PySide2 embedded in C++ application only has QCoreApplication instead of full QApplication

[wrosecrans]

So, basically, my question is, how can I find widgets created in C++, when I am using Python embedded in a C++ Application. I made an example of what I am talking about...

#include <pybind11/embed.h> // everything needed for embedding

#include <iostream>
#include <QWidget>
#include <QApplication>

namespace py = pybind11;

void pystuff() {

    py::print("Hello, from Python!"); // use the Python API
    py::exec("import PySide2");
    py::exec("from PySide2 import QtWidgets");
    py::exec("app = QtWidgets.QApplication.instance()");

    py::exec("print(type(app))");
    py::exec("import sys");
    py::exec("print(sys.version)");
    py::exec("print(PySide2.__version__)");
    py::exec("w = QtWidgets.QWidget()");
    py::exec("w.show(); w.setWindowTitle('Python')");
    py::exec("print('', flush=True)");

}

int main(int argc, char *argv[])
{
    QApplication *a = new QApplication(argc, argv);
    py::scoped_interpreter guard{}; // start the interpreter and keep it alive

    QWidget w;
    w.setWindowTitle("C++");
    w.show();

    a->connect(a, &QGuiApplication::applicationStateChanged, [a](Qt::ApplicationState state) {
        if (state == Qt::ApplicationActive) {
            pystuff();
            std::cout << "Checking all Widgets..." << std::endl;
            for (auto && widget : a->allWidgets() ) {
                std::cout << widget->windowTitle().toStdString() << std::endl;
            }
        }
    });

    return a->exec();
}

The result of this is that I have created two windows. One window was created in C++. The other was created using Python. That much works. After I run the python, in C++ I iterate over "QApplication->allWidgets() " and I can see the widget I created in Python, so I could theoretically add it to a layout or whatever in C++. But, I can't do the reverse because the type of py::exec("app = QtWidgets.QApplication.instance()");
is just a QCoreApplication instead of a full QApplication object. So it has no allWidgets() method for me to interrogate. Which is super confusing. Here's the output:

Hello, from Python!
<class 'PySide2.QtCore.QCoreApplication'>
3.7.5 (default, Nov  1 2019, 02:16:32) 
[Clang 11.0.0 (clang-1100.0.33.8)]
5.12.5a1.dev1566934103

Checking all Widgets...
Python
C++

WTF?

[jsulm]

@wrosecrans Did you try to cast app to QApplication? QApplication inderectly inherits QCoreApplication.
instance() returns pointer to QCoreApplication according to Qt documentation.