We need to get away from the __cmp__ to make the transition easier. Plus I would think most parents are not totally ordered.
Best, Travis On Sunday, October 26, 2014 3:08:15 AM UTC-7, Volker Braun wrote: > > Right now: only implement __cmp__ following what is written in > sage/structure/element.pyx, and not __eq__ and friends. You can play some > tricks with the __richcmp__ hook but its probably best to stick to a single > kind of comparison if you want your stuff to transition easily to python3. > > > On Sunday, October 26, 2014 9:57:49 AM UTC, Eric Gourgoulhon wrote: >> >> Hi, >> >> When implementing some algebra element class, I faced the following >> issue: the class inherits from >> sage.structure.element.CommutativeAlgebraElement and I've implemented the >> __eq__() and __ne__() methods, but not __cmp__() because my algebra is not >> an ordered set. Everything works well (the test suite for commutative >> algebras is passed by the parent), but if I construct matrices from algebra >> elements f1,...,f4, via >> a = matrix([[f1,f2], [f3,f4]]) >> and compare them by a == b, the following error appears: >> >> NotImplementedError: BUG: sort algorithm for elements of 'algebra of >> scalar fields on the 2-dimensional manifold 'M'' not implemented >> >> This is triggered by the lack of method __cmp__() in the algebra element >> class. Adding such method via >> >> def __cmp__(self, other): >> if self.__eq__(other): >> return 0 >> else: >> return -1 >> >> fixes the problem. >> >> Hence the question: shall __cmp__() be always implemented in element >> classes, even if the parent is not an ordered set ? If yes, what shall it >> return when the two elements differ ? -1 as above ? Shall __eq__() be >> implemented as well ? >> I've noticed that in line 919 of file src/sage/structure/element.pyx, it >> is written; >> >> # For a *Python* class just define __cmp__ as always. >> >> I've also noticed that in the example provided in the tutorial How to >> implement new algebraic structures in Sage >> <http://sagemath.org/doc/thematic_tutorials/coercion_and_categories.html>, >> only __cmp__() is implemented, not __eq__(). >> On the other side, __cmp__() has been withdrawn in Python 3 and only the >> rich comparison methods, like __eq__(), remain. >> >> Thanks for your advice on this. >> >> Eric. >> >> -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
