Hi, I have defined the following: bigint* bigint_constructor(long_ l){ return new bigint(to_bigint(l)); } class_<bigint>("bigint") .def("__init__", make_constructor(bigint_constructor)) .... .... implicitly_convertible(); Now I want to have a implicit conversion from long_ to bigint. My original c++ class has no constructor with long_ but my python-bigint class. The compiler tries to find one on c++ bigint and doesn't find it. How should I use implicitly_convertible to reach my goal? Benjamin