wrap std::vector<pointer*> in boost.python

Question

From my research it seems not very trivial to wrap std::vector that holds pointer types. For example:

std::vector<GameObject*>

I've looked at boost python vector_index_suite but it just gives me the runtime error:

TypeError: No to_python (by-value) converter found for C++ type: GameObject*

I have already exposed GameObject:

class_<GameObject>("GameObject") ...

So it have come to my understanding it's not possible with an out of the box solution. I have to do some kind of wrapper? Could someone just help me out where I should start?

jkp · Accepted Answer · 2012-04-02 16:51:34Z

2

The way to fix this is to explicitly state that your class wrapper applies to the pointer type as well.

class_<GameObject, GameObject*>("GameObject") ...

answered Apr 2, 2012 at 16:51

jkp

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Jan-Philip Loos · Accepted Answer · 2013-02-02 03:34:47Z

Can't comment @jkp but his hint did the trick for me. My minimalistic case:

RenderWorld.h

class RenderWorld {
    public:
        ...
        void addEntity(RenderEntity* entity) {entities.push_back(entity);};
        std::vector<RenderEntity*> getEntities(void) {return entities;};
    private:
        std::vector<RenderEntity*> entities;
 };

RenderEntity.h

 class RenderEntity {
     public:
         int getID(void) {return 42;};
 };

python-exportage.py.h (compiles to exported.pyd)

BOOST_PYTHON_MODULE(exported)
{
    class_<RenderWorld>("RenderWorld")
        .def("addEntity", &RenderWorld::addEntity)
        .def("getEntities", &RenderWorld::getEntities)
    ;

    class_<RenderEntity, RenderEntity*>("RenderEntity")
        .def("getID", &RenderEntity::getID)
    ;

    class_<std::vector<RenderEntity*> >("PyVec")
         .def(boost::python::vector_indexing_suite<std::vector<RenderEntity*> >())
    ;
}

my python session:

>>> import exported
>>> world = exported.RenderWorld()
>>> world
<exported.RenderWorld object at 0x00000000024A0E58>
>>> e1 = exported.RenderEntity()
>>> e1
<exported.RenderEntity object at 0x000000000284DF48>
>>> e1.getID()
42
>>> world.addEntity(e1)
>>> world.getEntities()
<exported.PyVec object at 0x000000000234B1B0>  
>>> world.getEntities()[0]
<exported.RenderEntity object at 0x0000000002441F50>
>>> world.getEntities()[0].getID()
42
>>> e1 == world.getEntities()[0]
False

Notable: The RenderEntity* will be wrapped in an other object. Look at these addresses and the last check. It's logical in a c++ perspective, but not in the python domain.

c++

Aleksey Vitebskiy · Accepted Answer · 2011-07-27 18:45:44Z

0

You have to also wrap your GameObject class. It won't work until you have a Python wrapper for the member object. If you don't want to expose members of the class, you can omit them, and just have an opaque object.

Also, boost::python works really well with shared pointers. This gives you an added benefit of safe memory handling. Any chance you can change std::vector<GameObject*> to std::vector<boost::shared_ptr<GameObject> >? This will work much better.

answered Jul 27, 2011 at 18:45

Aleksey Vitebskiy

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1 Comment

mrmclovin Over a year ago

Thanks for the answer, Yes, I have already exposed the GameObject with boost.python. It still doesn't work with vector<GameObject*>. I can't implement shared_ptr right now. Do you have an other suggestion how I can export the vector class?

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