Question about 'None'

[Francis Girard]

Oops, I misunderstood what you said. I understood that it was now the case 
that objects of different types are not comparable by default whereas you 
meant it as a planned feature for version 3.

I really hope that it will indeed be the case for version 3.

Francis Girard

Le jeudi 27 Janvier 2005 21:29, Steven Bethard a écrit :
> Francis Girard wrote:
> > Le jeudi 27 Janvier 2005 20:16, Steven Bethard a écrit :
> >>flamesrock wrote:
> >>>The statement (1 > None) is false (or any other value above 0). Why is
> >>>this?
> >>
> >>What code are you executing?  I don't get this behavior at all:
> >>
> >>py> 100 > None
> >>True
> >>py> 1 > None
> >>True
> >>py> 0 > None
> >>True
> >>py> -1 > None
> >>True
> >>py> -100 > None
> >>True
> >
> > Wow ! What is it that are compared ? I think it's the references (i.e.
> > the adresses) that are compared. The "None" reference may map to the
> > physical 0x0 adress whereas 100 is internally interpreted as an object
> > for which the reference (i.e. address) exists and therefore greater than
> > 0x0.
> >
> > Am I interpreting correctly ?
>
> Actually, I believe None is special-cased to work like this.  From
> object.c:
>
> static int
> default_3way_compare(PyObject *v, PyObject *w)
> {
> 	...
> 	if (v->ob_type == w->ob_type) {
> 		...
> 		Py_uintptr_t vv = (Py_uintptr_t)v;
> 		Py_uintptr_t ww = (Py_uintptr_t)w;
> 		return (vv < ww) ? -1 : (vv > ww) ? 1 : 0;
> 	}
> 	...
> 	/* None is smaller than anything */
> 	if (v == Py_None)
> 		return -1;
> 	if (w == Py_None)
> 		return 1;
> 	...
> }
>
> So None being smaller than anything (except itself) is hard-coded into
> Python's compare routine.  My suspicion is that even if/when objects of
> different types are no longer comparable by default (as has been
> suggested for Python 3.0), None will still compare as smaller than
> anything...
>
> Steve