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I'm trying to expose my C++ Classes to Python using Boost.Python. Here is a simplyfied version of what i'm trying to do: I have a class A deriving from boost::noncopyable and a second class B with a method that takes a reference to A as an argument. class A : boost::noncopyable { /*...*/ }; class B { public: virtual void do_something(A& a) { /*...*/ } }; I'm exposing the classes as follows: /* Wrapper for B, so B can be extended in python */ struct BWrap : public B, wrapper<B> { void do_something(A &a) { if (override do_something = this->get_override("do_something")) { do_something(a); return; } else { B::do_something(a); } } void default_do_something(A& a) { this->B::do_something(a); } }; BOOST_PYTHON_MODULE(SomeModule) { class_<A, boost::noncopyable>("A"); class_<BWrap, boost::noncopyable>("B") .def("do_something", &B::do_something, &BWrap::default_do_something) ; } I extend B in python like this: test.py: import SomeModule class BDerived(SomeModule.B): def do_something(self, a): pass and call the extended B like this: try { py::object main = py::import("__main__"); \ py::object global(main.attr("__dict__")); \ py::object result = py::exec_file("test.py", global, global); \ py::object pluginClass = global["BDerived"]; \ py::object plugin_base = pluginClass(); \ B& plugin = py::extract<B&>(plugin_base) BOOST_EXTRACT_WORKAROUND; A a; B.do_something(a); } catch (py::error_already_set) { PyErr_Print(); } However this results in an error message: TypeError: No to_python (by-value) converter found for C++ type: A If A isn't derived from <

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