Debugging mixed C++/embedded Python

Question

Firstly my problem is similar to this one:

However although the description in that case is very helpful, it doesn't alas contain all the information needed to debug a mixed C++/embedded Python app.

Background: I have a C++ app that is calling Python code with some argument:

bool              
ui::runLUOvershoot4(PyObject*inData)
{
    // Get the python module.
    PyObject* const pName = PyBytes_FromString("lu_overshoot4");
    PyObject* pModule = nullptr;

    PyObject* const pMod = PyImport_AddModule("lu_overshoot4");
    if (pMod != nullptr) {
        pModule = PyImport_ReloadModule(pMod);
    }
    /* NB pMod is borrowed and must not be Py_DECREF-ed */

    if (pModule == nullptr) {
        PyErr_Print();
        return false;
    }
    Py_DECREF(pName);

    // Get the dictionary for the lu_overshoot4 module
    PyObject* const pDict = PyModule_GetDict(pModule);
    Py_DECREF(pModule);

    // Get the function in the dictionary
    PyObject* const pFunc = PyDict_GetItemString(pDict, "LU_Overshoot4");
    if (pFunc == nullptr) {
        PyErr_Print();
        return false;
    }
    Py_INCREF(pFunc);

    if (pFunc && PyCallable_Check(pFunc)) {

        // Call the python func with inData as arg
        PyObject* arglist = Py_BuildValue("(O)", inData);

        PyObject* const pValue = PyObject_Call(pFunc, arglist, nullptr);
        if (pValue == nullptr) {
            PyErr_Print();
            return false;
        }
        Py_DECREF(pFunc);
        return true;
    }
    return false;
}

All works as expected. But I want to be able to step in the debugger from the C++ PyObject_Call into the python code. So far I have been able to do this only if I start the C++ code without the debugger, then attach the debugger to the running process. If I try and start in the debugger, the breakpoints in the python code are disabled with the tooltip 'The breakpoint will not currently be hit. No symbols have been loaded for this document'.

A little detail on the setup: this is a Visual Studio 2022 solution with a C++ project (with the debugger to launch being the Python/Native Debugger) and a Python project containing the python files. It's not clear to me what settings to give the Python project, what I have is in the General tab,

Startup File -
Working Directory - .
Windows Application - ticked (makes no difference though)
Interpreter - env(Python 3.8 64-bit).

In the Debug tab,

Search Paths - .;\env
Script args -
Interpreter Path - \env
Interpreter Args -
Environment Variables -
Debug - 'Enable native code debugging' checked.

The python project's Python Environment was set up with a virtual env, set to the \env directory, which contains the include/Lib/Scripts/share dirs and python.exe, python38.dll, python.pdb etc. i.e. python installation and pdb files. This is how (I believe) 'Lambda' describes their setup.

One of the issues I faced was that at first VS2022 (v 17.2.6) did not give the option of setting the debugger to python/native; a fix is described in https://docs.microsoft.com/en-us/answers/questions/860222/the-option-34pythonnative-debugging34-is-missing-f.html. But with that set and starting the debugger with F5, it is not possible to step into Python code from C++ or break on Python code - only if debugging is done by attaching to the running process.

Any help gratefully received.

Debugging mixed C++/embedded Python

0 Answers