gh-102213: Optimize the performance of __getattr__ (GH-102248)

When __getattr__ is defined, python with try to find an attribute using _PyObject_GenericGetAttrWithDict
find nothing is reasonable so we don't need an exception, it will hurt performance.

Include/internal/pycore_object.h

@@ -370,6 +370,7 @@ extern void _PyObject_FreeInstanceAttributes(PyObject *obj);
 extern int _PyObject_IsInstanceDictEmpty(PyObject *);
 extern int _PyType_HasSubclasses(PyTypeObject *);
 extern PyObject* _PyType_GetSubclasses(PyTypeObject *);
+extern PyObject* _PyObject_GenericTryGetAttr(PyObject *, PyObject *);
 
 // Access macro to the members which are floating "behind" the object
 static inline PyMemberDef* _PyHeapType_GET_MEMBERS(PyHeapTypeObject *etype) {

Misc/NEWS.d/next/Core and Builtins/2023-02-26-13-12-55.gh-issue-102213.fTH8X7.rst

@@ -0,0 +1 @@
+Fix performance loss when accessing an object's attributes with ``__getattr__``  defined.

Objects/object.c

@@ -1405,6 +1405,12 @@ PyObject_GenericGetAttr(PyObject *obj, PyObject *name)
     return _PyObject_GenericGetAttrWithDict(obj, name, NULL, 0);
 }
 
+PyObject *
+_PyObject_GenericTryGetAttr(PyObject *obj, PyObject *name)
+{
+    return _PyObject_GenericGetAttrWithDict(obj, name, NULL, 1);
+}
+
 int
 _PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
                                  PyObject *value, PyObject *dict)

Objects/typeobject.c

@@ -8247,14 +8247,17 @@ _Py_slot_tp_getattr_hook(PyObject *self, PyObject *name)
         (Py_IS_TYPE(getattribute, &PyWrapperDescr_Type) &&
          ((PyWrapperDescrObject *)getattribute)->d_wrapped ==
          (void *)PyObject_GenericGetAttr))
-        res = PyObject_GenericGetAttr(self, name);
+        /* finding nothing is reasonable when __getattr__ is defined */
+        res = _PyObject_GenericTryGetAttr(self, name);
     else {
         Py_INCREF(getattribute);
         res = call_attribute(self, getattribute, name);
         Py_DECREF(getattribute);
     }
-    if (res == NULL && PyErr_ExceptionMatches(PyExc_AttributeError)) {
-        PyErr_Clear();
+    if (res == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
+            PyErr_Clear();
+        }
         res = call_attribute(self, getattr, name);
     }
     Py_DECREF(getattr);