Examples of Python syntax

ttt.py

"""An immutable Tic Tac Toe board and minimax ai"""
import itertools

class Board(object):
    """Immutable Tic Tac Toe board

    >>> Board().rows
    ((' ', ' ', ' '), (' ', ' ', ' '), (' ', ' ', ' '))
    >>> print Board()
     | | 
    -----
     | | 
    -----
     | | 
    >>> Board().columns
    ((' ', ' ', ' '), (' ', ' ', ' '), (' ', ' ', ' '))
    >>> Board().turn
    0
    >>> Board().whose_turn
    'x'
    >>> b = Board().move(2); print b
     | |x
    -----
     | | 
    -----
     | | 
    >>> b.possible()
    [< Board |o.x......| >, < Board |.ox......| >, < Board |..xo.....| >, < Board |..x.o....| >, < Board |..x..o...| >, < Board |..x...o..| >, < Board |..x....o.| >, < Board |..x.....o| >]
    """
    def __init__(self, width=3, height=3):
        self._rows = [[' ' for _ in range(width)] for _ in range(height)]

    rows = property(lambda self: tuple(tuple(row) for row in self._rows))
    columns = property(lambda self: tuple(zip(*self._rows)))
    spots = property(lambda self: tuple(c for row in self._rows for c in row))
    def __str__(self):
        return ('\n'+'-'*(len(self.columns)*2-1) + '\n').join(['|'.join(row) for row in self._rows])
    def __repr__(self): return '< Board |'+''.join(self.spots).replace(' ','.')+'| >'
    def __eq__(self, other): return self.spots == other.spots
    @property
    def turn(self):
        return 9 - self.spots.count(' ')
    @property
    def whose_turn(self):
        return 'xo'[self.turn % 2]
    def winner(self):
        for c in 'xo':
            for comb in [(0,3,6), (1,4,7), (2,5,8), (0,1,2), (3,4,5), (6,7,8), (0,4,8), (2,4,6)]:
                if all(self.spots[p] == c for p in comb):
                    return c
        return None
    def move(self, pos):
        assert self.spots[pos] == ' '
        new = Board(len(self.rows), len(self.columns))
        new._rows = list(list(row) for row in self.rows)
        new._rows[pos / 3][pos % 3] = self.whose_turn
        return new
    def possible(self):
        return [self.move(p) for p in range(len(self.spots)) if self.spots[p] == ' ']

def opp(c):
    """
    >>> opp('x'), opp('o')
    ('o', 'x')
    """
    return 'x' if c == 'o' else 'o'

def value(board, who='x'):
    """Returns the value of a board
    >>> b = Board(); b._rows = [['x', 'x', 'x'], ['x', 'x', 'x'], ['x', 'x', 'x']]
    >>> value(b)
    1
    >>> b = Board(); b._rows = [['o', 'o', 'o'], ['o', 'o', 'o'], ['o', 'o', 'o']]
    >>> value(b)
    -1
    >>> b = Board(); b._rows = [['x', 'o', ' '], ['x', 'o', ' '], [' ', ' ', ' ']]
    >>> value(b)
    1
    >>> b._rows[0][2] = 'x'
    >>> value(b)
    -1
    """
    w = board.winner()
    if w == who: return 1
    if w == opp(who): return -1
    if board.turn == 9: return 0
    if who == board.whose_turn: return max([value(b, who) for b in board.possible()])
    else: return min([value(b, who) for b in board.possible()])

def ai(board):
    """Returns best next board

    >>> b = Board(); b._rows = [['x', 'o', ' '], ['x', 'o', ' '], [' ', ' ', ' ']]
    >>> ai(b)
    < Board |xo.xo.x..| >
    >>> b = Board(); b._rows = [['x', ' ', ' '], [' ', 'x', 'o'], [' ', ' ', ' ']]
    >>> ai(b)
    < Board |x...xo..o| >
    """
    return sorted([(value(b, who=board.whose_turn), b) for b in board.possible()])[-1][1]

def human(board):
    """Returns the next board as selected by raw_input"""
    while True:
        x = int(raw_input('x:'))
        y = int(raw_input('y:'))
        if not (0 <= x <= 2 and 0 <= y <= 2): continue
        s = x + y*3
        if board.spots[s] != ' ': continue
        return board.move(x+y*3)

def play():
    b = Board()
    for player in itertools.cycle([human, ai]):
        print player.__name__, 'move...'
        print b
        b = player(b)
        if b.winner() or b.turn == 9:
            break
    print '%s won!' % (b.winner() or 'no one')

if __name__ == '__main__':
    import doctest
    doctest.testmod(verbose=True)
    play()