players.py

import random

class Player(object):
    def __init__(self, symbol, number):
        self._symbol = symbol
        self._number = number
        self._string = 'Player %d (%s)' % (number, symbol)

    def __str__(self):
        return self._string

    @property
    def symbol(self):
        return self._symbol

    @property
    def number(self):
        return self._number

    def chooseMove(self, board):
        raise NotImplementedError

class Human(Player):
    def chooseMove(self, board):
        while True:
            move = raw_input('Enter your move: ')
            try:
                square = board.getByHuman(move)
            except ValueError as e:
                print e
                continue

            if square.empty():
                break
            print 'invalid move: %s is already taken' % move

        return square

class Random(Player):
    def chooseMove(self, board):
        empties = list(board.emptySquares())
        square = random.choice(empties)
        return square

def distanceFromCentre(square, centre):
    return sum(abs(centre - index) for index in square.indexes)

class Centre(Player):
    def chooseMove(self, board):
        centre = board.size / 2
        empties = board.emptySquares()
        closest = []
        minDistance = None
        for square in empties:
            distance = distanceFromCentre(square, centre)
            if minDistance is None or distance < minDistance:
                minDistance = distance
                closest = [square]
            elif minDistance == distance:
                closest.append(square)

        square = random.choice(closest)
        return square