Mine

/usr/include/boost/python/def_visitor.hpp: In static member function &#8216;static void boost::python::def_visitor_access::visit(const V&, classT&) [with V = boost::python::def_visitor<boost::python::api::object>, classT = boost::python::class_<VersionSpec_wrapper, boost::noncopyable_::noncopyable, boost::python::detail::not_specified, boost::python::detail::not_specified>]&#8217;:
/usr/include/boost/python/def_visitor.hpp:67:   instantiated from &#8216;void boost::python::def_visitor<DerivedVisitor>::visit(classT&) const [with classT = boost::python::class_<VersionSpec_wrapper, boost::noncopyable_::noncopyable, boost::python::detail::not_specified, boost::python::detail::not_specified>, DerivedVisitor = boost::python::api::object]&#8217;
/usr/include/boost/python/class.hpp:225:   instantiated from &#8216;boost::python::class_<T, X1, X2, X3>& boost::python::class_<T, X1, X2, X3>::def(const boost::python::def_visitor<Derived>&) [with Derived = boost::python::api::object, W = VersionSpec_wrapper, X1 = boost::noncopyable_::noncopyable, X2 = boost::python::detail::not_specified, X3 = boost::python::detail::not_specified]&#8217;
version_spec.cc:57:   instantiated from here
/usr/include/boost/python/def_visitor.hpp:31: error: no matching function for call to &#8216;boost::python::api::object::visit(boost::python::class_<VersionSpec_wrapper, boost::noncopyable_::noncopyable, boost::python::detail::not_specified, boost::python::detail::not_specified>&) const&#8217;