On Jul 5, 2008, at 12:42 PM, John H Palmieri wrote: >> >> >>>> Ah, it looks like your __eq__ method is assuming that self and >>>> other >>>> are elements of the steenrod algebra. There are two solutions to >>>> this: >> >>>> 1) Use __cmp__ which (in Sage) will ensure that self and other have >>>> the same parent before it's called >>>> 2) Fix your __eq__ (and any other comparison methods you might >>>> have) >>>> to make sure self-other makes sense (or, as a quick fix, catch the >>>> type error here). >> >>> I still don't understand two things: why the gen method is being >>> used, >>> and why if I multiply an element of SteenrodAlgebra(7) by 3, somehow >>> elements of SteenrodAlgebra(5) are getting involved. >> >> I'm not seeing where the gen method is being used--it's probably to >> get a "generic" element to see if multiplication is a viable option. >> As for elements of SteenrodAlgebra(7) and SteenrodAlgebra(5) getting >> compared, that's because it's looking up something in a (global-ish) >> lookup table that happens to have SteenrodAlgebra(5) in it as well. >> Obviously equality here should return False. >> > > So, for example, for the definition of the __eq__ method for > SteenrodAlgebraElement, replacing > > difference = self - other > return len(difference._raw['milnor']) == 0 > > with > > if self.parent() == other.parent(): > difference = self - other > return len(difference._raw['milnor']) == 0 > else: > return False > > would be good enough? (That is, assuming I've defined a reasonable > __eq__ method for the parents, the SteenrodAlgebra class.)
Yes, though that will mean something like A5.P(2) - A5.P(2) == 0 will return False. This is why you are better off using _cmp_ instead of __eq__, __ne__, __le__, __gt__, ... (also, the latter are deprecated in Python). The _cmp_ method will always be called with two things of the same parent, invoking coercion if necessary. - Robert --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
