On May 31, 4:11 pm, LittleGrasshopper <seattleha...@yahoo.com> wrote: > On May 31, 3:59 pm, Carl Banks <pavlovevide...@gmail.com> wrote: > > > > > On May 31, 3:52 pm, LittleGrasshopper <seattleha...@yahoo.com> wrote: > > > > This is some simple code which I got from Guido's paper on the > > > unification of classes and types, which Arnaud suggested to improve my > > > knowledge of metaclasses: > > > > class M1(type): > > > pass > > > class M2(M1): > > > pass > > > class M3(M2): > > > pass > > > class C1: > > > __metaclass__ = M1 > > > class C2(C1): > > > __metaclass__ = M2 > > > class C3(C1, C2): > > > __metaclass__ = M3 > > > > It is failing when processing C3: > > > Traceback (most recent call last): > > > File "metaerror.py", line 18, in <module> > > > class C3(C1, C2): > > > TypeError: Error when calling the metaclass bases > > > Cannot create a consistent method resolution > > > order (MRO) for bases C2, C1 > > > > Since M3 is a subclass of M1 and M2 (which are the metaclasses for the > > > bases of C3, I don't understand the error. Then again, the error seems > > > to reference the MRO. > > > > I hope this is one of those posts that I can look back in a few months > > > from now and think "Man, was that a dumb thing to ask!" Until then, I > > > would appreciate your help in trying to figure out what's going on. > > >http://www.python.org/download/releases/2.3/mro/ > > > Carl Banks > > Thank you, I'll read on that paper too in order to figure out what is > going on. I guess the resulting MROs do not satisfy monotonicity, I > just have to find out how to derive the MRO. I had the notion that it > was constructed by listing the current class, followed by the MROs of > each base in order, and then retaining the rightmost instance of each > class in the MRO list, but I think that might be an > oversimplification, since in this case that would be: > (C1, object) > (C2, C1, object) > (C3, C2, C1, object) > And I don't see any issues. But I'll read the paper to figure out what > the problem is, thanks.
Thank you for pointing that paper. I read the paper and figured out what was wrong (local precedence is not maintained.) -- http://mail.python.org/mailman/listinfo/python-list
