Launched PySide2 app from Qt C++ is extremelly slow

[Please_Help_me_D]

Hi,

After few days of struggling with binding Qt with PySide2 I finaly launched python module from Qt C++. Look at the picture below:

There two instances of the same .py module: to the left is fast and launched from python, and to the right is extremely slow (almost unresponsible) launched from Qt/C++.

When I launch it from Qt/C++ in application output I get the warning:

• QObject::moveToThread: Current thread (0x275a700ce70) is not the object's thread (0x275a7032590).
• Cannot move to target thread (0x275a700ce70)

Please comment where maybe the reason of that...

Release mode. PySide2 and Qt/C++ are both 5.14.2. I use MSVC 2017 x64 compiler and Python 3.8.5 x64, Windows 10 x64

[JonB]

@Please_Help_me_D
Obviously the warnings are doubtless significant!
How do you do this " launched python module from Qt C++"?

[Please_Help_me_D]

@JonB I've found the problem. It was QApplication wich used to be created in both Qt/C++ and in Python Module. After I commented QApplication in Qt/C++ it works normally. Now the problem is that PySide2 widget looks different if it is launched from Qt/C++.

Here is the code maybe it will be useful for someone:

#undef slots
    #include <pybind11/embed.h> // everything needed for embedding
    #include <pybind11/pybind11.h>
    namespace py = pybind11;
#define slots

#include <QApplication>

int main(int argc, char *argv[])
{
//    QApplication a(argc, argv);
//    MainWindow w;
//    w.show();

    std::wstring pythonHome( L"C:/Anaconda3/envs/MyEnv38" );
    Py_SetPythonHome(pythonHome.c_str());

    py::scoped_interpreter guard{}; // start the interpreter and keep it alive

    py::list path = py::module::import("sys").attr("path");
    path.append("C:/las_reader");

//   py::eval_file("C:/lasreader.py"); // python module launcher via pybind

/* standard python module launcher */
    PyObject *obj = Py_BuildValue("s", "C:/las_reader/lasreader.py");
    FILE *file = _Py_fopen_obj(obj, "r+");
    if(file != nullptr) {
        PyRun_SimpleFile(file, "C:/las_reader/lasreader.py");
    }

    return 0;
}

[Please_Help_me_D]

The problem that Python called from Qt/C++ changes the style of application can be solved by copying the folder styles from C:\Anaconda3\envs\MyEnv38\Library\plugins to your built .exe file.