PyObject_GetItem() raises a KeyError if the key is not found in a mapping. In some cases it should be treated as any other error, but in other cases it should be caught and suppressed. The repeating pattern ofPyObject_GetItem() followed byPyErr_ExceptionMatches(PyExc_KeyError) andPyErr_Clear() occurs 7 times inPython/bytecodes.c and at least 5 times in other files.

I propose to add private helper_PyMapping_LookupItem() which combines these three calls to make the code clearer. It also has a special case for exact dict, so eliminates even more repeating code. For example:

     PyObject *m;-    if (PyDict_CheckExact(modules)) {-        m = Py_XNewRef(PyDict_GetItemWithError(modules, name));-    }-    else {-        m = PyObject_GetItem(modules, name);-        if (_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {-            _PyErr_Clear(tstate);-        }-    }-    if (_PyErr_Occurred(tstate)) {+    if (_PyMapping_LookupItem(modules, name, &m) < 0) {         return NULL;     }

The interface of_PyMapping_LookupItem() is very similar to other private helper_PyObject_LookupAttr() (see#76752) and to a proposed new C API for PyDict (see#106004).

Linked PRs

• gh-106307: Add PyMapping_GetOptionalItem() #106308