gh-102213: Optimizing the Performance of __getattr__ #102213

Include/object.h

@@ -304,6 +304,7 @@ PyAPI_FUNC(int) PyObject_SetAttr(PyObject *, PyObject *, PyObject *);
 PyAPI_FUNC(int) PyObject_HasAttr(PyObject *, PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_SelfIter(PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_GenericGetAttr(PyObject *, PyObject *);
+PyAPI_FUNC(PyObject *) PyObject_GenericTryGetAttr(PyObject *, PyObject *);
 PyAPI_FUNC(int) PyObject_GenericSetAttr(PyObject *, PyObject *, PyObject *);
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03030000
 PyAPI_FUNC(int) PyObject_GenericSetDict(PyObject *, PyObject *, void *);

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

@@ -1364,6 +1364,12 @@ 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

@@ -8248,14 +8248,16 @@ _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);