Question

I have a C++ object that is the child of a virtual class, and I am trying to wrap in python. The file compiles, and I can import it into python, but when I try to call the function, I get an error:

In [3]: x
Out[3]: <beh.MappedBehaviourDomain at 0x23e7158>

//So, obviously the constructor is working (or at least thinks it is)

In [4]: x.subject_count()
---------------------------------------------------------------------------
ArgumentError                             Traceback (most recent call last)
/home/max/verk/btr-email/build/x86_64/bin/ipython in <module>()
----> 1 x.subject_count()

ArgumentError: Python argument types in
    BehaviourDomainWrap.subject_count(MappedBehaviourDomain)
did not match C++ signature:
    subject_count(BehaviourDomainWrap {lvalue})
    subject_count(BehaviourDomainWrap {lvalue})

I’m having a hard time understanding this error; this is my first time working with boost python and I don’t have much experience with C++. Here’s the relevant code:

// Instantiating class for use in boost python
struct BehaviourDomainWrap : BehaviourDomain, wrapper<BehaviourDomain>
{
    size_t subjectCount() const {
        return this->get_override("subjectCount")();
    // A bunch of other methods removed
}


BOOST_PYTHON_MODULE(beh) {

    class_<BehaviourDomainWrap, boost::noncopyable>("BehaviourDomainWrap")
        .def("subject_count", pure_virtual(& BehaviourDomainWrap::subjectCount))
    ;

    class_<MappedBehaviourDomain, bases<BehaviourDomainWrap> >
        ("MappedBehaviourDomain", init<std::string>())
    ;
}

What’s going wrong, and why?

Answer 1

I was passing in the wrapped version of the object rather than the base. I should have had:

class_<BehaviourDomainWrap, boost::noncopyable>("beh")
    .def("subject_count", pure_virtual(& BehaviourDomain::subjectCount))
;

class_<MappedBehaviourDomain, bases<BehaviourDomain> >
    ("mapped_beh", init<std::string>())
;