Mostly for fun (but you never know if somebody wants to take this seriously), let me mention that Python 3.8 allows abusing the CALL_METHOD optimization to make a “method” call like obj.meth() behave differently from x = obj.meth; x(). So it is technically possible to define a special descriptor denominator such that q.denominator and q.denominator() both work. But that’s very much relying on internals of the CPython interpreter.