Robert Bradshaw <[EMAIL PROTECTED]> writes: > On Oct 14, 2008, at 1:33 PM, Martin Rubey wrote: > > > > > I believe I understood now: > > > > sage: ?parent > > Type: function > > <snip> > > Return x.parent() if defined, or type(x) if not. > > > > I wonder why this is a function, and not a method of Parent? > > Typically one uses the parent() function when one has an element > (such as an integer) and wants it's Parent. This is why it's not an > element of the Parent.
Hm, I do not understand that. Why wouldn't one want to use 5.parent(), for example? (The method notation together with tab completion is really nice...) Well, I suppose that some people prefer usual functional notation. > The docstring should have some better examples, e.g. > > sage: parent(5) > Integer Ring > sage: parent(1/2) > Rational Field > sage: parent(1.5) > Real Field with 53 bits of precision Well, actually, I find the current docstring OK, it answered my question, at least partially. OK, maybe some more examples wouldn't hurt. But what I really do not understand is why Parent doesn't implement a parent method... > > (Am I right that all Sage parents inherit from Parent? Would be great to > > know this) > > Yes, that is correct. OK, great. > > Set_object inherits from Set_generic, and does not define a parent method, > > for whatever reason, maybe because the elements of the set need not have a > > common type. > > > > I just saw on > > http://trac.sagemath.org/sage_trac/attachment/ticket/2314/ > > coerce_2_sets.patch > > > > a patch to primes.py, which, in particular, makes Primes inherit from a new > > class Subset instead of Set_generic. I guess this adresses the issue. > > > > It would be wonderful to hear either of "yes, correct", or "no, you are > > mistaken". > I'm not sure exactly what your question is, The question was, why does parent(Primes()) give an answer, while Primes().parent() yields an error. > but sets don't really have a parent, well, they do: sage: parent(Set([1,2,3])) <class 'sage.sets.set.Set_object_enumerated'> ;-) I think it's ok to have things without parent, but I do not understand yet, why x.f() and f(x) are designed differently in some cases. One case I stepped into was parent, the other was Mod. > as the set of all sets is not a category. Äh? You don't mean category in the mathematical sense here, do you? http://en.wikipedia.org/wiki/Category_of_sets Does Sage have it's own notion of category, just as FriCAS? (since "set of all sets" doesn't make sense, I guess you mean "class of all sets") Martin --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
