[Python-3000] ABC PEP isinstance issue Was: PEP 31XX: A Type Hierarchy for Numbers (and other algebraic entities)

Jean-Paul Calderone exarkun at divmod.com
Thu Apr 26 00:40:25 CEST 2007

On Wed, 25 Apr 2007 18:10:23 -0400, Jim Jewett <jimjjewett at gmail.com> wrote:
>The current ABC proposal is to use isinstance as the test; Jeffrey
>Yaskin's numbers PEP highlighted the weakness there with a concrete
>If you need to an abstraction less powerful than an existing ABC,
>you're out of luck; you can't just assert that the existing class is
>already sufficient, nor can you expect everyone else to use multiple

I'm sure everyone is already aware of the behavior of the classImplements
and directlyProvides functions available in zope.interface, which exactly
satisfy this use-case in the interface world.


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