Faster attribute lookup

When an attribute lookup fails, Python spends a significant chunk of CPU
cycles formatting and then raising an exception.

The ``nb::getattr(object, key, default)`` API provides a fallback
``default`` value in the case of an error. The expense of raising an
exception is therefore not wanted here.

This commit avoids this exception by

- using the new ``PyObject_GetOptionalAttr()`` function on Python 3.13+
- using an internal ``_PyObject_LookupAttr()`` API before Python 3.13.
- on the 3.12 stable API, using ``PyObject_HasAttr()`` before doing the lookup.

Author: wjakob

cmake/darwin-ld-cpython.sym

@@ -867,6 +867,7 @@
 -U __PyObject_GC_New
 -U __PyObject_GC_NewVar
 -U __PyObject_GC_Resize
+-U __PyObject_LookupAttr
 -U __PyObject_MakeTpCall
 -U __PyObject_New
 -U __PyObject_NewVar

src/common.cpp

@@ -371,20 +371,59 @@ PyObject *getattr(PyObject *obj, PyObject *key) {
     return res;
 }
 
-PyObject *getattr(PyObject *obj, const char *key, PyObject *def) noexcept {
-    PyObject *res = PyObject_GetAttrString(obj, key);
-    if (res)
+PyObject *getattr(PyObject *obj, const char *key_, PyObject *def) noexcept {
+#if (defined(Py_LIMITED_API) && PY_LIMITED_API < 0x030d0000) || defined(PYPY_VERSION)
+    str key(key_);
+    if (PyObject_HasAttr(obj, key.ptr())) {
+        PyObject *res = PyObject_GetAttr(obj, key.ptr());
+        if (res)
+            return res;
+        PyErr_Clear();
+    }
+#else
+    PyObject *res;
+    int rv;
+
+    #if PY_VERSION_HEX < 0x030d0000
+        rv = _PyObject_LookupAttr(obj, str(key_).ptr(), &res);
+    #else
+        rv = PyObject_GetOptionalAttrString(obj, key_, &res);
+    #endif
+
+    if (rv == 1)
         return res;
-    PyErr_Clear();
+    else if (rv < 0)
+        PyErr_Clear();
+#endif
+
     Py_XINCREF(def);
     return def;
 }
 
 PyObject *getattr(PyObject *obj, PyObject *key, PyObject *def) noexcept {
-    PyObject *res = PyObject_GetAttr(obj, key);
-    if (res)
+#if (defined(Py_LIMITED_API) && PY_LIMITED_API < 0x030d0000) || defined(PYPY_VERSION)
+    if (PyObject_HasAttr(obj, key)) {
+        PyObject *res = PyObject_GetAttr(obj, key);
+        if (res)
+            return res;
+        PyErr_Clear();
+    }
+#else
+    PyObject *res;
+    int rv;
+
+    #if PY_VERSION_HEX < 0x030d0000
+        rv = _PyObject_LookupAttr(obj, key, &res);
+    #else
+        rv = PyObject_GetOptionalAttr(obj, key, &res);
+    #endif
+
+    if (rv == 1)
         return res;
-    PyErr_Clear();
+    else if (rv < 0)
+        PyErr_Clear();
+#endif
+
     Py_XINCREF(def);
     return def;
 }