gh-106307: Add _PyMapping_LookupItem()

Replacement of PyObject_GetItem() which doesn't raise KeyError.

  int _PyMapping_LookupItem(PyObject *obj, PyObject *key, PyObject **result)

Return 1 and set *result != NULL if a key is found.
Return 0 and set *result == NULL if a key is not found;
a KeyError is silenced.
Return -1 and set *result == NULL if an error other than KeyError
is raised.

Author: serhiy-storchaka

Include/cpython/object.h

@@ -320,6 +320,17 @@ PyAPI_FUNC(int)
 _PyObject_GenericSetAttrWithDict(PyObject *, PyObject *,
                                  PyObject *, PyObject *);
 
+/* Replacements of PyObject_GetItem() which don't raise KeyError.
+
+   Return 1 and set *result != NULL if a key is found.
+   Return 0 and set *result == NULL if a key is not found;
+   a KeyError is silenced.
+   Return -1 and set *result == NULL if an error other than KeyError
+   is raised.
+*/
+PyAPI_FUNC(int) _PyMapping_LookupItem(PyObject *, PyObject *, PyObject **);
+PyAPI_FUNC(int) _PyMapping_LookupItemString(PyObject *, const char *, PyObject **);
+
 PyAPI_FUNC(PyObject *) _PyObject_FunctionStr(PyObject *);
 
 /* Safely decref `dst` and set `dst` to `src`.

Modules/_lzmamodule.c

@@ -242,15 +242,10 @@ parse_filter_spec_lzma(_lzma_state *state, PyObject *spec)
     /* First, fill in default values for all the options using a preset.
        Then, override the defaults with any values given by the caller. */
 
-    preset_obj = PyMapping_GetItemString(spec, "preset");
-    if (preset_obj == NULL) {
-        if (PyErr_ExceptionMatches(PyExc_KeyError)) {
-            PyErr_Clear();
-        }
-        else {
-            return NULL;
-        }
-    } else {
+    if (_PyMapping_LookupItemString(spec, "preset", &preset_obj) < 0) {
+        return NULL;
+    }
+    if (preset_obj != NULL) {
         int ok = uint32_converter(preset_obj, &preset);
         Py_DECREF(preset_obj);
         if (!ok) {
@@ -347,11 +342,12 @@ lzma_filter_converter(_lzma_state *state, PyObject *spec, void *ptr)
                         "Filter specifier must be a dict or dict-like object");
         return 0;
     }
-    id_obj = PyMapping_GetItemString(spec, "id");
+    if (_PyMapping_LookupItemString(spec, "id", &id_obj) < 0) {
+        return 0;
+    }
     if (id_obj == NULL) {
-        if (PyErr_ExceptionMatches(PyExc_KeyError))
-            PyErr_SetString(PyExc_ValueError,
-                            "Filter specifier must have an \"id\" entry");
+        PyErr_SetString(PyExc_ValueError,
+                        "Filter specifier must have an \"id\" entry");
         return 0;
     }
     f->id = PyLong_AsUnsignedLongLong(id_obj);

Modules/_pickle.c

@@ -4438,13 +4438,9 @@ save(PickleState *st, PicklerObject *self, PyObject *obj, int pers_save)
             Py_INCREF(reduce_func);
         }
     } else {
-        reduce_func = PyObject_GetItem(self->dispatch_table,
-                                       (PyObject *)type);
-        if (reduce_func == NULL) {
-            if (PyErr_ExceptionMatches(PyExc_KeyError))
-                PyErr_Clear();
-            else
-                goto error;
+        if (_PyMapping_LookupItem(self->dispatch_table, (PyObject *)type,
+                                  &reduce_func) < 0) {
+            goto error;
         }
     }
     if (reduce_func != NULL) {

Objects/abstract.c

@@ -199,6 +199,30 @@ PyObject_GetItem(PyObject *o, PyObject *key)
     return type_error("'%.200s' object is not subscriptable", o);
 }
 
+int
+_PyMapping_LookupItem(PyObject *o, PyObject *key, PyObject **pvalue)
+{
+    if (PyDict_CheckExact(o)) {
+        *pvalue = PyDict_GetItemWithError(o, key);  /* borrowed */
+        if (*pvalue) {
+            Py_INCREF(*pvalue);
+            return 1;
+        }
+        return PyErr_Occurred() ? -1 : 0;
+    }
+
+    *pvalue = PyObject_GetItem(o, key);
+    if (*pvalue) {
+        return 1;
+    }
+    assert(PyErr_Occurred());
+    if (!PyErr_ExceptionMatches(PyExc_KeyError)) {
+        return -1;
+    }
+    PyErr_Clear();
+    return 0;
+}
+
 int
 PyObject_SetItem(PyObject *o, PyObject *key, PyObject *value)
 {
@@ -2366,6 +2390,22 @@ PyMapping_GetItemString(PyObject *o, const char *key)
     return r;
 }
 
+int
+_PyMapping_LookupItemString(PyObject *o, const char *key, PyObject **pvalue)
+{
+    if (key == NULL) {
+        null_error();
+        return -1;
+    }
+    PyObject *okey = PyUnicode_FromString(key);
+    if (okey == NULL) {
+        return -1;
+    }
+    int r = _PyMapping_LookupItem(o, okey, pvalue);
+    Py_DECREF(okey);
+    return r;
+}
+
 int
 PyMapping_SetItemString(PyObject *o, const char *key, PyObject *value)
 {

Python/bytecodes.c

@@ -1086,26 +1086,11 @@ dummy_func(
         }
 
         inst(LOAD_BUILD_CLASS, ( -- bc)) {
-            if (PyDict_CheckExact(BUILTINS())) {
-                bc = _PyDict_GetItemWithError(BUILTINS(),
-                                              &_Py_ID(__build_class__));
-                if (bc == NULL) {
-                    if (!_PyErr_Occurred(tstate)) {
-                        _PyErr_SetString(tstate, PyExc_NameError,
-                                         "__build_class__ not found");
-                    }
-                    ERROR_IF(true, error);
-                }
-                Py_INCREF(bc);
-            }
-            else {
-                bc = PyObject_GetItem(BUILTINS(), &_Py_ID(__build_class__));
-                if (bc == NULL) {
-                    if (_PyErr_ExceptionMatches(tstate, PyExc_KeyError))
-                        _PyErr_SetString(tstate, PyExc_NameError,
-                                         "__build_class__ not found");
-                    ERROR_IF(true, error);
-                }
+            ERROR_IF(_PyMapping_LookupItem(BUILTINS(), &_Py_ID(__build_class__), &bc) < 0, error);
+            if (bc == NULL) {
+                _PyErr_SetString(tstate, PyExc_NameError,
+                                 "__build_class__ not found");
+                ERROR_IF(true, error);
             }
         }
 
@@ -1280,25 +1265,9 @@ dummy_func(
 
         op(_LOAD_FROM_DICT_OR_GLOBALS, (mod_or_class_dict -- v)) {
             PyObject *name = GETITEM(FRAME_CO_NAMES, oparg);
-            if (PyDict_CheckExact(mod_or_class_dict)) {
-                v = PyDict_GetItemWithError(mod_or_class_dict, name);
-                if (v != NULL) {
-                    Py_INCREF(v);
-                }
-                else if (_PyErr_Occurred(tstate)) {
-                    Py_DECREF(mod_or_class_dict);
-                    goto error;
-                }
-            }
-            else {
-                v = PyObject_GetItem(mod_or_class_dict, name);
-                if (v == NULL) {
-                    if (!_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
-                        Py_DECREF(mod_or_class_dict);
-                        goto error;
-                    }
-                    _PyErr_Clear(tstate);
-                }
+            if (_PyMapping_LookupItem(mod_or_class_dict, name, &v) < 0) {
+                Py_DECREF(mod_or_class_dict);
+                goto error;
             }
             Py_DECREF(mod_or_class_dict);
             if (v == NULL) {
@@ -1310,28 +1279,14 @@ dummy_func(
                     goto error;
                 }
                 else {
-                    if (PyDict_CheckExact(BUILTINS())) {
-                        v = PyDict_GetItemWithError(BUILTINS(), name);
-                        if (v == NULL) {
-                            if (!_PyErr_Occurred(tstate)) {
-                                format_exc_check_arg(
-                                        tstate, PyExc_NameError,
-                                        NAME_ERROR_MSG, name);
-                            }
-                            goto error;
-                        }
-                        Py_INCREF(v);
+                    if (_PyMapping_LookupItem(BUILTINS(), name, &v) < 0) {
+                        goto error;
                     }
-                    else {
-                        v = PyObject_GetItem(BUILTINS(), name);
-                        if (v == NULL) {
-                            if (_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
-                                format_exc_check_arg(
-                                            tstate, PyExc_NameError,
-                                            NAME_ERROR_MSG, name);
-                            }
-                            goto error;
-                        }
+                    if (v == NULL) {
+                        format_exc_check_arg(
+                                    tstate, PyExc_NameError,
+                                    NAME_ERROR_MSG, name);
+                        goto error;
                     }
                 }
             }
@@ -1381,19 +1336,14 @@ dummy_func(
                 /* Slow-path if globals or builtins is not a dict */
 
                 /* namespace 1: globals */
-                v = PyObject_GetItem(GLOBALS(), name);
+                ERROR_IF(_PyMapping_LookupItem(GLOBALS(), name, &v) < 0, error);
                 if (v == NULL) {
-                    ERROR_IF(!_PyErr_ExceptionMatches(tstate, PyExc_KeyError), error);
-                    _PyErr_Clear(tstate);
-
                     /* namespace 2: builtins */
-                    v = PyObject_GetItem(BUILTINS(), name);
+                    ERROR_IF(_PyMapping_LookupItem(BUILTINS(), name, &v) < 0, error);
                     if (v == NULL) {
-                        if (_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
-                            format_exc_check_arg(
-                                        tstate, PyExc_NameError,
-                                        NAME_ERROR_MSG, name);
-                        }
+                        format_exc_check_arg(
+                                    tstate, PyExc_NameError,
+                                    NAME_ERROR_MSG, name);
                         ERROR_IF(true, error);
                     }
                 }
@@ -1466,25 +1416,9 @@ dummy_func(
             assert(class_dict);
             assert(oparg >= 0 && oparg < _PyFrame_GetCode(frame)->co_nlocalsplus);
             name = PyTuple_GET_ITEM(_PyFrame_GetCode(frame)->co_localsplusnames, oparg);
-            if (PyDict_CheckExact(class_dict)) {
-                value = PyDict_GetItemWithError(class_dict, name);
-                if (value != NULL) {
-                    Py_INCREF(value);
-                }
-                else if (_PyErr_Occurred(tstate)) {
-                    Py_DECREF(class_dict);
-                    goto error;
-                }
-            }
-            else {
-                value = PyObject_GetItem(class_dict, name);
-                if (value == NULL) {
-                    if (!_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
-                        Py_DECREF(class_dict);
-                        goto error;
-                    }
-                    _PyErr_Clear(tstate);
-                }
+            if (_PyMapping_LookupItem(class_dict, name, &value) < 0) {
+                Py_DECREF(class_dict);
+                goto error;
             }
             Py_DECREF(class_dict);
             if (!value) {
@@ -1622,10 +1556,8 @@ dummy_func(
             }
             else {
                 /* do the same if locals() is not a dict */
-                ann_dict = PyObject_GetItem(LOCALS(), &_Py_ID(__annotations__));
+                ERROR_IF(_PyMapping_LookupItem(LOCALS(), &_Py_ID(__annotations__), &ann_dict) < 0, error);
                 if (ann_dict == NULL) {
-                    ERROR_IF(!_PyErr_ExceptionMatches(tstate, PyExc_KeyError), error);
-                    _PyErr_Clear(tstate);
                     ann_dict = PyDict_New();
                     ERROR_IF(ann_dict == NULL, error);
                     err = PyObject_SetItem(LOCALS(), &_Py_ID(__annotations__),