Pass function reference with boost python

Question

I have such function in C++:

typedef boost::function<boost::shared_ptr<Object> (CL_DomElement*, std::string& desc)> Parser;
void registerParser(std::string type, Parser p);

// Later: exporting into python-module:
BOOST_PYTHON_MODULE(TypesManager)
{
    bp::def("RegisterParser", registerParser);
}

# Python code:
class TestObj(Object):
    @staticmethod
    def ParseTestObj(node, desc):
        pass

RegisterParser("test_obj", TestObj.ParseTestObj)

Object in python-code is exported class which is used in typedef (from c++ code).

Boost.Python.ArgumentError: Python argument types in
    RegisterParser(str, function)
did not match C++ signature:
    RegisterParser(TypesManager {lvalue}, std::string, boost::function<boost::shared_ptr<Object> ()(CL_DomElement*, std::string&)>)

What I do wrong?

Xeo · Accepted Answer · 2011-03-30 20:05:16Z

I don't believe Boost Python understands how to convert a python function to a boost::function object. What I would suggest is to use a proxy to take the python callable object and mimic the C++ interface. Quick example mock-up (untested, of course):

typedef boost::function<boost::shared_ptr<Object> (CL_DomElement*, std::string& desc)> Parser;
void registerParser(std::string type, Parser p);

struct ParserProxy
{
    bp::object callable;

    ParserProxy(bp::object callable)
    : callable(callable)
    { }

    boost::shared_ptr<Object> operator()(CL_DomElement* elem, std::string& desc)
    {
        bp::object obj = callable(elem, desc);
        return bp::extract<boost::shared_ptr<Object> >(obj);
    }
};

void registerParserByProxy(std::string type, bp::object callable)
{
    registerParser(type, ParserProxy(callable));
}

// Later: exporting into python-module:
BOOST_PYTHON_MODULE(TypesManager)
{
        bp::def("RegisterParser", registerParserByProxy);
}

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