I have a short example below which demonstrates and issue I'm having. I have a base class, "Base", written in C++ and exposed via boost.python. I have class, "Derived", which is written in Python and derives from the C++ base. In addition, there is a simple C++ function "func" which takes a Base* as an argument. What I'd like to be able to do is take a copy of an instance of the derived class, within Python, and pass it into the C++ function. However, this yields an ArgumentError exception: Boost.Python.ArgumentError: Python argument types in MyModule.func(Derived) did not match C++ signature: func(boost::shared_ptr<Base>) So it would appear that in taking a copy of the instance using Python's "copy.copy", I'm losing the C++ portion of the object. What is the correct way to go about doing this, please? Here's the test case I'm using: ================ C++ ============ struct Base { Base(){} }; typedef boost::shared_ptr<Base> BasePtr; void func( BasePtr b ) { std::cerr << "func(" << b.get() << ")" << std::endl; } BOOST_PYTHON_MODULE(MyModule) { class_<Base, BasePtr>("Base", no_init) .def(init<>()) ; def("func", func); } ================ Python ============ import copy from MyModule import * class Derived(Base): pass b = Base() func(b) d = Derived() func(d) d_copy = copy.copy(d) func(d_copy) ============ Example output ============== func(0x9db3500) func(0x9d76b20) Traceback (most recent call last): File "test.py", line 15, in <module> func(d_copy) Boost.Python.ArgumentError: Python argument types in MyModule.func(Derived) did not match C++ signature: func(boost::shared_ptr<Base>) Thanks in advance, Mark