[Python-3000] __nonzero__ vs. __bool__
Brett Cannon
brett at python.org
Tue Nov 21 21:32:05 CET 2006
On 11/21/06, Walter Dörwald <walter at livinglogic.de> wrote:
>
> tomer filiba wrote:
> > patch updated
>
> You're fast! ;)
>
> AFAICT now we have the following problem: If
> Objects/typeobject.c::slot_nb_bool() falls back to using __len__(), the
> return value of __len__() must be a bool.
Why can't the fallback usage just pass the return value from __len__ to
bool() (forget the C function name) and return that result? It's just like
doing::
def bool(obj):
try:
return obj.__bool__()
except AttributeError:
return bool(len(obj))
-Brett
Servus,
> Walter
>
> > On 11/21/06, *Guido van Rossum* <guido at python.org
> > <mailto:guido at python.org>> wrote:
> >
> > I think it would set a good example if __bool__ was *required* to
> > return exactly True or False and no other object, not even int
> > instances equal to 0 or 1. Surely that can't be much of a burden.
> Feel
> > free to upload an improved patch.
> >
> > On 11/21/06, Walter Dörwald <walter at livinglogic.de
> > <mailto:walter at livinglogic.de>> wrote:
> > > Guido van Rossum wrote:
> > > > On 11/21/06, Ivan Krstić < krstic at solarsail.hcs.harvard.edu
> > <mailto:krstic at solarsail.hcs.harvard.edu>> wrote:
> > > >> Guido van Rossum wrote:
> > > >>> Can anyone help out evaluating this patch? If it has to wait
> > for me
> > > >>> it's gonna be a looooooong wait...
> > > >> Looks fine to me functionally, although it seems to
> > gratuitously retab
> > > >> some code that used to be aligned with tabstop 8 to a tabstop
> of 4.
> > > >
> > > > Thanks! I hope you meant "indentation level" instead of
> "tabstop".
> > > > Tomer, can you fix the indentation to be whatever's prevailing
> > in the
> > > > file you're editing?
> > >
> > > Another question is whether __bool__() should be allowed to return
> an
> > > int (or any other object), or if it *must* be a bool. (The patch
> > > currently allows ints). What if __bool__() returns subclasses of
> int,
> > > that overwrite __bool__() themself?
> > >
> > > Servus,
> > > Walter
> > >
> > >
> >
> >
> > --
> > --Guido van Rossum (home page: http://www.python.org/~guido/)
> >
> >
>
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