Question

i have written a library with some classes that make use of qt object such as QVector, QColor etc, without inheriting from them. Now I would like to make these objects (partially) available to python. I first tried SIP, but this is so poorly documented that I can’t even build the example. Now I am trying boost.python, which works fine for standard c++ classes.

However, once I start to include Qt stuff, it still compiles, but fails to import to python. Here is a minimal example:

testclass.h

#include <QDebug>
#include <QVector>
#include <QColor>

class testclass
{
public:
    testclass();
    const char* output();
    QVector<double> & data();
    static int x(){return 1;}
    QColor * c();

private:
    QVector<double> v;
};
struct stat;

testclass.cpp

#include "testclass.h"

testclass::testclass()
{

}

const char* testclass::output()
{
    qDebug() << "string";
    return "hello";
}

QVector< double >& testclass::data()
{
    return v;
}

QColor* testclass::c()
{
    return new QColor();
}

testclassBoost.cpp

#include "testclass.h"
#include <boost/python.hpp>

using namespace boost::python;

BOOST_PYTHON_MODULE(libtestclass)
{
    // Create the Python type object for our extension class and define __init__ function.
    class_<testclass>("testclass", init<>())
    .def("output", &testclass::output)  // Add a regular member function.
    ;
}

CMakeList.txt

project(boostpythontest)
cmake_minimum_required(VERSION 2.8)
find_package(Qt4 REQUIRED)

FIND_PACKAGE(Boost 1.45.0)
IF(Boost_FOUND)
  SET(Boost_USE_STATIC_LIBS OFF)
  SET(Boost_USE_MULTITHREADED ON)
  SET(Boost_USE_STATIC_RUNTIME OFF)
  FIND_PACKAGE(Boost 1.45.0 COMPONENTS python)
ELSEIF(NOT Boost_FOUND)
  MESSAGE(FATAL_ERROR "Unable to find correct Boost version. Did you set BOOST_ROOT?")
ENDIF()

include_directories(${QT_INCLUDES} ${CMAKE_CURRENT_BINARY_DIR} ${Boost_INCLUDE_DIRS} "/usr/include/python2.7")


set(SRCS
  testclass.cpp
  testclassBoost.cpp
)

add_library(testclass SHARED ${SRCS})

target_link_libraries(testclass ${Boost_LIBRARIES} ${QT_QTCORE_LIBRARY})

now trying to import the resulting library results in the following error:

Python 2.7.2 (default, Jun 27 2011, 14:59:25) 
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import libtestclass
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: ./libtestclass.so: undefined symbol: _ZN6QColor10invalidateEv

Interestingly, some qt classes are not problematic. Without the function c() it works fine (no problem with the QVector). What can I do to make this work? I do not intend to use any functions with qt stuff in python, but I would like to use qt in the c++ only part of the library.

Answer 1

You need QtGui for QColor, not just QtCore.