>> And if there were something that would decide on context which of several >> implementations to use, you'd have less to worry. As things are, there >> isn't such thing (I don't even have the slightest idea what could work), >> you are as well off with defining two functions. > > But this "context decider" you're talking about sounds exactly like > what I'm talking about. If I had some class with __hash1__ and > __hash2__ (and associated equality operators), you're saying it would > be nice to be able to select which to use based on the context (e.g. > what type of set I'm using.) It might look like this: > > s = set(hash_func = lambda x: x.__hash2__, eq_func = lambda x, y: > x.__eq2__(y)) > > And if *that* works for you, do you still have a problem with: > > s = set(hash_func = lambda x: hash(x.name), eq_func = lambda x,y: > x.name == y.name) > > ? > > If you don't like those, what would work for you? As far as I can > tell, your "context decider" and my "alternative hash functions" are > the same thing, and we just need to agree on a syntax.
The context-decider isn't the same thing because it isn't designed yet :) And most probably won't ever be. It's just the abstract idea that hashing/equality change for one object depending on the circumstances they are used in, and that one wishes that the decision what to use is as simple & transparent as possible. Your approach is certainly viable, but I guess the current set-implementation is optimized on working with __hash__ and __eq__ on objects because for these exist slots in the python object structure in C. So while you can implement your idea, you will end up passing wrappers as Chris & me proposed into the current set implementation. However, it might be worth thinking of proposing this change to the set-type in general. But then for orthogonality, dicts should have it as well I guess. Which opens a whole new can of worms. I'm undecided on this. I think the cure is straight forward & simple to implement, and once you have the level to understand & need different hashing/equality, you should be comfortable writing this simple wrapper yourself. So for me personally, it's not a needed addition to the language. YMMV, and thus - go for it if you like. Diez -- http://mail.python.org/mailman/listinfo/python-list
