first qt application launching a python script. with a segmentation fault, the second time the script is launched

Author: aoloe

qt-5-pyqt5/CMakeLists.txt

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+CMAKE_MINIMUM_REQUIRED(VERSION 3.4)
+
+PROJECT(sample)
+
+SET(CMAKE_CXX_STANDARD 14)
+
+set(CMAKE_INCLUDE_CURRENT_DIR ON)
+
+set(CMAKE_AUTOMOC ON)
+
+find_package(Qt5Widgets)
+
+set(PYBIND11_PYTHON_VERSION 3.4)
+
+FIND_PACKAGE(pybind11 CONFIG)
+
+ADD_DEFINITIONS(-DSCRIPTS_DIRECTORY="${CMAKE_SOURCE_DIR}")
+
+ADD_EXECUTABLE(sample
+    src/main.cpp
+    src/sample.cpp
+    src/mainwindow.cpp
+    src/scripter.cpp
+)
+
+target_link_libraries(sample
+    Qt5::Widgets
+    ${PYTHON_LIBRARIES}
+    pybind11::embed
+)
+
+project(sampleapi)
+pybind11_add_module(sampleapi src/scripterAPI.cpp)

qt-5-pyqt5/README.md

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+# c++ launches a Python script that loads a shared library module and sets a c++ variable
+
+- Create a `.so` module.
+- Call the Python script from the c++ code and pass a variable per reference.
+- The Python script loads the module and modify the variable.
+- The c++ code checks that the values has been modified
+
+~~~.sh
+$ mkdir build
+$ cmake -Dpybind11_DIR=/home/ale/bin/pybind11/share/cmake/pybind11 -DCMAKE_BUILD_TYPE=Debug ..
+$ make
+$ ./sample
+~~~
+
+For now, you have to copy the generated `fooapi.cpython-35m-x86_64-linux-gnu.so` file next to the python script.

qt-5-pyqt5/python/set-bar.py

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+import sampleapi
+
+print(foo_copy.bar)
+foo_copy.bar = 5
+print(foo_copy.bar)
+foo_ref.bar = 5
+

qt-5-pyqt5/src/main.cpp

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+#include <QDebug>
+
+#include "sample.h"
+#include "mainwindow.h"
+
+int main(int argc, char *argv[])
+{
+    Sample app(argc, argv);
+
+    MainWindow mainWin;
+    mainWin.show();
+
+    return app.exec();
+}

qt-5-pyqt5/src/mainwindow.cpp

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+#include <iostream>
+#include "mainwindow.h"
+#include "scripter.h"
+
+#include <QtWidgets>
+#include <QDebug>
+#include <QString>
+
+MainWindow::MainWindow()
+{
+    createActions();
+}
+
+void MainWindow::createActions()
+{
+    QMenu *fileMenu = menuBar()->addMenu(tr("&File"));
+    QAction *exitAct = fileMenu->addAction(tr("E&xit"), this, &QWidget::close);
+    exitAct->setShortcuts(QKeySequence::Quit);
+
+    QMenu *scriptMenu = menuBar()->addMenu(tr("&Script"));
+    QAction *runAct = scriptMenu->addAction(tr("&Run"), this, &MainWindow::scriptRun);
+
+    QMenu *helpMenu = menuBar()->addMenu(tr("&Help"));
+    QAction *aboutAct = helpMenu->addAction(tr("&About"), this, &MainWindow::about);
+    // add an help entry that responds to F1
+}
+
+void MainWindow::scriptRun()
+{
+	QString fileName = QFileDialog::getOpenFileName(this,
+		// tr("Open Image"), QStandardPaths::standardLocations(QStandardPaths::HomeLocation).last(), tr("Image Files (*.py *.png *.jpg *.bmp)"));
+		tr("Open Image"), SCRIPTS_DIRECTORY, tr("Image Files (*.py *.png *.jpg *.bmp)"));
+    qDebug() << "fileName" << fileName;
+    std::cout << "filename: " << fileName.toStdString() << std::endl;
+
+    Scripter scripter;
+    scripter.runFile(fileName.toStdString());
+}
+
+void MainWindow::about()
+{
+    QMessageBox::about(this, tr("About this sample"),
+        tr("This <i>Sample</i> creates a window with a menu bar."));
+}

qt-5-pyqt5/src/mainwindow.h

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+#ifndef MAINWINDOW_H
+#define MAINWINDOW_H
+
+#include <QMainWindow>
+
+class MainWindow : public QMainWindow
+{
+    Q_OBJECT
+public:
+    MainWindow();
+private slots:
+    void scriptRun();
+    void about();
+private:
+    void createActions();
+};
+#endif

qt-5-pyqt5/src/sample.cpp

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+#include "sample.h"
+
+#include <QDebug>
+
+Sample::Sample(int &argc, char *argv[]) :
+    QApplication(argc, argv)
+{
+    setApplicationName("Application Sample");
+    setApplicationVersion("0.1");
+}

qt-5-pyqt5/src/sample.h

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+#ifndef SAMPLE_H
+#define SAMPLE_H
+
+#include<QApplication>
+
+class Sample : public QApplication
+{
+    Q_OBJECT
+public:
+    explicit Sample(int &argc, char *argv[]);
+
+};
+#endif

qt-5-pyqt5/src/scripter.cpp

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+#include "scripter.h"
+#include "scripterAPI.h"
+
+using namespace pybind11::literals;
+
+void Scripter::runFile(std::string fileName)
+{
+	ScripterAPI foo1, foo2;
+
+	auto module = py::module::import("sampleapi");
+
+	auto locals = py::dict("foo_copy"_a=foo1, "foo_ref"_a=py::cast(foo2, py::return_value_policy::reference)); // foo1 by value, foo2 by reference
+
+    py::eval_file(fileName, py::globals(), locals);
+
+	assert(foo1.bar == 1);
+	assert(foo2.bar == 5);
+}

qt-5-pyqt5/src/scripter.h

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+#include <string>
+#include <QString>
+
+#undef slots // avoid conflicts between Python.h and Qt slots
+#include <pybind11/pybind11.h>
+#include <pybind11/embed.h>
+#define slots Q_SLOTS
+
+namespace py = pybind11;
+
+class Scripter
+{
+    public:
+        void runFile(std::string fileName);
+    private:
+        py::scoped_interpreter guard{}; // start the interpreter and keep it alive
+};