Following the instructions given in the book listed above, I attempted to improve a Tic-Tac-Toe game I constructed earlier to make it unwinnable. Now, I did eventually succeed in this task, but the reason I'm here is that I failed to understand why my initial solution was ineffective.
Here is the original, unedited code:
#Tic-Tac-Toe
#Plays a game of Tic-Tac-Toe against a human opponent
#Global constants
X = "X"
O = "O"
EMPTY = " "
TIE = "TIE"
NUM_SQUARES = 9
def display_instruct():
"""Diplsay game instructions."""
print(
"""
Welcome to the greatest inetellectual challenge of all time: Tic-Tac-Toe.
This will be a showdown between your rudimentary human brain and my superior
silicon processor.
You will make your move 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
"""
)
def ask_yes_no(question):
"""Ask a yes or no question."""
response = None
while response not in ("y", "n"):
response = input(question).lower()
return response
def ask_number(question, low, high):
"""Ask for a number within a range."""
response = None
while response not in range(low, high):
response = int(input(question))
return response
def pieces():
"""Determine if playor or computer goes first"""
go_first = ask_yes_no("Do you require the first move? (y/n): ")
if go_first == "y":
print("\nThen take the first move. You will need it.")
human = X
computer = O
else:
print("\nYour bravery will be your undoing... I will go first.")
computer = X
human = O
return computer, human
def new_board():
"""Create new game baord."""
board = []
for square in range(NUM_SQUARES):
board.append(EMPTY)
return board
def display_board(board):
"""Display game board on 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")
def legal_moves(board):
"""Creates a list of legal moves."""
moves = []
for square in range(NUM_SQUARES):
if board[square] == EMPTY:
moves.append(square)
return moves
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
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:
print("\nThat square is already occipied, foolish hooman. Choose another.\n")
print("Fine...")
return move
def computer_move(board, computer, human):
"Make computer move."""
#Make a copy to work with since function will be changing 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 square number", end=" ")
#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 option square
for move in BEST_MOVES:
if move in legal_moves(board):
print(move)
return move
def next_turn(turn):
"""Switch turns."""
if turn == X:
return O
else:
return X
def congrat_winner(the_winner, computer, human):
"""Congratulate the winner."""
if the_winner != TIE:
print(the_winner, "won!\n")
else:
print("It's a tie\n")
if the_winner == computer:
print("As I predicted hooman, I am triumphant! \n" \
"proof that silicon is superior to flesh in all regards.")
elif the_winner == human:
print("No, no! It cannot be! Somehow you tricked me, ape. \n" \
"But never again, I, the computer, so swear it!")
elif the_winner == TIE:
print("You were most fortunate, hooman, and somehow managed to tie me. \n" \
"Celebrate today... for this is the best you will ever achieve.")
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()
input("\n\nPress the enter key to quit.")
And here is what I initially tried to do:
#Tic-Tac-Toe
#Plays a game of Tic-Tac-Toe against a human opponent
#Global constants
X = "X"
O = "O"
EMPTY = " "
TIE = "TIE"
NUM_SQUARES = 9
human_moves_so_far = []
def display_instruct():
"""Diplsay game instructions."""
print(
"""
Welcome to the greatest inetellectual challenge of all time: Tic-Tac-Toe.
This will be a showdown between your rudimentary human brain and my superior
silicon processor.
You will make your move 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
"""
)
def ask_yes_no(question):
"""Ask a yes or no question."""
response = None
while response not in ("y", "n"):
response = input(question).lower()
return response
def ask_number(question, low, high):
"""Ask for a number within a range."""
response = None
while response not in range(low, high):
response = int(input(question))
return response
def pieces():
"""Determine if playor or computer goes first"""
go_first = ask_yes_no("Do you require the first move? (y/n): ")
if go_first == "y":
print("\nThen take the first move. You will need it.")
human = X
computer = O
else:
print("\nYour bravery will be your undoing... I will go first.")
computer = X
human = O
return computer, human
def new_board():
"""Create new game baord."""
board = []
for square in range(NUM_SQUARES):
board.append(EMPTY)
return board
def display_board(board):
"""Display game board on 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")
def legal_moves(board):
"""Creates a list of legal moves."""
moves = []
for square in range(NUM_SQUARES):
if board[square] == EMPTY:
moves.append(square)
return moves
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
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:
print("\nThat square is already occipied, foolish hooman. Choose another.\n")
print("Fine...")
human_moves_so_far.append(move)
return move
def computer_move(board, computer, human):
"Make computer move."""
#Make a copy to work with since function will be changing 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 square number", end=" ")
#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
if human_moves_so_far == [0, 8] or [8, 0] or [6, 2] or [2, 6]:
move = 7
return move
#Since no one can win on next move, pick best option square
for move in BEST_MOVES:
if move in legal_moves(board):
print(move)
return move
def next_turn(turn):
"""Switch turns."""
if turn == X:
return O
else:
return X
def congrat_winner(the_winner, computer, human):
"""Congratulate the winner."""
if the_winner != TIE:
print(the_winner, "won!\n")
else:
print("It's a tie\n")
if the_winner == computer:
print("As I predicted hooman, I am triumphant! \n" \
"proof that silicon is superior to flesh in all regards.")
elif the_winner == human:
print("No, no! It cannot be! Somehow you tricked me, ape. \n" \
"But never again, I, the computer, so swear it!")
elif the_winner == TIE:
print("You were most fortunate, hooman, and somehow managed to tie me. \n" \
"Celebrate today... for this is the best you will ever achieve.")
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()
input("\n\nPress the enter key to quit.")
Specifically, I created a list called "human_moves_so_far" which (I thought) I could use to track the moves of the human player, and if they entered one of the four specific sequences of moves that the computer could not defeat, the computer would temporarily abandon its normal order of move priority and stop them.
Now, upon further inspection, I realize that this solution may not have resulted in an unwinnable game, but I am not here to ascertain how to complete the challenge, but rather to understand why the computer began behaving the way that it did.
See, after I attempted the solution, the computer would ALWAYS take square 7 on its first move, regardless of what the player did, and I don't know why it started doing that. It's as if it ignored the 'if' statement entirely and simply executed the code.
Now that I look again I wonder if maybe I missed the 'or' statement; can anyone tell me if that's the problem, or if not, what is? I think it's important for my learning process to understand what I did wrong, even if I did eventually find another way. Thank you.
P.S: This is the final version of the game, which is, as far as I can attest, impossible. Just in case anyone is curious.
#Tic-Tac-Toe
#Plays a game of Tic-Tac-Toe against a human opponent
#Global constants
X = "X"
O = "O"
EMPTY = " "
TIE = "TIE"
NUM_SQUARES = 9
fatal_flaw = []
def display_instruct():
"""Diplsay game instructions."""
print(
"""
Welcome to the greatest inetellectual challenge of all time: Tic-Tac-Toe.
This will be a showdown between your rudimentary human brain and my superior
silicon processor.
You will make your move 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
"""
)
def ask_yes_no(question):
"""Ask a yes or no question."""
response = None
while response not in ("y", "n"):
response = input(question).lower()
return response
def ask_number(question, low, high):
"""Ask for a number within a range."""
response = None
while response not in range(low, high):
response = int(input(question))
return response
def pieces():
"""Determine if playor or computer goes first"""
go_first = ask_yes_no("Do you require the first move? (y/n): ")
if go_first == "y":
print("\nThen take the first move. You will need it.")
human = X
computer = O
else:
print("\nYour bravery will be your undoing... I will go first.")
computer = X
human = O
return computer, human
def new_board():
"""Create new game baord."""
board = []
for square in range(NUM_SQUARES):
board.append(EMPTY)
return board
def display_board(board):
"""Display game board on 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")
def legal_moves(board):
"""Creates a list of legal moves."""
moves = []
for square in range(NUM_SQUARES):
if board[square] == EMPTY:
moves.append(square)
return moves
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 the board:
return TIE
return None
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:
print("\nThat square is already occipied, foolish hooman. Choose another.\n")
print("Fine...")
if move == 2:
fatal_flaw.append("GAME")
if move == 6:
fatal_flaw.append("OVER")
if move == 0:
fatal_flaw.append("CHECK")
if move == 8:
fatal_flaw.append("MATE")
return move
def computer_move(board, computer, human):
"Make computer move."""
#Make a copy to work with since function will be changing list
board = board[:]
#The best positions to have, in order
if "GAME" in fatal_flaw and "OVER" in fatal_flaw or "CHECK" in fatal_flaw and "MATE" in fatal_flaw:
BEST_MOVES = (7, 4, 0, 2, 6, 8, 1, 3, 5)
else:
BEST_MOVES = (4, 0, 2, 6, 8, 1, 3, 5, 7)
print("I shall take square number", end=" ")
#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 option square
for move in BEST_MOVES:
if move in legal_moves(board):
print(move)
return move
def next_turn(turn):
"""Switch turns."""
if turn == X:
return O
else:
return X
def congrat_winner(the_winner, computer, human):
"""Congratulate the winner."""
if the_winner != TIE:
print(the_winner, "won!\n")
else:
print("It's a tie\n")
if the_winner == computer:
print("As I predicted hooman, I am triumphant! \n" \
"proof that silicon is superior to flesh in all regards.")
elif the_winner == human:
print("No, no! It cannot be! Somehow you tricked me, ape. \n" \
"But never again, I, the computer, so swear it!")
elif the_winner == TIE:
print("You were most fortunate, hooman, and somehow managed to tie me. \n" \
"Celebrate today... for this is the best you will ever achieve.")
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()
input("\n\nPress the enter key to quit.")
The reason your code always executes the contents of the if statement is due to the way Python handles your or statements.
if human_moves_so_far == [0, 8] or [8, 0] or [6, 2] or [2, 6]:
Repeating or for each number combination does not associate it with your first statement, if human_moves_so_far ==.
Even if human_moves_so_far == [0, 8] resolves to False, or [8, 0] will always resolve to True, so the if statement is activated.
In other words, this line should look like:
if (human_moves_so_far == [0, 8]) or (human_moves_so_far == [8, 0]) or (human_moves_so_far == [6, 2]) or (human_moves_so_far == [2, 6]):
Alternatively, you could write the code using an in statement, making the if statement continue if the variable is within a given list, like so:
if human_moves_so_far in [[0, 8],[8, 0],[6, 2],[2, 6]]: