function add_py_path()
%% add SS lib & python path
    additon_path=[pwd,'/3rd/py_igl_sdf'];
    if count(py.sys.path,additon_path) == 0
         insert(py.sys.path,int32(0),additon_path);
    end
    fprintf ('\nAdded py_igl_sdf paths.\n') ;
end