Hi Simon, > On 2012-05-08, Florent Hivert <florent.hiv...@lri.fr> wrote: > > But it is never called. I'd like to have confirmation that adding to all > > vectors classes (following sage/structure/element.pyx line 881 (5.0.rc0)) > > > > def __richcmp__(left, right, int op): > > return (<Element>left)._richcmp(right, op) > > > > is the correct solution. > > Yes, the following advices given in some comment in > sage/structure/element.pyx are still valid (and, I agree, difficult > to keep in mind): > > #################################################################### > # For a derived Cython class, you **must** put the following in > # your subclasses, in order for it to take advantage of the > # above generic comparison code. You must also define > # either _cmp_c_impl (if your subclass is totally ordered), > # _richcmp_c_impl (if your subclass is partially ordered), or both > # (if your class has both a total order and a partial order; > # then the total order will be available with cmp(), and the partial > # order will be available with the relation operators; in this case > # you must also define __cmp__ in your subclass). > # This is simply how Python works. > # > # For a *Python* class just define __cmp__ as always. > # But note that when this gets called you can assume that > # both inputs have identical parents. > # > # If your __cmp__ methods are not getting called, verify that the > # canonical_coercion(x,y) is not throwing errors. > # > #################################################################### > > IIRC, the problem is that (by design of Cython) it is not possible to > inherit __(rich)cmp__ if there is also a __hash__ method. Anyway, > copying the code for __(rich)cmp__ from sage/structure/element.pyx is > necessary, inheritance wouldn't work, as I've learnt the hard way...
And it's not the end of the story: you also need to overload __hash__ if you do that. Cython assumes that if you change equality, you have to change __hash__ as well. __hash__ isn't inherited. Florent -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
