On Fri, Nov 17, 2017 at 3:15 AM Nick Coghlan <ncogh...@gmail.com> wrote:
> On 17 November 2017 at 15:52, Steven D'Aprano <st...@pearwood.info> wrote: > > There's a lot of benefit to having a relatively simple, understandable > > algorithm for determining the MRO, as opposed to some sort of adaptive > > rule that will try to reorder classes according to potentially clashing > > constraints. If that means that some classes cannot go together in > > multiple inheritence because their MRO would be inconsistent, I think > > that's a price worth paying for not having to debug inheritence bugs > > caused by weirdly reordered MROs. > > I'll note that an interesting side effect of > https://www.python.org/dev/peps/pep-0560/#mro-entries will be to allow > folks to write: > > class MyCustomMRO: > def __init__(self, *bases): > self._resolved_bases = my_mro_resolver(bases) > def __mro_entries(self, orig_bases): > if len(orig_bases) > 1 or orig_bases[0] is not self: > raise TypeError("CustomMRO instance must be sole base > class") > return self._resolved_bases > > > class Z(MyCustomMRO(B, R)): > ... > > The custom MRO algorithm may then allow for use case specific hints to > handle situations that the default C3 resolver will reject as > inconsistent or ambiguous. (I'll also note that such a custom resolver > would be able to manufacture and inject synthetic metaclasses if > that's what someone decided they really wanted to do, by also > synthesising a custom base class to stick at the head of the list of > bases). > This is really cool! Like you said, this goes above and beyond what I was proposing. I guess my problem could be added as a motivation for PEP-560's __mro_entries__. (cc Ivan) > Cheers, > Nick. > > -- > Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ > > -- > > --- > You received this message because you are subscribed to a topic in the > Google Groups "python-ideas" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/python-ideas/T7YNKZmwW1c/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > python-ideas+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. >
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