[Python-Dev] Things to Know About Super (original) (raw)

Phillip J. Eby pje at telecommunity.com
Thu Aug 28 17:30:39 CEST 2008

At 06:35 AM 8/28/2008 +0200, Michele Simionato wrote:

Multiple inheritance of metaclasses is perhaps the strongest use case for multiple inheritance, but is it strong enough? I mean, in real code how many times did I need that? I would not mind make life harder for gurus and simpler for application programmers.

Then you need to leave MI and co-operation the hell alone. Right now, an application programmer can mix metaclasses like this:

class FooBar(Foo, Bar):
   class __metaclass__(Foo.__class__, Bar.__class__): pass
      ...

Or, in 3.x:

class FooBarClass(Foo.__class__, Bar.__class__): pass

class FooBar(Foo, Bar, metaclass=FooBarClass):
   ...

Either way, this is useful in cases where Foo and Bar come from different frameworks. That's the only way to get such things to co-operate, in fact.

I do not think removing cooperation would be so bad in practice. In many practical cases, one could just write the metaclass by hand,

How is that making things easier for application programmers?

Maybe you would need to duplicate a couple of lines and/or to introduce an helper function,

...which then has to have an agreed-upon protocol that all metaclass authors have to follow... which we already have... but which you're proposing to get rid of... so we can re-invent it lots of times... in mutually incompatible ways. :)

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