Hello, It's my first mail on this maillist. I started to upgrade a package for python 3.7, 3.8, 3.9 (linux and windows): vpython-wx. One file gives me some problems num_util.hpp My context: ubuntu 20.04: boost 1.71 python3.7 windows 10: boost 1.75 python3.7, 3.8, 3.9 I want to create a double_array class: Original version --------------------- namespace cvisual { namespace python { using boost::python::numeric::array; class double_array : public array { public: explicit double_array( const boost::python::handle<>& h ) : array(h) {} }; array makeNum(npy_intp n, NPY_TYPES t =NPY_DOUBLE); New version ----------------- namespace cvisual { namespace python { using boost::python::numpy::ndarray; class double_array : public ndarray { public: explicit double_array( const boost::python::handle<>& h ) : ndarray(h) {} }; ndarray makeNum(npy_intp n, NPY_TYPES t =NPY_DOUBLE); error message with VC2019 community error conversion 'const boost::python::handle<PyObject>' in 'boost::python::detail::borrowed_reference' error message with gcc 9.3 no matching function for call to ‘boost::python::numpy::ndarray::ndarray(const boost::python::handle<>&)’ Thanks a lot for your help. Philippe DALET Laboratoire de Physique Lyp Champollion, Figeac FRANCE