There is now a patch for this at: http://trac.sagemath.org/sage_trac/ticket/10470
On Dec 22 2010, 2:09 pm, "Nicolas M. Thiery" <nicolas.thi...@u- psud.fr> wrote: > Hi Rob! > > > > On Tue, Dec 14, 2010 at 03:09:55PM -0800, Rob Beezer wrote: > > Symptom: The following code would appear to run forever, since the > > rationals define an iterator that never quits. > > > QQ.list() > > > I discovered this when I presumed that > > > (QQ^2).list() > > > would raise an error. It doesn't. So I patched the free module code > > so the iterator producing module elements would raise an error for a > > module over an infinite base ring. That very nearly passed all tests, > > except it ran afoul of the category test suite. A doctest for sets > > (in the Set_object_union class) constructs a vector space. To get a > > generic element for testing the test suite would appear to build an > > iterator and then grab the first element produced, so my fix broke > > that. (This appears to be at > > categories.enumerated_sets._an_element_from_iterator) > > > It looks like structure.parent._list_from_iterator_cached is where > > the first examples get stuck, at least that looks like the right place > > when you read the code and that's part of the traceback when you use > > ctrl-C. > > > Options: > > > 1. _list_from_iterator_cached could ask if self is infinite and if > > so, fail. This would break the test suite too, I think. > > > 2. The test suite framework needs to get an element by some other > > process. For example, (QQ^2).an_element() did not break with my > > patch. > > > 3. Tough. You ought to check if a set is infinite before you try to > > list it (and students should just learn to do that). > > > 4. Something else. > > > I've attached one failure of the test suite from my patch to the > > module code, there were four very similar failures from the one test: > > _test_an_element, _test_elements, _test_elements_eq, > > _test_some_elements. The last error message is from my patch. > > > I'd started this as: http://trac.sagemath.org/sage_trac/ticket/10470 > > > I would prefer to have modules raise an error rather than just hang. > > If desired, I can try to fix more fundamental situations, like > > ZZ.list(). Comments and suggestions appreciated. > > The list method from InfiniteEnumeratedSets() does just that. So here > is a possible route: > > - There should be an InfiniteSets() category > - QQ should be in this category > - The list method from InfiniteEnumeratedSets() should be lifted to > InfiniteSets() > > Shorter alternative: QQ could be in InfiniteEnumeratedSets(). But for > which one of the possible enumerations? > > For the record, I am planning to work in the coming month(s?) on > improving the category framework to support "variants" (see [1]); this > should include InfiniteSets as a side product. > > Cheers, > Nicolas > > [1]http://trac.sagemath.org/sage_trac/wiki/CategoriesRoadMap > -- > Nicolas M. Thi ry "Isil" <nthi...@users.sf.net>http://Nicolas.Thiery.name/ -- 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
