"0 in [True,False]" returns True

[bonono at gmail.com]

Steve Holden wrote:
> >>It would be somewhat more self-documenting, but why not just use one
> >>name to indicate the state and another, only meaningful in certain
> >>states, to indicate the callback?
> >
> >
> > Why should I do that? Checking the type of a variable is conceptually
> > no different form testing set membership. So what I did, was just
> > bringing two disjoint sets togther and working with a variable from
> > that union. This is all in all a rather simple mathematical idea.
> > And I don't see why I should put certain information into a seperate
> > variable. It makes as much sense as working with numbers and using
> > a seperate variable to store whether a particular number is postive,
> > even or has some other characteristic. You don't seperate information
> > you can easily acquire from the variable itself. So why should I
> > seperate this information that is aquired just as easily?
> >
>
> Well, as you might argue, I'm not tryng to effect a change in your
> behaviour, I'm simply trying to point out how it could be made more
> rational.
>
What would be the difference in his usage and allowing Null in a RDBMS
column ? Or return NaN instead of raising exception for numeric
functions ?