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[C API] Deprecate calling PyObject_SetAttr(obj, attr, NULL) with an exception set #135075
Description
The issue gh-106572 changed PyObject_DelAttr() and PyObject_DelAttrString() implementation from a macro to a function (commit 1f2921b).
Now I propose deprecating calls PyObject_SetAttr(obj, attr, NULL) and PyObject_SetAttrString(obj, attr, NULL) with an exception set to help detecting bugs. When the code creating the attribute value failed, it should be handled before calling PyObject_SetAttr[String)() to avoid deleting the attribute by mistake.
The change affects also the stable ABI.
I also propose to treat this deprecation as an error in Python 3.17.
Example of buggy code:
PyObject *module = PyUnicode_FromString(module_name);
int res = PyObject_SetAttrString(ns, "__module__", module);
Py_DECREF(module);
Correct code:
PyObject *module = PyUnicode_FromString(module_name);
if (module == NULL) { // <=== CHECK VALUE ===
goto error;
}
int res = PyObject_SetAttrString(ns, "__module__", module);
Py_DECREF(module);
Activity
pythongh-135075: Deprecate PyObject_SetAttr(obj, name, NULL) with exc
vstinner commentedon Jun 3, 2025
It seems like currently, it's not really possible to call PyObject_SetAttr() with NULL and an exception set. For example, if
type->tp_setattroisPyObject_GenericSetAttr(), it fails with an assertion error:vstinner commentedon Jun 3, 2025
Maybe we should directly treat this case (calling PyObject_SetAttr() with NULL value and an exception set) as an error, rather than trying to emit a
DeprecationWarning.pythongh-135075: Make PyObject_SetAttr() fail with NULL value and exc…
gh-135075: Make PyObject_SetAttr() fail with NULL value and exception (…
pythongh-135075: Make PyObject_SetAttr() fail with NULL value and exc…
pythongh-135075: Make PyObject_SetAttr() fail with NULL value and exc…
pythongh-135075: Make PyObject_SetAttr() fail with NULL value and exc…
pythongh-135075: Make PyObject_SetAttr() fail with NULL value and exc…
pythongh-135075: Make PyObject_SetAttr() fail with NULL value and exc…