Question about 'None'

[Steven Bethard]

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