@ of the following two module creation functions:
instead; only use this if you are sure you need it.
Before it is returned from in the initialization function, the resulting module
object is typically populated using functions like :c:func:`PyModule_AddObject`.
object is typically populated using functions like :c:func:`PyModule_AddObjectRef`.
.. _multi-phase-initialization:
Expand Down Expand Up @@ -437,26 +437,102 @@ a function called from a module execution slot (if using multi-phase
initialization), can use the following functions to help initialize the module
state:
.. c:function:: int PyModule_AddObjectRef(PyObject *module, const char *name, PyObject *value)
Add an object to *module* as *name*. This is a convenience function which
can be used from the module's initialization function.
On success, return ``0``. On error, raise an exception and return ``-1``.
Return ``NULL`` if *value* is ``NULL``. It must be called with an exception
raised in this case.
Example usage::
static int
add_spam(PyObject *module, int value)
{
PyObject *obj = PyLong_FromLong(value);
if (obj == NULL) {
return -1;
}
int res = PyModule_AddObjectRef(module, "spam", obj);
Py_DECREF(obj);
return res;
}
The example can also be written without checking explicitly if *obj* is
``NULL``::
static int
add_spam(PyObject *module, int value)
{
PyObject *obj = PyLong_FromLong(value);
int res = PyModule_AddObjectRef(module, "spam", obj);
Py_XDECREF(obj);
return res;
}
Note that ``Py_XDECREF()`` should be used instead of ``Py_DECREF()`` in
this case, since *obj* can be ``NULL``.
.. versionadded:: 3.10
.. c:function:: int PyModule_AddObject(PyObject *module, const char *name, PyObject *value)
Add an object to *module* as *name*. This is a convenience function which can
be used from the module's initialization function. This steals a reference to
*value* on success. Return ``-1`` on error, ``0`` on success.
Similar to :c:func:`PyModule_AddObjectRef`, but steals a reference to
*value* on success (if it returns ``0``).
The new :c:func:`PyModule_AddObjectRef` function is recommended, since it is
easy to introduce reference leaks by misusing the
:c:func:`PyModule_AddObject` function.
.. note::
Unlike other functions that steal references, ``PyModule_AddObject()`` only
decrements the reference count of *value* **on success**.
Unlike other functions that steal references, ``PyModule_AddObject()``
only decrements the reference count of *value* **on success**.
This means that its return value must be checked, and calling code must
:c:func:`Py_DECREF` *value* manually on error. Example usage::
Py_INCREF(spam);
if (PyModule_AddObject(module, "spam", spam) < 0) {
Py_DECREF(module);
Py_DECREF(spam);
return NULL;
}
:c:func:`Py_DECREF` *value* manually on error.
Example usage::
static int
add_spam(PyObject *module, int value)
{
PyObject *obj = PyLong_FromLong(value);
if (obj == NULL) {
return -1;
}
if (PyModule_AddObject(module, "spam", obj) < 0) {
Py_DECREF(obj);
return -1;
}
// PyModule_AddObject() stole a reference to obj:
// Py_DECREF(obj) is not needed here
return 0;
}
The example can also be written without checking explicitly if *obj* is
``NULL``::
static int
add_spam(PyObject *module, int value)
{
PyObject *obj = PyLong_FromLong(value);
if (PyModule_AddObject(module, "spam", obj) < 0) {
Py_XDECREF(obj);
return -1;
}
// PyModule_AddObject() stole a reference to obj:
// Py_DECREF(obj) is not needed here
return 0;
}
Note that ``Py_XDECREF()`` should be used instead of ``Py_DECREF()`` in
this case, since *obj* can be ``NULL``.
.. c:function:: int PyModule_AddIntConstant(PyObject *module, const char *name, long value)
Expand Down
5 changes: 5 additions & 0 deletions Doc/whatsnew/3.10.rst
Original file line number Diff line number Diff line change
Expand Up @@ -374,6 +374,11 @@ New Features
* Added :c:func:`PyUnicode_AsUTF8AndSize` to the limited C API.
(Contributed by Alex Gaynor in :issue:`41784`.)

* Added :c:func:`PyModule_AddObjectRef` function: similar to
:c:func:`PyModule_AddObjectRef` but don't steal a reference to the value on

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@erlend-aasland

erlend-aasland Nov 4, 2020

Contributor

Typo ... => similar to :c:func:PyModule_AddObject

success.
(Contributed by Victor Stinner in :issue:`1635741`.)


Porting to Python 3.10
----------------------
Expand Down
10 changes: 9 additions & 1 deletion Include/modsupport.h
Original file line number Diff line number Diff line change
Expand Up @@ -136,7 +136,15 @@ PyAPI_FUNC(PyObject * const *) _PyArg_UnpackKeywords(
void _PyArg_Fini(void);
#endif /* Py_LIMITED_API */

PyAPI_FUNC(int) PyModule_AddObject(PyObject *, const char *, PyObject *);
// Add an attribute with name 'name' and value 'obj' to the module 'mod.
// On success, return 0 on success.
// On error, raise an exception and return -1.
PyAPI_FUNC(int) PyModule_AddObjectRef(PyObject *mod, const char *name, PyObject *value);

// Similar to PyModule_AddObjectRef() but steal a reference to 'obj'
// (Py_DECREF(obj)) on success (if it returns 0).
PyAPI_FUNC(int) PyModule_AddObject(PyObject *mod, const char *, PyObject *value);

PyAPI_FUNC(int) PyModule_AddIntConstant(PyObject *, const char *, long);
PyAPI_FUNC(int) PyModule_AddStringConstant(PyObject *, const char *, const char *);
#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03090000
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Added :c:func:`PyModule_AddObjectRef` function: similar to
:c:func:`PyModule_AddObjectRef` but don't steal a reference to the value on

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@erlend-aasland

erlend-aasland Nov 4, 2020

Contributor

Typo ... => similar to :c:func:PyModule_AddObject

success. Patch by Victor Stinner.
70 changes: 39 additions & 31 deletions Python/modsupport.c
Original file line number Diff line number Diff line change
Expand Up @@ -634,56 +634,70 @@ va_build_stack(PyObject **small_stack, Py_ssize_t small_stack_len,


int
PyModule_AddObject(PyObject *m, const char *name, PyObject *o)
PyModule_AddObjectRef(PyObject *mod, const char *name, PyObject *value)
{
PyObject *dict;
if (!PyModule_Check(m)) {
if (!PyModule_Check(mod)) {
PyErr_SetString(PyExc_TypeError,
"PyModule_AddObject() needs module as first arg");
"PyModule_AddObjectRef() first argument "
"must be a module");
return -1;
}
if (!o) {
if (!PyErr_Occurred())
PyErr_SetString(PyExc_TypeError,
"PyModule_AddObject() needs non-NULL value");
if (!value) {
if (!PyErr_Occurred()) {
PyErr_SetString(PyExc_SystemError,
"PyModule_AddObjectRef() must be called "
"with an exception raised if value is NULL");
}
return -1;
}

dict = PyModule_GetDict(m);
PyObject *dict = PyModule_GetDict(mod);
if (dict == NULL) {
/* Internal error -- modules must have a dict! */
PyErr_Format(PyExc_SystemError, "module '%s' has no __dict__",
PyModule_GetName(m));
PyModule_GetName(mod));
return -1;
}
if (PyDict_SetItemString(dict, name, o))

if (PyDict_SetItemString(dict, name, value)) {
return -1;
Py_DECREF(o);
}
return 0;
}


int
PyModule_AddObject(PyObject *mod, const char *name, PyObject *value)
{
int res = PyModule_AddObjectRef(mod, name, value);
if (res == 0) {
Py_DECREF(value);
}
return res;
}

int
PyModule_AddIntConstant(PyObject *m, const char *name, long value)
{
PyObject *o = PyLong_FromLong(value);
if (!o)
PyObject *obj = PyLong_FromLong(value);
if (!obj) {
return -1;
if (PyModule_AddObject(m, name, o) == 0)
return 0;
Py_DECREF(o);
return -1;
}
int res = PyModule_AddObjectRef(m, name, obj);
Py_DECREF(obj);
return res;
}

int
PyModule_AddStringConstant(PyObject *m, const char *name, const char *value)
{
PyObject *o = PyUnicode_FromString(value);
if (!o)
PyObject *obj = PyUnicode_FromString(value);
if (!obj) {
return -1;
if (PyModule_AddObject(m, name, o) == 0)
return 0;
Py_DECREF(o);
return -1;
}
int res = PyModule_AddObjectRef(m, name, obj);
Py_DECREF(obj);
return res;
}

int
Expand All @@ -696,11 +710,5 @@ PyModule_AddType(PyObject *module, PyTypeObject *type)
const char *name = _PyType_Name(type);
assert(name != NULL);

Py_INCREF(type);
if (PyModule_AddObject(module, name, (PyObject *)type) < 0) {
Py_DECREF(type);
return -1;
}

return 0;
return PyModule_AddObjectRef(module, name, (PyObject *)type);
}

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