On Tue, Mar 16, 2010 at 9:07 AM, Mark Dickinson <dickinsm@gmail.com> wrote:
On Tue, Mar 16, 2010 at 4:41 PM, Guido van Rossum <guido@python.org> wrote:
I'd say if you're not going to forward-port this to Python 3, it shouldn't go into Python 2 -- in that case it would make more sense to me to back-port the exception-raising behavior.
That's also a possible solution, and the one that I'd personally be happiest with. The main problem is that this has the potential to break code: lists containing both floats and Decimals are sortable in 2.6, but would no longer be sortable in 2.7. If such breakage is deemed acceptable then I'd happily backport the exception; I really don't have a good feeling for how much real-world code could break, if any.
Definitely some. Stricter comparison rules are a frequent cause of problems when code is first ported to 3.x. While you'd think that code comparing a float and a Decimal is *already* broken, there's a surprising number of situations where that's not necessary the case, e.g. when an arbitrary but stable ordering is needed.
Also supporting comparisons but not other mixed operations is going to be confusing. If you are sticking to that behavior I think mixed comparisons should also be ruled out.
Confusing, yes, but at least not bug-prone. The current 2.x behaviour has provoked complaints from a number of different people in various different fora (I recently saw this come up on StackOverflow), and after initially being skeptical I'm now convinced that it would be a good idea to change it if at all possible.
Yeah, it should have raised an exception all along. But it's too late for that now. I wonder if it should just become a py3k warning? -- --Guido van Rossum (python.org/~guido)