Re: [SQLObject] Bool value of SelectResult

[michelts <mic...@gm...>]

No :), go ahead!

2006/9/26, Oleg Broytmann <ph...@ph...>:
> Hello! I am going to return to this discussion. I'd like to raise an
> exception in  __nonzero__(). Any argument against this?
>
> On Fri, May 19, 2006 at 12:41:11PM -0500, Ian Bicking wrote:
> > Oleg Broytmann wrote:
> > >On Fri, May 19, 2006 at 10:12:23AM -0500, Ian Bicking wrote:
> > >
> > >>It inherits __nonzero__ already (so SelectResults are always true), but
> > >>does not implement __len__.  Like I said, I really dislike those very
> > >>few instances where you might encounter objects you can't test an object
> > >>for truth, so I'm not very positive about that resolution.  But I don't
> > >>know, that's really the only way to keep people from introducing bugs
> > >>into their code, since it's so natural (but probably incorrect) to test
> > >>a SelectResult for truthfulness.
> > >
> > >
> > >   We have to choose among the following possibilities:
> > >
> > >1) implement __nonzero__() via count() and warn users that it's slow;
> > >2) completely forbid __nonzero__() by raising an exception;
> > >3) allow users to choose; write some classes that a user use to choose the
> > >   desired behavior.
> >
> > 1) No one will see our warning, unless we actually make it a warning,
> > which is annoying and might as well be an exception IMHO.
> >
> > 2) Also annoying.  You have to do more explicit tests then, like "is
> > None" to avoid triggering __nonzero__.
> >
> > 3) I hate choice, then no one knows what someone else's code is going to
> > be doing, help is harder to provide, etc.
> >
> >
> > I'm leaning toward 2, like:
> >
> > def __nonzero__(self):
> >     raise NotImplementedError(
> >         "To test if a SelectResult will produce any items, use
> > list(result) or result.count()")
> >
> >
> > I'm not sure if it's a big backward compatibility problem, as I suspect
> > it will reveal as many bugs as it does correct code that won't work.
> > The only nuisance will be a place where people expect None, 0, and/or
> > other false items, and are using the current behavior to distinguish
> > those from SelectResult.  That seems uncommon.  If they just expect
> > None, replace it with "is None".  If they expect None or empty
> > containers (like []), then treating SelectResult like a boolean is
> > probably an outstanding bug.
> >
> >
> > --
> > Ian Bicking  /  ia...@co...  /  http://blog.ianbicking.org
> Oleg.
> --
>      Oleg Broytmann            http://phd.pp.ru/            ph...@ph...
>            Programmers don't die, they just GOSUB without RETURN.
>
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-- 
Michel Thadeu Sabchuk
Curitiba - Brasil