Threefold repetition detection and fifty-move rule about python-chess

[niklasf]

Hi @jromang, PicoChess looks pretty awesome, from what I can tell without a DGT board. Maybe I should get one, finally.

I have always wanted to build Zobrist hashes incrementally to allow building a repitition table in an efficient way. I did that now.

The old attribute board.halfmove_clock remains.

The next version of python-chess v0.4.0 has can_claim_draw(), can_claim_fifty_moves() and can_claim_threefold_repitition().

Details: is_game_over() will still return False, because those draws need to be claimed. A threefold repitition can be claimed when it occurs but also when it could occur with the next legal move. It's too late to claim a draw if the game ended in a different way.

Aditionally I added is_seventyfive_moves() and is_fivefold_repitition(). Those drawing rules were only recently (July) introduced. They end the game (and affect is_game_over()) even without a claim. Other ways of ending a game take precedence.

Niklas

[jromang]

That was quick ! Thank you very much.