None versus MISSING sentinel -- request for design feedback

[Ethan Furman]

Mel wrote:
> Steven D'Aprano wrote:
> 
>> Well yes, but None is an explicit missing value too. The question I have
>> is if I should support None as that value, or something else. Or if anyone
>> can put a good case for it, both, or neither and so something completely
>> different.
> 
> If it's any help, I think (some of?) the database interface packages already 
> do just that, returning None when they find NULL fields.

Indeed.  I'm adding Null support to my dbf package now, and while some 
of the return values (Logical, Date, DateTime, and probably Character) 
will have their own dedicated singletons (Null, NullDate, NullDateTime, 
NullChar -- which will all compare equal to None) the numeric values 
will be None... although, now that I've seen this thread, I'll add the 
ability to choose what the numeric Null is returned as.

~Ethan~