Mailman 3 September 2011 - Cplusplus-sig

How can I pass derived Python instances to C++?
by James Amundson Sept. 8, 2011

Sept. 8, 2011

I would like to be able to create a Python class derived from a C++ class, then pass a instance of the Python class back to C++. It isn't clear to me if there is an easy way to do this. Here is a simple example of what I wish worked, but doesn't: C++ side: #include <boost/python.hpp> #include <iostream> class Foo { public: Foo(){}; virtual void doit(){std::cout << "doing it Foo style\n";}; }; void foodoer(Foo & foo) { foo.doit(); } using namespace boost::python; BOOST_PYTHON_MODULE(foo) { class_<Foo >("Foo", init<>()) .def("doit", &Foo::doit); def("foodoer", foodoer); } Python side: import foo class Bar(foo.Foo): def __init__(self): pass def doit(self): print "doing it bar style" f = foo.Foo() # next line works foo.foodoer(f) b = Bar() # next line does not work foo.foodoer(b) Does anyone have any advice for me? Thanks, Jim Amundson

2 2

Dynamic Cast failed over multiple modules
by Holger Brandsmeier Sept. 8, 2011

Sept. 8, 2011

Dear List, when I use dynamic cast from two boost modules on a class with "vague linkage", in my real use case a template in the simplified example I show you a class which is declared inline, then the dynamic cast fails in the second module. So when I call the code from python from the first module (in which the Vertex object has been created), then the dynamic cast succeeds: "calling performTest(m) ... I am a Vertex" but when I do the same from the other module, then I get "calling performTest2(m) ... dynamic cast failed, I got the object: I am a Vertex" I attached a very simple example in the files: bugDynamicCastSimplified.h (declares the Classes VerboseObject, Vertex and Mesh) bugDynamicCastPy.cpp (first boost module) bugDynamicCast2Py.cpp (second boost module) The problem dissapears without the vague linkage, e.g. when you define REMOVE_INLINE_DEFINITION in the code. This is not a very nice option for me, as in my real use case Vertex is a template, and this would force me to initialize it for each type. My gcc is: > g++ --version g++ (Gentoo 4.4.5 p1.2, pie-0.4.5) 4.4.5 And I am building the project with cmake (not boost). I read the FAQ entry at http://gcc.gnu.org/faq.html#dso and added "-Wl,-E" to CMAKE_SHARED_LINKER_FLAGS. About the RTLD_GLOBAL flag for dlopen, I don't know how python handles this. Do you have any ideas how to solve this? Or is this simply not possible with python? -Holger

2 2

Re: [C++-sig] Build Errors Making the "quickstart" Demo Project
by Paul Kroitor Sept. 8, 2011

Sept. 8, 2011

Hi, thanks for your reply. Yes, you are correct that "our attempts to build and/or use stock BPL is failing when building the quickstart demo". The boost build completes normally (but doesn't show any messages about running any tests) and specifies strings to add to the LIB and INCLUDE paths. At that point we simply CD to the quickstart sample directory and run "B2". This second build fails with a compiler error about an ambiguous call to an overloaded function. Is there something else that needs to be set? My understanding was that the earlier instructions for setting up the environment (bootstrap, user-config.jam) set up the environment for building both boost (which worked) and quickstart (which didn't). Here is the complete sequence: ............................................ C:\Boost\boost_1_47_0>.\b2 Building the Boost C++ Libraries. Performing configuration checks - has_icu builds : no warning: Graph library does not contain MPI-based parallel components. note: to enable them, add "using mpi ;" to your user-config.jam - ../config//has_gcc_visibility builds : no - ../config//has_long_double_support builds : yes warning: skipping optional Message Passing Interface (MPI) library. note: to enable MPI support, add "using mpi ;" to user-config.jam. note: to suppress this message, pass "--without-mpi" to bjam. note: otherwise, you can safely ignore this message. Component configuration: - chrono : building - date_time : building - exception : building - filesystem : building - graph : building - graph_parallel : building - iostreams : building - math : building - mpi : building - program_options : building - python : building - random : building - regex : building - serialization : building - signals : building - system : building - test : building - thread : building - wave : building ...patience... ...patience... ...patience... ...patience... ...found 7688 targets... The Boost C++ Libraries were successfully built! The following directory should be added to compiler include paths: C:/Boost/boost_1_47_0 The following directory should be added to linker library paths: C:\Boost\boost_1_47_0\stage\lib C:\Boost\boost_1_47_0>set include Environment variable include not defined C:\Boost\boost_1_47_0>set include=C:\Boost\Boost_1_47_0 C:\Boost\boost_1_47_0>set lib Environment variable lib not defined C:\Boost\boost_1_47_0>set lib=C:\Boost\boost_1_47_0\stage\lib C:\Boost\boost_1_47_0>cd libs\python\example\quickstart C:\Boost\boost_1_47_0\libs\python\example\quickstart>path %path%;c:\boost\boost_ 1_47_0 C:\Boost\boost_1_47_0\libs\python\example\quickstart>b2 ...patience... ...patience... ...found 1603 targets... ...updating 3 targets... compile-c-c++ bin\msvc-10.0\debug\threading-multi\embedding.obj embedding.cpp embedding.cpp(39) : error C2668: 'std::basic_string<_Elem,_Traits,_Ax>::basic_st ring' : ambiguous call to overloaded function with [ _Elem=char, _Traits=std::char_traits<char>, _Ax=std::allocator<char> ] c:\Program Files\Microsoft Visual Studio 10.0\VC\INCLUDE\xstring(700): c ould be 'std::basic_string<_Elem,_Traits,_Ax>::basic_string(std::basic_string<_E lem,_Traits,_Ax> &&)' with [ _Elem=char, _Traits=std::char_traits<char>, _Ax=std::allocator<char> ] c:\Program Files\Microsoft Visual Studio 10.0\VC\INCLUDE\xstring(590): o r 'std::basic_string<_Elem,_Traits,_Ax>::basic_string(const _Elem *)' with [ _Elem=char, _Traits=std::char_traits<char>, _Ax=std::allocator<char> ] while trying to match the argument list '(boost::python::detail::method_ result)' embedding.cpp(56) : error C2065: 'initembedded_hello' : undeclared identifier call "c:\Program Files\Microsoft Visual Studio 10.0\VC\vcvarsall.bat" x86 >n ul cl /Zm800 -nologo @"bin\msvc-10.0\debug\threading-multi\embedding.obj.rsp" ...failed compile-c-c++ bin\msvc-10.0\debug\threading-multi\embedding.obj... ...skipped <pbin\msvc-10.0\debug\threading-multi>embedding.exe for lack of <pbin \msvc-10.0\debug\threading-multi>embedding.obj... ...skipped <pbin\msvc-10.0\debug\threading-multi>embedding.pdb for lack of <pbin \msvc-10.0\debug\threading-multi>embedding.obj... ...failed updating 1 target... ...skipped 2 targets... ...................................... Am I missing something? _____________________________________________________ If I am understanding you correctly, your attempts to build and/or use stock BPL is failing when building the quickstart demo? If so, there is surely some issue with your build environment as Boost runs a series of automated regression tests which catch build failures. If I'm not right in understanding you correctly, please do explain further. Niall On 6 Sep 2011 at 14:01, Paul Kroitor wrote: > Hello all, > > > > We are adding a python scripting layer on top of an existing largish > C++ app, and are hoping to use Boost.Python to accomplish this. So > far, it's hasn't been going very smoothly, but I think we are nearly > to the point of getting the demo program to compile. > > > > For the most part, we are following the instructions here: > > http://www.boost.org/doc/libs/1_47_0/libs/python/doc/building.html > > > > but have also had to use hints from here > > http://stackoverflow.com/questions/2629421/how-to-use-boost-in-visual- > st > udio-2010 > > and several other forums to get as far as we have (who / where should > we report manual errors to?). > > > > I don't think we are doing anything non-standard - we certainly aren't > trying to - but perhaps some of the issues we are seeing come from > using Python 3.2. To complete the list, we are also using MSVC 10.0 > SP1 and Boost 1.47 on Windows 7 32-bit platform. > > > > Currently, we are trying to get the "quickstart" example working and > are stuck on an error in the build of "embedding.cpp": > > > > (note that for clarity I've rerun the build a second time so that it > is only trying to build the failed modules) > > > > ........................................................................ > ............... > > > > C:\Boost\boost_1_47_0\libs\python\example\quickstart>b2 > > ...patience... > > ...patience... > > ...found 1603 targets... > > ...updating 3 targets... > > compile-c-c++ bin\msvc-10.0\debug\threading-multi\embedding.obj > > embedding.cpp > > embedding.cpp(39) : error C2668: > 'std::basic_string<_Elem,_Traits,_Ax>::basic_st > > ring' : ambiguous call to overloaded function > > with > > [ > > _Elem=char, > > _Traits=std::char_traits<char>, > > _Ax=std::allocator<char> > > ] > > c:\Program Files\Microsoft Visual Studio > 10.0\VC\INCLUDE\xstring(700): c > > ould be > 'std::basic_string<_Elem,_Traits,_Ax>::basic_string(std::basic_string< > _E > > lem,_Traits,_Ax> &&)' > > with > > [ > > _Elem=char, > > _Traits=std::char_traits<char>, > > _Ax=std::allocator<char> > > ] > > c:\Program Files\Microsoft Visual Studio > 10.0\VC\INCLUDE\xstring(590): o > > r 'std::basic_string<_Elem,_Traits,_Ax>::basic_string(const _Elem > *)' > > with > > [ > > _Elem=char, > > _Traits=std::char_traits<char>, > > _Ax=std::allocator<char> > > ] > > while trying to match the argument list > '(boost::python::detail::method_ > > result)' > > embedding.cpp(56) : error C2065: 'initembedded_hello' : undeclared > identifier > > > > call "c:\Program Files\Microsoft Visual Studio > 10.0\VC\vcvarsall.bat" x86 >n > > ul > > cl /Zm800 -nologo > @"bin\msvc-10.0\debug\threading-multi\embedding.obj.rsp" > > > > ...failed compile-c-c++ > bin\msvc-10.0\debug\threading-multi\embedding.obj... > > ...skipped <pbin\msvc-10.0\debug\threading-multi>embedding.exe for > lack of <pbin > > \msvc-10.0\debug\threading-multi>embedding.obj... > > ...skipped <pbin\msvc-10.0\debug\threading-multi>embedding.pdb for > lack of <pbin > > \msvc-10.0\debug\threading-multi>embedding.obj... > > ...failed updating 1 target... > > ...skipped 2 targets... > > > > ........................................................................ > ............... > > > > With all the templates and overloads, this is getting too technical > for to solve here. I am hoping someone here will recognize this error > or understand what's causing it. > > > > Thanks in advance for any help or guidance anyone is able to give. > > Paul Kroitor > >

2 1

Build Errors Making the "quickstart" Demo Project
by Paul Kroitor Sept. 7, 2011

Sept. 7, 2011

Hello all, We are adding a python scripting layer on top of an existing largish C++ app, and are hoping to use Boost.Python to accomplish this. So far, it's hasn't been going very smoothly, but I think we are nearly to the point of getting the demo program to compile. For the most part, we are following the instructions here: http://www.boost.org/doc/libs/1_47_0/libs/python/doc/building.html but have also had to use hints from here http://stackoverflow.com/questions/2629421/how-to-use-boost-in-visual-st udio-2010 and several other forums to get as far as we have (who / where should we report manual errors to?). I don't think we are doing anything non-standard - we certainly aren't trying to - but perhaps some of the issues we are seeing come from using Python 3.2. To complete the list, we are also using MSVC 10.0 SP1 and Boost 1.47 on Windows 7 32-bit platform. Currently, we are trying to get the "quickstart" example working and are stuck on an error in the build of "embedding.cpp": (note that for clarity I've rerun the build a second time so that it is only trying to build the failed modules) ........................................................................ ............... C:\Boost\boost_1_47_0\libs\python\example\quickstart>b2 ...patience... ...patience... ...found 1603 targets... ...updating 3 targets... compile-c-c++ bin\msvc-10.0\debug\threading-multi\embedding.obj embedding.cpp embedding.cpp(39) : error C2668: 'std::basic_string<_Elem,_Traits,_Ax>::basic_st ring' : ambiguous call to overloaded function with [ _Elem=char, _Traits=std::char_traits<char>, _Ax=std::allocator<char> ] c:\Program Files\Microsoft Visual Studio 10.0\VC\INCLUDE\xstring(700): c ould be 'std::basic_string<_Elem,_Traits,_Ax>::basic_string(std::basic_string<_E lem,_Traits,_Ax> &&)' with [ _Elem=char, _Traits=std::char_traits<char>, _Ax=std::allocator<char> ] c:\Program Files\Microsoft Visual Studio 10.0\VC\INCLUDE\xstring(590): o r 'std::basic_string<_Elem,_Traits,_Ax>::basic_string(const _Elem *)' with [ _Elem=char, _Traits=std::char_traits<char>, _Ax=std::allocator<char> ] while trying to match the argument list '(boost::python::detail::method_ result)' embedding.cpp(56) : error C2065: 'initembedded_hello' : undeclared identifier call "c:\Program Files\Microsoft Visual Studio 10.0\VC\vcvarsall.bat" x86 >n ul cl /Zm800 -nologo @"bin\msvc-10.0\debug\threading-multi\embedding.obj.rsp" ...failed compile-c-c++ bin\msvc-10.0\debug\threading-multi\embedding.obj... ...skipped <pbin\msvc-10.0\debug\threading-multi>embedding.exe for lack of <pbin \msvc-10.0\debug\threading-multi>embedding.obj... ...skipped <pbin\msvc-10.0\debug\threading-multi>embedding.pdb for lack of <pbin \msvc-10.0\debug\threading-multi>embedding.obj... ...failed updating 1 target... ...skipped 2 targets... ........................................................................ ............... With all the templates and overloads, this is getting too technical for to solve here. I am hoping someone here will recognize this error or understand what's causing it. Thanks in advance for any help or guidance anyone is able to give. Paul Kroitor

2 1

pickle the unpickleable
by Neal Becker Sept. 6, 2011

Sept. 6, 2011

I have a pickling problem I suspect is just not possible to solve. I have some wrappers around boost::random objects. There is a rng object, which is a single underlying mersenne twister. There are various distributions. For example, uniform_real. Each uniform_real holds a reference to the single, external mt object. I don't think there's any way to unpickle several instance of uniform_real so that their references to the (shared) mt object get correctly restored. Imagine something like this: class mt; struct uniform_real { mt & _mt; uniform_real (mt &, min, max) ... }; When unpickled, the internal _mt states are saved and restored correctly, but 2 instances of uniform_real will not share a reference to a single mt object, they each have their own copy which starts with a copy of the same state (no good).

2 2

copy constructors and multiple instances
by Josh Stratton Sept. 3, 2011

Sept. 3, 2011

In my particular scene I have a Scene class, which operates as kind of a context for my operations and holds all the meshes in the scene. I send my scene down to the python side so import methods will import into the containers in the scene object. For example, addMeshFromFile(scene, fileName) which puts the data from the file into the scene object. However, if the scene object isn't be returned, it seems I'm just copying the scene object (which might be memory expensive), adding the data to the copy, and throwing the copy away as I don't return it and it doesn't affect my original scene object in C++ that I passed in. I assume this is a fairly common problem and I need to rework my API somehow like providing a more robust copy constructor that does a shallow copy of my data containers. Still, I might have to reorganize it so I'm not passing my scene to python. If an object is copied every time, I think that might be memory prohibitive. I'm including my current source from github. // header file handling my scene and it's data https://github.com/strattonbrazil/Sunshine/blob/master/src/scene.h // functions for creating the bindings to python https://github.com/strattonbrazil/Sunshine/blob/master/src/python_bindings.… // python file which reads a file and adds it to the scene https://github.com/strattonbrazil/Sunshine/blob/master/src/objImporter.py Do I need to change need to change my copy constructor to do a more shallow copy? Maybe change my internal scene objects to pointers? Would this alleviate the memory issue?

4 13

sending a c++ class to a python function
by Josh Stratton Sept. 1, 2011

Sept. 1, 2011

I'm getting an error when I try to pass down my object that results in a seg fault. I've registered my class I'm sending down, but when I actually send it, my program exits at this line in the library right after I call the importFile() function... return call<obj>(get_managed_object(self, tag), BOOST_PP_ENUM_PARAMS_Z(1, N, a)); // here's the class I'm trying to send down class Scene { public: MeshP mesh(int key); void clearScene(); CameraP createCamera(QString name); MeshP createMesh(QString name); void setMesh(int meshKey, MeshP mesh) { _meshes[meshKey] = mesh; } QHashIterator<int, MeshP> meshes() { return QHashIterator<int,MeshP>(_meshes); } QHashIterator<int, CameraP> cameras() { return QHashIterator<int,CameraP>(_cameras); } CameraP fetchCamera(QString name); QList<QString> importExtensions(); void importFile(QString fileName); void evalPythonFile(QString fileName); Scene(); protected: int uniqueCameraKey(); int uniqueMeshKey(); QString uniqueName(QString prefix); private: QHash<int,MeshP> _meshes; QHash<int,CameraP> _cameras; //QHash<int,Light*> _lights; QSet<QString> _names; // PythonQtObjectPtr _context; object _pyMainModule; object _pyMainNamespace; public slots: void pythonStdOut(const QString &s) { std::cout << s.toStdString() << std::flush; } void pythonStdErr(const QString &s) { std::cout << s.toStdString() << std::flush; } }; // first I create the mapping, which I'm not sure is correct, trying to follow: http://misspent.wordpress.com/2009/09/27/how-to-write-boost-python-converte… struct SceneToPython { static PyObject* convert(Scene const& scene) { return boost::python::incref(boost::python::object(scene).ptr()); } }; // then I register it boost::python::to_python_converter<Scene,SceneToPython>(); // then I send it down from inside my Scene object try { object processFileFunc = _pyMainModule.attr("MeshImporter").attr("processFile"); processFileFunc(this, fileName); // seems to error here } catch (boost::python::error_already_set const &) { QString perror = parse_python_exception(); std::cerr << "Error in Python: " << perror.toStdString() << std::endl; } I'm not really sure what actually is wrong besides something being setup incorrectly. Do I need to make a python-to-C++ converter as well even if I'm not sending it back to C++? Or is my convert() function just improperly implemented? I wasn't sure how much I need to actually get it to map correctly. Thanks.

2 4