On Aug 10, 5:27 pm, Eric Snow <ericsnowcurren...@gmail.com> wrote: > On Wed, Aug 10, 2011 at 8:33 AM, Fuzzyman <fuzzy...@gmail.com> wrote: > > On Aug 5, 12:29 pm, Ryan <heni...@yahoo.com> wrote: > >> In the context of descriptors, the __set__ method is not called for > >> class attribute access. __set__ is only > >> called to set the attribute on an instance instance of the owner class > >> to a new value, value. WHY? > > > It's an unfortunate asymmetry in the descriptor protocol. You can > > write "class descriptors" with behaviour on get, but not on set. > > > As others point out, metaclasses are an ugly way round this > > (particularly given that *basically* a class can only have one > > metaclass - so if you're inheriting from a class that already has a > > custom metaclass you can't use this technique). > > Keep in mind that you can still do something like this: > > class XMeta(Base.__class__): > "Customize here" > > class X(Base, metaclass=XMeta): > "Do your stuff." > > They you would put your descriptor hacking in XMeta and still take > advantage of the original metaclass.
Yeah, the way round the "more than one metaclass problem" is to have your new metaclass inherit from the first one. That's not a general purpose solution though. Michael -- http://voidspace.org.uk/ -- http://mail.python.org/mailman/listinfo/python-list
