Maybe I got a small step further. I received a few advices from Jörg Budischewski:
Say, I define my IDL like this: interface Xcvxopt : com::sun::star::uno::XInterface { string lp( [in] sequence < sequence < long > > c, [out] sequence < sequence < long > > x); }; The Jörg suggested I define my Python method as: def lp(self, c, x): x = (1,2) return "test", x but whenever I try to invoke it from the spreadsheet as =lp(A1:A2,B1:B2) (and all sorts of variations) I get a #NAME? error, so it's like oocalc doesnt parse my Python add-in because of an error. I should mention that if I only have [in] fields in the IDL, then my add-in works fine. How else would I invoke it from the spreadsheet?