[Python-ideas] Allow isinstance second argument to be a set of types

[Michael Foord]

On 7 July 2011 20:12, Antoine Pitrou <solipsis at pitrou.net> wrote:

> On Thu, 7 Jul 2011 15:08:54 -0400
> Mike Graham <mikegraham at gmail.com> wrote:
> > On Thu, Jul 7, 2011 at 1:43 PM, Antoine Pitrou <
> solipsis-xNDA5Wrcr86sTnJN9+BGXg at public.gmane.org> wrote:
> > > On Thu, 7 Jul 2011 13:22:33 -0400
> > > Jim Jewett <jimjjewett at gmail.com> wrote:
> > >> On Wed, Jul 6, 2011 at 7:35 PM, Benjamin Peterson <
> benjamin-+ZN9ApsXKcEdnm+yROfE0A at public.gmane.org> wrote:
> > >>
> > >> > class Evil(type):
> > >> >    def __iter__(self):
> > >> >        return range(42)
> > >>
> > >> > class Accomplice(metaclass=Evil):
> > >> >    pass
> > >>
> > >> ... leading to isinstance(x, 42) rather than isinstance(x, Evil) if
> > >> the iterable check is done too soon.
> > >
> > > In what way is that a problem?
> > > That you can trigger exceptions by writing malicious code doesn't sound
> > > like a particularly novel event ;)
> >
> > I think people are assuming that an iterable metaclass isn't
> > fundamentally wrong.
>
> Well, it does sound fundamentally useless!
>

I've used indexable types before. I've never created an iterable one, but it
isn't unthinkable. :-)

Michael


>
> Regards
>
> Antoine.
>
>
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