# [Tutor] Todays Learning Python Question From a Newbie ;)

Jon Moore jonathan.r.moore at gmail.com
Thu Feb 2 11:31:05 CET 2006

```On 02/02/06, Alan Gauld <alan.gauld at freenet.co.uk> wrote:
>
> Bob,
>
> >> Write a new computer_move() function for the tic-tac-toe game to plug
> >> the hole in the computers stratergy. See if you can create an opponent
> >> that is unbeatable!
> >>
> >> My main problem is that I can not see how the computers stratergy can
> >> be improved as at best I can only manage a tie with the computer!
>
> Does the computer ever go first?

Yes if you let it!

No, if you look at the code below, it has a  predefined set of 'best moves'.

If yes to the above then the computer can be beaten since the entire
> course of a Tic-Tac-Toe game (or OXO as we call it in the UK!)
> depends upon the first move location.

Thanks to  André, there is a way to win every time if you take the first
move (see below), so there MUST be a whole in the computers stratergy! Based
on what we all know about the game, I would say that you can not make it so
that the computer can win every time, but it should be possable to make it
tie.

x: 0
o: 4
x: 7
o: 2
x: 6

If no to the above then, provided the gameplay is OK, I don't know
> what the author means either.
>
> Alan G.
>

The code is as follows:

# set global constants
X = "X"
O = "O"
EMPTY = " "
TIE = "TIE"
NUM_SQUARES = 9

# set game instructions
def display_instruct():
"""Display game instructions."""
print \
"""
Welcome to the greatest intellectual challenge of all time:
Tic-Tac-Toe.
This will be a showdown between your human brain and my silicon
processor.

You will make your move known by entering a number, 0 - 8.  The number
will correspond to the board position as illustrated:

0 | 1 | 2
---------
3 | 4 | 5
---------
6 | 7 | 8

Prepare yourself, human.  The ultimate battle is about to begin. \n
"""

# set question
"""Ask a yes or no question."""
response = None
while response not in ("y", "n"):
response =  raw_input(question).lower()
return response

"""Ask for a number within the range"""
response = None
while response not in range(low, high):
response =  int(raw_input(question))
return response

# set pieces
def pieces():
"""Determine if player or computer goes first."""
go_first =  ask_yes_no("Do you wish to go first? (y/n): ")
if go_first == "y":
print "\nThen take the first move. You will need it ;)"
human = X
computer = O
else:
computer = X
human = O
return computer, human

# create new board
def new_board():
"""Create a new game board."""
board = []
for square in range(NUM_SQUARES):
board.append(EMPTY)
return board

# display the board
def display_board(board):
"""Display the board on the screen"""
print "\n\t", board[0], "|", board[1], "|", board[2]
print "\t", "---------"
print "\t", board[3], "|", board[4], "|", board[5]
print "\t", "---------"
print "\t", board[6], "|", board[7], "|", board[8], "\n"

# set legal moves
def legal_moves(board):
"""Create list of legal moves."""
moves = []
for square in range(NUM_SQUARES):
if board[square] == EMPTY:
moves.append(square)
return moves

# set winner
def winner(board):
"""Determine the game winner"""
WAYS_TO_WIN = ((0, 1, 2),
(3, 4, 5),
(6, 7, 8),
(0, 3, 6),
(1, 4, 7),
(2, 5, 8),
(0, 4, 8),
(2, 4, 6))

for row in WAYS_TO_WIN:
if board[row[0]] == board[row[1]] == board[row[2]] != EMPTY:
winner = board[row[0]]
return winner

if EMPTY not in board:
return TIE
return None

# set human move
def human_move(board, human):
"""Get human move."""
legal = legal_moves(board)
move = None
while move not in legal:
move = ask_number("Where will you move? (0-8): ", 0, NUM_SQUARES)
if move not in legal:
another.\n"
print "Fine..."
return move

# set computer move
def computer_move(board, computer, human):
"""Make computer move."""
# Make a copy of the board to work with since the function will be
changing the list
board = board[:]
# The best positions to have, in order
BEST_MOVES = (4, 0, 2, 6, 8, 1, 3, 5, 7)

print "I shall take a square number",
# if computer can win, take that move
for move in legal_moves(board):
board[move] = computer
if winner(board) ==  computer:
print move
return move
# done checking this move, undo it
board[move] = EMPTY

#if human can win, block that move
for move in legal_moves(board):
board[move] = human
if winner(board) ==  human:
print move
return move
# done checking this move, undo it
board[move] = EMPTY

# since no one can win on next move, pick best open square
for move in BEST_MOVES:
if move in legal_moves(board):
print move
return move

# set next turn
def next_turn(turn):
"""Switch turns."""
if turn == X:
return O
else:
return X

# congratulate winner
def congrat_winner(the_winner, computer, human):
"""Congratulate the winner"""
if the_winner != TIE:
print the_winner, "won!\n"
else:
print "Its a tie!\n"

if the_winner == computer:
print "As I predicted human, I am triumphant once more. \n" \
"Proof that computers are superior to humans in all regards."

elif the_winner == human:
print "Nooooo! It cannot be! Somehow you tricked me human! \n" \
"But never again.......I will win next time!"

elif the_winner == TIE:
print "You were most lucky human, and somehow managed to tie me! \n"
\
"Celebrate today....for this will not happen again!"

# set main function
def main():
display_instruct()
computer, human = pieces()
turn = X
board = new_board()
display_board(board)

while not winner(board):
if turn == human:
move = human_move(board, human)
board[move] = human
else:
move = computer_move(board, computer, human)
board[move] = computer
display_board(board)
turn = next_turn(turn)

the_winner =  winner(board)
congrat_winner(the_winner, computer, human)

# start the program
main()

raw_input("\n\nPress the enter key to exit.")
--
Best Regards

Jon Moore
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.python.org/pipermail/tutor/attachments/20060202/e5bc7f59/attachment-0001.htm
```