wrapper like Blob createBlob(const std::string data) { return Blob(data.str(),data.size()); } Can I pass this funktion to boost.python in a way, that I could be used as ctor? Something like this: class_<Blob>("Blob",init<>()) .def( ??? , createBlob ); and then from Python: data = "a string with data to be passed to the blob" blob = Blob(data) regards, Achim