added hash

[eyalk11]

Added hash to Board class

[niklasf]

hash(self) == hash(board) does not imply self equals board (there can be hash collisions).

[eyalk11]

I am not sure I understand the claim. Are you claiming the hash is weak? Because hash collisions are negligible.

[niklasf]

Maybe for your use case.

But this is a general purpose library. So we shouldn't assume that we will only ever see 2^32 positions (at which point collisions are likely even for strong 64 bit hashes), or even that inputs aren't specifically chosen by an adversary.

[niklasf]

From https://docs.python.org/3/reference/datamodel.html#object.__hash__:

If a class defines mutable objects and implements an __eq__() method, it should not implement __hash__(), since the implementation of hashable collections requires that a key’s hash value is immutable (if the object’s hash value changes, it will be in the wrong hash bucket).