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

PJ Eby pje at telecommunity.com
Wed Jun 6 17:39:07 CEST 2012

On Wed, Jun 6, 2012 at 5:31 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

On Wed, Jun 6, 2012 at 5:09 PM, Nick Coghlan <ncoghlan at gmail.com> wrote: > 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.

Upgrading this warning to a fact: there's no way this topic can be given the consideration it deserves in the space of the next three weeks. I'll be changing the title of 422, spend more time discussing the problem (rather than leaping to a conclusion) and retargeting the PEP at 3.4. If you do decide to play around with monkeypatching buildclass, please make clear to any users that it's a temporary fix until something more robust and less implementation dependent can be devised for 3.4.

Ideally, I would actually implement it as a backport of the PEP... in which case I suppose making it part of the class creation machinery (vs. embedding it in type.call or some place like that) will make that process easier.

Again, as I said earlier, I'm talking about this now because there was related discussion now, not because I'm actively trying to port my libraries. At this point, I've only done a few "make this library usable from 3.x as-is" changes by user request, for some of my smaller libraries that were mostly there already (e.g. simplegeneric). -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20120606/7d4b0290/attachment.html>

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