[Python-ideas] incremental hashing in __hash__

[Chris Angelico]

On Sat, Dec 31, 2016 at 2:24 PM,  <jab at math.brown.edu> wrote:
> See the "Simply XORing such results together would not be order-sensitive,
> and so wouldn't work" from my original post. (Like XOR, multiplication is
> also commutative.)
>
> e.g. Since FrozenOrderedCollection([1, 2]) != FrozenOrderedCollection([2,
> 1]), we should try to avoid making their hashes equal, or else we increase
> collisions unnecessarily.

How likely is it that you'll have this form of collision, rather than
some other? Remember, collisions *will* happen, so don't try to
eliminate them all; just try to minimize the chances of *too many*
collisions. So if you're going to be frequently dealing with (1,2,3)
and (1,3,2) and (2,1,3) and (3,1,2), then sure, you need to care about
order; but otherwise, one possible cause of a collision is no worse
than any other. Keep your algorithm simple, and don't sweat the
details that you aren't sure matter.

ChrisA