A program that plays Tic-tac-toe with you and tries to lose. Uses Minimax rule to evaluate possible moves.

worstMove.py

"""
Write a program that plays Tic-tac-toe with you and tries its best to lose
"""

def printBoard(b):
	for i in range(3):
		print(b[3*i], b[3*i+1], b[3*i+2])

def getNext(b):
	move = int(input("Your move, sir (must be a number from 1 to 9): ")) - 1
	if 0 <= move < 9 and b[move] == '-':
		b[move] = 'x'
	else:
		getNext(b)

# Use Minimax to find the worst move
def worstMove(b, player): 
	if len(set(b)) == 1: # no moves yet, 1 seems bad enough
		return 0, 1

	if win(b): # the previous player's move won the game
		return -1, -1

	if '-' not in b: # no more empty cells, game finished
		return 0, -1

	next_player = 'x' if player == 'o' else 'o'
	scores = []

	for i in range(len(b)):
		if b[i] == '-':
			b[i] = player
			scores.append((-worstMove(b, next_player)[0], i))
			b[i] = '-'

	return min(scores)

def win(b):
	return (b[0]==b[1]==b[2]!='-' or b[3]==b[4]==b[5]!='-' or
			b[6]==b[7]==b[8]!='-' or b[0]==b[3]==b[6]!='-' or
			b[1]==b[4]==b[7]!='-' or b[2]==b[5]==b[8]!='-' or
			b[0]==b[4]==b[8]!='-' or b[2]==b[4]==b[6]!='-')

def makeMove(b):
	move = worstMove(b, 'o')
	b[move[1]] = 'o'

if __name__ == '__main__':
	ticTacToe = ['-']*9

	tricked = False

	while not win(ticTacToe):
		printBoard(ticTacToe)
		getNext(ticTacToe)
		if win(ticTacToe):
			print("You won! I tricked you.")
			tricked = True
		else:
			makeMove(ticTacToe)

	if not tricked:
		print("You're too smart, I couldn't trick you to win.")