Embeding PySide/PyQt widget into Qt/C++ application

Question

I have a C++/Qt application which should have its GUI extensible with modules. Extending should be simple and versatile. I am just checking a concept - is it possible to have this main C++/Qt application that would execute a Python/PySide/PyQt script which would create a QWidget (or derived class) instance and embed this widget into the main C++/Qt application?

Is there any working snippet to demonstrate the feasibility of this task? I.e. how to create and embed the widget? How to pass signals between the application and the widget?

Answer 1

Here is adapted for QT5 version of Francois answer:

#include "Python.h"
#include <QApplication>
#include <QMainWindow>

#include <iostream>

class PythonQt
{

public:

  PythonQt()
  {
    Py_SetProgramName(L"/path/to/executable");
    Py_SetPythonHome(L"/path/to/python-home");
    Py_IgnoreEnvironmentFlag = true;
    Py_Initialize();

    std::string code =
        "import sys\n"
        "print(sys.path)\n"
        "from PySide2 import QtGui\n"
        "from PySide2 import QtWidgets\n"
        ""
        "all_widgets = QtWidgets.QApplication.instance().allWidgets()\n"
        "window = None\n"
        "for widget in all_widgets:\n"
        "    if str(widget.objectName()) == \"main_window\":\n"
        "      window = widget\n"
        "      break\n"
        ""
        "def message_box():\n"
        "    QtWidgets.QMessageBox.information(None, 'Test', 'Hello!', \
                      QtWidgets.QMessageBox.Ok)\n"
        "    QtWidgets.QApplication.instance().quit()\n"
        ""
        "button = QtWidgets.QPushButton('Press Me')\n"
        "button.clicked.connect(message_box)\n"
        "window.setCentralWidget(button)\n"
        "window.move(600, 300)\n"
        "window.show()";

    PyRun_SimpleString(code.c_str());
  }

};

int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  QMainWindow win;
  win.setObjectName("main_window");

  PythonQt python_code;

  a.exec();
}

Answer 2

This question is a bit old, but in case someone else is face the same issue, I will try to give a useful answer.

I think it's possible. In the following example, I create a QApplication and QMainWindow in c++, embed a python interpreter, and then, on the python side, I create a QPushButton which I add to the main window.

Try this out:

#include <QApplication>
#include <QMainWindow>

#include <iostream>
#include "Python.h"

class PythonQt
{

public:

  PythonQt()
  {
    char name[] = "test";
    Py_SetProgramName(name);
    Py_Initialize();

    std::string code =
        "from PySide import QtGui\n"
        ""
        "all_widgets = QtGui.QApplication.instance().allWidgets()\n"
        "window = None\n"
        "for widget in all_widgets:\n"
        "    if str(widget.objectName()) == \"main_window\":\n"
        "      window = widget\n"
        "      break\n"
        ""
        "def message_box():\n"
        "    QtGui.QMessageBox.information(None, 'Test', 'Hello!', \ 
                      QtGui.QMessageBox.Ok)\n"
        "    QtGui.QApplication.instance().quit()\n"
        ""
        "button = QtGui.QPushButton('Press Me')\n"
        "button.clicked.connect(message_box)\n"
        "window.setCentralWidget(button)\n"
        "window.move(600, 300)\n"
        "window.show()";

    PyRun_SimpleString(code.c_str());
  }

};

int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  QMainWindow win;
  win.setObjectName("main_window");

  PythonQt python_code;

  a.exec();
}

The python script is written here in a string to have everything in a single file, but you could of course read it in from a .py file.

Object ownership could be an issue though, as shown in the link given by Trilarion.

Answer 3

I don't think this is possible. PySide/PyQt are wrappers around C++/Qt. That means you create C++ objects and Python wrapper objects and somehow the wrapper objects kind of refer to the C++ objects. This works one way as far as I know.

But you want the other way. Basically a wrapper around Python objects (which themselves are wrappers around C++ objects) to use in C++. I don't think PySide/PyQt are ready for thise. However it is possible to embed Python in other languages.

Also see How to shoot yourself in the foot. about the pitfalls of communication between C++/Qt and Python.