[Python-Dev] new metaclass error condition checks

Thomas Wouters thomas at python.org
Fri Apr 20 15:56:02 CEST 2007

On 4/17/07, Jean-Paul Calderone <exarkun at divmod.com> wrote:
> I just noticed r53997 (from some unit tests it broke), which disallowed
> things
> like this:
>     class X(object):
>         def __repr__(self):
>             return "blah"
>     class Y(X, type):
>         pass
>     class Z:
>         __metaclass__ = Y
> Making X classic eliminates the TypeError, and is probably an acceptable
> fix
> in a lot of cases (at least as long as classic classes are available).  I
> wonder if the ability to override type special methods like this was
> considered
> when the change was made, though?

Probably not, or at least not consciously. I think the point is that 'type'
and its subclasses are special enough that this warrants a separate 'X' that
inherits from 'type' rather than 'object'. Reduced reusability, but how
badly does this affect you in the real world, really?

Thomas Wouters <thomas at python.org>

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