On Fri, 01 Aug 2014 14:17:41 +1000, Ben Finney wrote: > Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> writes: > >> On Thu, 31 Jul 2014 20:12:12 -0700, Dan Stromberg wrote: >> >> > I removed some quotes, and noticed that 1 and 1.0 hash the same. >> > That's a bit unexpected, but I suppose it's not completely >> > unreasonable. > > I would expect it, for the reasons Steven explains. Why is it > unexpected? > >> You should expect that two equal objects should hash to the same value >> in different versions of Python, or even from one run of Python to the >> next. > > I suspect there's a “not” missing there.
Thanks for spotting that. Correct, I meant that you should *not* expect hashing to return any specific value. [...] > If you expect the hash valuesto be the same, you're making a mistake; if > you expect the hash values to be different, you're making a mistake. Yes. Although Python promises (at least for classes in the standard library) that x == y should imply that hash(x) == hash(y), it says nothing about the other way: x == y implies that hash(x) == hash(y) but hash(x) == hash(y) does NOT imply that x == y. py> hash(2**128) == hash(1) True > The correct attitude, with regard to implementation details, is to > expect uncertainty and not assume anything :-) Yes, this! -- Steven -- https://mail.python.org/mailman/listinfo/python-list
