On Thu, Mar 12, 2009 at 12:47 PM, Robert Bradshaw <rober...@math.washington.edu> wrote: > > On Mar 12, 2009, at 11:23 AM, Carl Witty wrote: >> My suggestion in that thread of using "cmp" for sysorder is possible, >> but I doubt if it's a good idea... it makes it easy to make >> implementation mistakes, because by default cmp() and < use the same >> code. > > This could be changed, and probably would be a good thing (though a > lot of work--I don't know how much depends on the current semantics). > The cmp code isn't the prettiest right now. But I think this is a > distinct topic than whether or not to use coercions in comparison.
Note that "cmp" is gone in Python 3.1+, and it's illegal to compare values of incompatible types with "<" (although == still works). This is interesting for two reasons: if we think we're going to switch to Python 3 eventually, then it might be a bad idea to start introducing more dependencies on cmp; and as a style issue, we might want to look really hard at whether sysorder should support comparing values of incompatible types. Here's some text quoted from "What's new in Python 3.0" (http://docs.python.org/dev/3.0/whatsnew/3.0.html): Ordering Comparisons Python 3.0 has simplified the rules for ordering comparisons: * The ordering comparison operators (<, <=, >=, >) raise a TypeError exception when the operands don’t have a meaningful natural ordering. Thus, expressions like 1 < '', 0 > None or len <= len are no longer valid, and e.g. None < None raises TypeError instead of returning False. A corollary is that sorting a heterogeneous list no longer makes sense – all the elements must be comparable to each other. Note that this does not apply to the == and != operators: objects of different incomparable types always compare unequal to each other. * builtin.sorted() and list.sort() no longer accept the cmp argument providing a comparison function. Use the key argument instead. N.B. the key and reverse arguments are now “keyword-only”. * The cmp() function should be treated as gone, and the __cmp__() special method is no longer supported. Use __lt__() for sorting, __eq__() with __hash__(), and other rich comparisons as needed. (If you really need the cmp() functionality, you could use the expression (a > b) - (a < b) as the equivalent for cmp(a, b).) Carl --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
