PyFunctionObject crash the programm in Py_Finalize if it has being set item in PyTuple

Question

I need get list of function name and signatures by python file. Python function inspect.signature can get me function signature. But inspect.signature need a function object (PyFunctionObject). inspect.getmembers can return such object. But if I set PyFunctionObject as item in PyTuple, when Py_Finalize is executed - I get error. Also, I'm using Qt.

So line PyTuple_SetItem(pFuncLink_arg, 0, pGetmember_tupleList); result error.

Code:.

PyObject *pName, *pModule;
PyObject *pInspect_module_name, *pInspect_module;
PyObject *pGetmember_function, *pGetmember_call_args, *pGetmembers_reply, *pGetsignature_function, *pGetmember_itemList, *pGetmember_tupleList;
PyObject *pFuncName, *pFuncLink_arg, *pFuncSign;

Py_Initialize();

QFileInfo fileInfo(QFile("X:/Projects/p-text.py"));
QString absPath = fileInfo.absolutePath();

QString fileName = fileInfo.baseName();

PyObject* sysPath = PySys_GetObject((char*)"path"); 
PyObject* programName = PyUnicode_FromString(absPath.toAscii());
PyList_Append(sysPath, programName);

pName = PyUnicode_FromString(fileName.toLatin1());
pModule = PyImport_Import(pName);
Py_DECREF(pName);

if (pModule != NULL){
    pInspect_module_name = PyUnicode_DecodeFSDefault("inspect");
    pInspect_module = PyImport_Import(pInspect_module_name);
    pGetmember_function = PyObject_GetAttrString(pInspect_module, "getmembers");    
    pGetsignature_function = PyObject_GetAttrString(pInspect_module, "signature");

    pGetmember_call_args = PyTuple_New(1);
    PyTuple_SetItem(pGetmember_call_args, 0, pModule);
    pGetmembers_reply = PyObject_CallObject(pGetmember_function, pGetmember_call_args);

    if (pGetmembers_reply){
        Py_ssize_t const num_args = PyList_Size(pGetmembers_reply);
        for (Py_ssize_t i = 0; i < num_args; ++i){
            pGetmember_itemList = PyList_GetItem(pGetmembers_reply, i);
            pGetmember_tupleList =  PyTuple_GetItem(pGetmember_itemList, 1);

            if (PyFunction_Check(pGetmember_tupleList)){
                pFuncName =  PyTuple_GetItem(pGetmember_itemList, 0);
                QString funcName = PyObjectToString(pFuncName);
                    Py_DECREF(pFuncName);

                pFuncLink_arg = PyTuple_New(1);
                PyTuple_SetItem(pFuncLink_arg, 0, pGetmember_tupleList);

                pFuncSign = PyObject_CallObject(pGetsignature_function, pFuncLink_arg);

                if (pFuncSign == NULL) {
                    if (PyErr_Occurred()) {
                        PyErr_Print(); 
                    }
                    return;
                }

                QString funcSign = PyObjectToString(pFuncSign);

                Py_DECREF(pFuncSign);

                cout<<funcSign.toStdString()<<endl;
            }

            Py_DECREF(pGetmember_tupleList);
            Py_DECREF(pGetmember_itemList);
        }
    }
    Py_DECREF(pInspect_module_name);
    Py_DECREF(pInspect_module);
    Py_DECREF(pGetmember_function);
    Py_DECREF(pGetsignature_function);
    Py_DECREF(pGetmember_call_args);
}
else {
    PyErr_Print();
}

Py_Finalize();

Py_Finalize() throws an error "project_name.exe has triggered a breakpoint"

Answer 1

Reference counting error.

PyTuple_GetItem returns a "borrowed reference". You don't own pGetmember_tupleList.

PyTuple_SetItem (find it at the same link...) "steals a reference", i.e. assumes you do own pGetmember_tupleList before the call but you don't own it after the call.

You need to add a Py_INCREF(pGetmember_tupleList) after getting it.

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You have a separate, related reference counting error with pFuncName - you decref a borrowed reference that you don't own. I suspect there are probably other reference counting errors here too...

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You also have no error checking; almost every Python call should be followed by a check to see if it raised an exception (usually for a NULL pointer).