[Python-Dev] Possible rough edges in Python 3 metaclasses (was Re: Language reference updated for metaclasses) (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Wed Jun 6 09:09:06 CEST 2012

On Wed, Jun 6, 2012 at 1:28 AM, PJ Eby <pje at telecommunity.com> wrote:

To be clear, what I specifically proposed (as I mentioned in an earlier thread) was simply to patch buildclass in order to restore the missing metaclass hook.  (Which, incidentally, would make ALL code using metaclass cross-version compatible between 2.x and 3.x: a potentially valuable thing in and of itself!)

As for metaclasses being hard to compose, PEP 422 is definitely a step in the right direction.  (Automatic metaclass combining is about the only thing that would improve it any further.)

Just as a warning, I doubt I'll be able to persuade enough people that this is a feature worth including in the short time left before 3.3 feature freeze. It may end up being necessary to publish metaclass and explicit decorator based variants (with their known limitations), with a view to gaining support for inclusion in 3.4.

Alternatively, if people can supply examples of "post-creation manipulation only" metaclasses that could be replaced with cleaner and more composable dynamic decorator based solutions, that could help make the PEP more compelling in the near term (perhaps compelling enough to make it into 3.3).

Cheers, Nick.

-- Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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