[Python-ideas] A (meta)class algebra (original) (raw)

Antony Lee antony.lee at berkeley.edu
Fri Feb 13 18:27:56 CET 2015

While PEP422 is somewhat useful for heavy users of metaclasses (actually not necessarily so heavy; as mentioned in the thread you'll hit the problem as soon as you want to make e.g. a QObject also instance of another metaclass), I don't like it too much because it feels really ad hoc (adding yet another layer to the already complex class initialization machinery), whereas dynamically creating the sub-metaclass (inheriting from all the required classes) seems to be the "right" solution. In a sense, using an explicit and ad hoc mixer ("add") would be like saying that every class should know when it is part of a multiple inheritance chain, whereas the implicit ("multi_meta") mixer just relies on Python's MRO to do the right thing. Of course, best would be that the "multi_meta" step be directly implemented at the language level, and I agree that having to add it manually isn't too beautiful.

init_class could then simply be implemented as part of a normal metaclass, from which you could inherit without worrying about other metaclasses.

Antony

2015-02-13 5:27 GMT-08:00 Martin Teichmann <lkb.teichmann at gmail.com>:

Hi,

me too, I missed that PEP, and yes, it would certainly work for all my needs. In short words, the PEP reads: forget all that metaclass stuff, here comes the real solution. Maybe we can even abandon metaclasses altogether in Python 4, I think noone would shed a tear over them. But if the metaclass fans should win the battle, I would like my proposal included sometimes. Greetings Martin

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