Steven D'Aprano <st...@remove-this-cybersource.com.au> writes: > On Sat, 09 Oct 2010 21:39:51 +0100, Arnaud Delobelle wrote: > >> 1. hash() is an idempotent function, i.e. hash(hash(x)) == hash(x) hold >> for any hashable x (this is a simple consequence of the fact that >> hash(x) == x for any int x (by 'int' I mean 2.X int)). > > It's a beautiful theory, but, alas, it is not the case. > >>>> hash(-1) == -1 > False
This is a counter-example for the (invalid) premise that hash(x) == x, but not for the invariant of hash(hash(x)) == hash(x). >>> hash(hash(-1)) == hash(-1) True >>> hash(hash(2**64)) == hash(2**64) True > Aside: what do you mean by '2.x int'? Do you mean an int in 2.x versions > before, or after, ints and longs were partially integrated? I would take it to mean the type 2.x calls 'int', i.e. fixed-width integer type. -- http://mail.python.org/mailman/listinfo/python-list