bpo-32571: Avoid raising unneeded AttributeError and silencing it in C code (GH-5222)

Add two new private APIs: _PyObject_LookupAttr() and _PyObject_LookupAttrId()

Python/_warnings.c

@@ -80,11 +80,8 @@ get_warnings_attr(_Py_Identifier *attr_id, int try_import)
             return NULL;
     }
 
-    obj = _PyObject_GetAttrId(warnings_module, attr_id);
+    (void)_PyObject_LookupAttrId(warnings_module, attr_id, &obj);
     Py_DECREF(warnings_module);
-    if (obj == NULL && PyErr_ExceptionMatches(PyExc_AttributeError)) {
-        PyErr_Clear();
-    }
     return obj;
 }
 
@@ -893,13 +890,10 @@ get_source_line(PyObject *module_globals, int lineno)
     Py_INCREF(module_name);
 
     /* Make sure the loader implements the optional get_source() method. */
-    get_source = _PyObject_GetAttrId(loader, &PyId_get_source);
+    (void)_PyObject_LookupAttrId(loader, &PyId_get_source, &get_source);
     Py_DECREF(loader);
     if (!get_source) {
         Py_DECREF(module_name);
-        if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
-            PyErr_Clear();
-        }
         return NULL;
     }
     /* Call get_source() to get the source code. */

Python/bltinmodule.c

@@ -71,12 +71,10 @@ update_bases(PyObject *bases, PyObject *const *args, Py_ssize_t nargs)
             }
             continue;
         }
-        meth = _PyObject_GetAttrId(base, &PyId___mro_entries__);
+        if (_PyObject_LookupAttrId(base, &PyId___mro_entries__, &meth) < 0) {
+            goto error;
+        }
         if (!meth) {
-            if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
-                goto error;
-            }
-            PyErr_Clear();
             if (new_bases) {
                 if (PyList_Append(new_bases, base) < 0) {
                     goto error;
@@ -218,18 +216,11 @@ builtin___build_class__(PyObject *self, PyObject *const *args, Py_ssize_t nargs,
     }
     /* else: meta is not a class, so we cannot do the metaclass
        calculation, so we will use the explicitly given object as it is */
-    prep = _PyObject_GetAttrId(meta, &PyId___prepare__);
-    if (prep == NULL) {
-        if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
-            PyErr_Clear();
-            ns = PyDict_New();
-        }
-        else {
-            Py_DECREF(meta);
-            Py_XDECREF(mkw);
-            Py_DECREF(bases);
-            return NULL;
-        }
+    if (_PyObject_LookupAttrId(meta, &PyId___prepare__, &prep) < 0) {
+        ns = NULL;
+    }
+    else if (prep == NULL) {
+        ns = PyDict_New();
     }
     else {
         PyObject *pargs[2] = {name, bases};
@@ -1127,8 +1118,7 @@ builtin_getattr(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
         return NULL;
     }
     if (dflt != NULL) {
-        result = _PyObject_GetAttrWithoutError(v, name);
-        if (result == NULL && !PyErr_Occurred()) {
+        if (_PyObject_LookupAttr(v, name, &result) == 0) {
             Py_INCREF(dflt);
             return dflt;
         }
@@ -1191,13 +1181,12 @@ builtin_hasattr_impl(PyObject *module, PyObject *obj, PyObject *name)
                         "hasattr(): attribute name must be string");
         return NULL;
     }
-    v = _PyObject_GetAttrWithoutError(obj, name);
-    if (v == NULL) {
-        if (!PyErr_Occurred()) {
-            Py_RETURN_FALSE;
-        }
+    if (_PyObject_LookupAttr(obj, name, &v) < 0) {
         return NULL;
     }
+    if (v == NULL) {
+        Py_RETURN_FALSE;
+    }
     Py_DECREF(v);
     Py_RETURN_TRUE;
 }

Python/ceval.c

@@ -4813,13 +4813,12 @@ import_from(PyObject *v, PyObject *name)
     _Py_IDENTIFIER(__name__);
     PyObject *fullmodname, *pkgname, *pkgpath, *pkgname_or_unknown, *errmsg;
 
-    x = PyObject_GetAttr(v, name);
-    if (x != NULL || !PyErr_ExceptionMatches(PyExc_AttributeError))
+    if (_PyObject_LookupAttr(v, name, &x) != 0) {
         return x;
+    }
     /* Issue #17636: in case this failed because of a circular relative
        import, try to fallback on reading the module directly from
        sys.modules. */
-    PyErr_Clear();
     pkgname = _PyObject_GetAttrId(v, &PyId___name__);
     if (pkgname == NULL) {
         goto error;
@@ -4881,21 +4880,20 @@ import_all_from(PyObject *locals, PyObject *v)
 {
     _Py_IDENTIFIER(__all__);
     _Py_IDENTIFIER(__dict__);
-    PyObject *all = _PyObject_GetAttrId(v, &PyId___all__);
-    PyObject *dict, *name, *value;
+    PyObject *all, *dict, *name, *value;
     int skip_leading_underscores = 0;
     int pos, err;
 
+    if (_PyObject_LookupAttrId(v, &PyId___all__, &all) < 0) {
+        return -1; /* Unexpected error */
+    }
     if (all == NULL) {
-        if (!PyErr_ExceptionMatches(PyExc_AttributeError))
-            return -1; /* Unexpected error */
-        PyErr_Clear();
-        dict = _PyObject_GetAttrId(v, &PyId___dict__);
+        if (_PyObject_LookupAttrId(v, &PyId___dict__, &dict) < 0) {
+            return -1;
+        }
         if (dict == NULL) {
-            if (!PyErr_ExceptionMatches(PyExc_AttributeError))
-                return -1;
             PyErr_SetString(PyExc_ImportError,
-            "from-import-* object has no __dict__ and no __all__");
+                    "from-import-* object has no __dict__ and no __all__");
             return -1;
         }
         all = PyMapping_Keys(dict);

Python/codecs.c

@@ -540,15 +540,11 @@ PyObject * _PyCodec_LookupTextEncoding(const char *encoding,
      * attribute.
      */
     if (!PyTuple_CheckExact(codec)) {
-        attr = _PyObject_GetAttrId(codec, &PyId__is_text_encoding);
-        if (attr == NULL) {
-            if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
-                PyErr_Clear();
-            } else {
-                Py_DECREF(codec);
-                return NULL;
-            }
-        } else {
+        if (_PyObject_LookupAttrId(codec, &PyId__is_text_encoding, &attr) < 0) {
+            Py_DECREF(codec);
+            return NULL;
+        }
+        if (attr != NULL) {
             is_text_codec = PyObject_IsTrue(attr);
             Py_DECREF(attr);
             if (is_text_codec <= 0) {