On 5/2/06, Bill Birch <[EMAIL PROTECTED]> wrote: > On Tue, 2 May 2006 12:36 am, Guido van Rossum wrote: > > This has usually been solved by creating a non-meta class whose only > > purpose is to introduce the new metaclass. You'd write > > > > class TheLarch(KindsOfTrees, deciduous): ... > > > > and the metaclass would be called KindsOfTreesMeta. > > > > (Of course you could come up with a different naming convention.) > > > Sorry, but the reader has nothing to indicate that TheLarch is a different > _kind_ of class. It's no fair! Too much magic. It's hard to "recognize > different types of class from quite a long way away" with this. ;-)
Too bad (you're new to Python right?). The metaclass is inherited anyway, so this is not a new issure, and in practice it's not a problem -- you can usually tell from what the base class is, or from naming conventions, etc. > KindsOfTrees is a bad example of a meta-class. A better > example is a metaclass which behaves very differently from > normal classes. Consider a metaclass which does not allow methods: > > ----------------------struct.py-------------------------- > class StructMeta > ... > class Struct: > __metaclass__ = StructMeta > ... > -------------------------snip----------------------------- > from struct import * > class Person(Struct): > > To someone reading the second file this reads "Person inherits from struct". > Which of course it does not, because Struct is a devious hook to pull > in a different metaclass. What if StructMeta does not allow > inheritance? Then it'll be a run-time error at class definition time. This is how metaclasses work; better get used to it. I can't imagine how painful it would be if the metaclass *weren't* inherited -- lots of boilerplate all over. Please research the history of metaclasses in Python (and in general) before making your next post. -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
