Mark Dickinson wrote:
On Thu, Mar 13, 2008 at 6:18 PM, Imri Goldberg <lorgandon@gmail.com <mailto:lorgandon@gmail.com>> wrote:
This makes changing == behavior to an epsilon comparison more involved. I still think it is feasible, but will require much more consideration.
Okay, now I am going to be negative. :-)
I really think that there's essentially zero chance of == and != ever changing to 'fuzzy' comparisons in Python. I don't want to discourage you from working out possible details as an academic exercise, or perhaps with some other (Python-like?) language in mind, but I just don't see it ever happening in Python. Maybe I'm wrong, in which case I hope other python people will tell me so, but I think pursuing this is, in the end, going to be a waste of time.
Alright, I agree it's a good idea to drop the proposal to changing floating point == into an epsilon compare. What about issuing a warning though? Consider the following course of action. It is the one with the least changes: == for regular floating point numbers now issues a warning, but still works. This warning might be turned off. All other operators are left unchanged. Do you think this should be dropped as well? Just for my own code, I think I'd like this behavior. I still consider floating point == a potential bug, and this helps me catch it, in the absence of the 'ideal static checker'.
Containers would be affected in peculiar ways. I think people would be really surprised to find that 1.0+2e-16 *was* an element of the set {1.0}, or that 1.0 and 1.0+2e-16 weren't allowed to be different keys in a dict. And how on earth do you check for set or dict membership under the hood?
I think that right now containers behave in peculiar ways when used with FP numbers. Take set for example - you might as well just use list instead of it. When you consider dict, then doing d[x] might not return the result you actually want.
I don't know of any other language that has successfully done this, even though I've seen the idea floated many times for different languages. That doesn't mean much, since I only know a small handful of the many hundreds (thousands?) of languages out there. If you know a counterexample, I'd be interested to hear it.
Mark Don't know of a good counterexample. I agree that before changing the behavior of == to fuzzy comparison, you'll want experience with that kind of change.
Cheers, Imri ------------------------- Imri Goldberg www.algorithm.co.il/blogs www.imri.co.il ------------------------- Insert Signature Here -------------------------