complete α-β evaluation of simple abstract games

README.md

written in notepad.exe and completely untested - Python has never seen this code :-)

alphabeta.py

# -*- coding: utf-8 -*-

class Game(object):
  
    @property
    def initial_position(self):
        # not actually used
        raise NotImplementedError
  
    def terminal_value(self, position):
      raise NotImplementedError

    def alphabeta(self, position, max_player, α=-math.inf, β=+math.inf):

        if self.terminal_value(position) is not None:
            return self.terminal(position)

        if max_player:
            value = -math.inf

        pick, value_seen, criterion = (max, -math.inf, operator.ge) \
                                      if max_player else \
                                      (min, +math.inf, operator.le)

        for successor in self.generate_successors(position):

            successor_value = self.alphabeta(successor, not max_player, α, β)
            value_seen = pick(value_seen, successor_value)
            α = pick(α, value)
            if α >=β:
                break
        return value