I am a young programmer that is learning python and struggling to implement an AI (using minimax) to play TicTacToe. I started watching a tutorial online, but the tutorial was on JavaScript and thus couldn't solve my problem. I also had a look at this question ( Python minimax for tictactoe ), but it did not have any answers and the implementation was considerably different from mine.
EDIT: the code you will find below is an edit suggested by one of the answers (@water_ghosts).
EDIT #2: I deleted possiblePositions, as the AI should choose a free field and not a place from the possiblePositions (that wouldn't make it that smart while implementing minimax :) )
Now the code doesn't give out any errors at all and functions properly, but one small thing: the AI always chooses the next available field. For example in situations where i am i move away from winning, instead of blocking my win option, it chooses the next free spot.
If you're wondering what that elements dict is doing there: i just wanted to make sure the programm chose the best index...
Here is my code:
class TicTacToe:
def __init__(self):
self.board = [" ", " ", " ", " ", " ", " ", " ", " ", " "]
self.playerSymbol = ""
self.playerPosition = []
self.aiSymbol = ""
self.aiPosition = []
self.score = 0
self.winner = None
self.scoreBoard = {
self.playerSymbol: -1,
self.aiSymbol: 1,
"tie": 0
}
self.turn = 0
self.optimalMove = int()
def drawBoard(self):
print(self.board[0] + " | " + self.board[1] + " | " + self.board[2])
print("___" + "___" + "___")
print(self.board[3] + " | " + self.board[4] + " | " + self.board[5])
print("___" + "___" + "___")
print(self.board[6] + " | " + self.board[7] + " | " + self.board[8])
def choice(self):
answer = input("What do you want to play as? (type x or o) ")
if answer.upper() == "X":
self.playerSymbol = "X"
self.aiSymbol = "O"
else:
self.playerSymbol = "O"
self.aiSymbol = "X"
def won(self):
winningPositions = [{0, 1, 2}, {3, 4, 5}, {6, 7, 8}, {0, 4, 8}, {2, 4, 6}, {0, 3, 6}, {1, 4, 7}, {2, 5, 8}]
for position in winningPositions:
if position.issubset(self.playerPosition):
self.winner = self.playerSymbol
print("Player Wins :)")
return True
elif position.issubset(self.aiPosition):
self.winner = self.aiSymbol
print("AI wins :(")
return True
if self.board.count(" ") == 0:
self.winner = "tie"
print("Guess it's a draw")
return True
return False
def findOptimalPosition(self):
bestScore = float("-Infinity")
elements = {} # desperate times call for desperate measures
for i in range(9):
if self.board[i] == " ":
self.board[i] = self.aiSymbol # AI quasi made the move here
if self.minimax(True) > bestScore:
bestScore = self.score
elements[i] = bestScore
self.board[i] = " "
return max(elements, key=lambda k: elements[k])
def minimax(self, isMaximizing):
if self.winner is not None:
return self.scoreBoard[self.winner]
if isMaximizing:
bestScore = float("-Infinity")
for i in range(9):
if self.board[i] == " ":
self.board[i] = self.aiSymbol
bestScore = max(self.minimax(False), bestScore)
self.board[i] = " "
return bestScore
else:
bestScore = float("Infinity")
for i in range(9):
if self.board[i] == " ":
self.board[i] = self.playerSymbol
bestScore = min(self.minimax(True), bestScore)
self.board[i] = " "
return bestScore
def play(self):
self.choice()
while not self.won():
if self.turn % 2 == 0:
pos = int(input("Where would you like to play? (0-8) "))
self.playerPosition.append(pos)
self.board[pos] = self.playerSymbol
self.turn += 1
self.drawBoard()
else:
aiTurn = self.findOptimalPosition()
self.aiPosition.append(aiTurn)
self.board[aiTurn] = self.aiSymbol
self.turn += 1
print("\n")
print("\n")
self.drawBoard()
else:
print("Thanks for playing :)")
tictactoe = TicTacToe()
tictactoe.play()
I come from a java background and am not used to this :( Any help would be highly appreciated
I am open to suggestions and ways to improve my code and fix this problem. Thanks in advance and stay healthy, Kristi
I am posting this as an answer, just in case somebody in the future stumbles upon the same problem :)
the main issue i encountered (besides my bad programming style) is that i forgot to update the contents the lists playerPosition and aiPosition. You can review the rest of the changes in the working code:
class TicTacToe:
def __init__(self):
self.board = [" ", " ", " ", " ", " ", " ", " ", " ", " "]
self.playerSymbol = ""
self.playerPosition = []
self.aiSymbol = ""
self.aiPosition = []
self.winner = None
self.scoreBoard = None
self.turn = 0
self.optimalMove = int()
def drawBoard(self):
print(self.board[0] + " | " + self.board[1] + " | " + self.board[2])
print("___" + "___" + "___")
print(self.board[3] + " | " + self.board[4] + " | " + self.board[5])
print("___" + "___" + "___")
print(self.board[6] + " | " + self.board[7] + " | " + self.board[8])
def choice(self):
answer = input("What do you want to play as? (type x or o) ")
if answer.upper() == "X":
self.playerSymbol = "X"
self.aiSymbol = "O"
else:
self.playerSymbol = "O"
self.aiSymbol = "X"
self.scoreBoard = {
self.playerSymbol: -1,
self.aiSymbol: 1,
"tie": 0
}
def availableMoves(self):
moves = []
for i in range(0, len(self.board)):
if self.board[i] == " ":
moves.append(i)
return moves
def won_print(self):
self.won()
if self.winner == self.aiSymbol:
print("AI wins :(")
exit(0)
elif self.winner == self.playerSymbol:
print("Player Wins :)")
exit(0)
elif self.winner == "tie":
print("Guess it's a draw")
exit(0)
def won(self):
winningPositions = [{0, 1, 2}, {3, 4, 5}, {6, 7, 8},
{0, 4, 8}, {2, 4, 6}, {0, 3, 6},
{1, 4, 7}, {2, 5, 8}]
for position in winningPositions:
if position.issubset(self.playerPosition):
self.winner = self.playerSymbol
return True
elif position.issubset(self.aiPosition):
self.winner = self.aiSymbol
return True
if self.board.count(" ") == 0:
self.winner = "tie"
return True
self.winner = None
return False
def set_i_ai(self, i):
self.aiPosition.append(i)
self.board[i] = self.aiSymbol
def set_clear_for_ai(self, i):
self.aiPosition.remove(i)
self.board[i] = " "
def set_i_player(self, i):
self.playerPosition.append(i)
self.board[i] = self.playerSymbol
def set_clear_for_player(self, i):
self.playerPosition.remove(i)
self.board[i] = " "
def findOptimalPosition(self):
bestScore = float("-Infinity")
elements = {} # desperate times call for desperate measures
for i in self.availableMoves():
self.set_i_ai(i)
score = self.minimax(False)
if score > bestScore:
bestScore = score
elements[i] = bestScore
self.set_clear_for_ai(i)
if bestScore == 1:
print("you messed up larry")
elif bestScore == 0:
print("hm")
else:
print("whoops i made a prog. error")
return max(elements, key=lambda k: elements[k])
def minimax(self, isMaximizing):
if self.won():
return self.scoreBoard[self.winner]
if isMaximizing:
bestScore = float("-Infinity")
for i in self.availableMoves():
self.set_i_ai(i)
bestScore = max(self.minimax(False), bestScore)
self.set_clear_for_ai(i)
return bestScore
else:
bestScore = float("Infinity")
for i in self.availableMoves():
self.set_i_player(i)
bestScore = min(self.minimax(True), bestScore)
self.set_clear_for_player(i)
return bestScore
def play(self):
self.choice()
while not self.won_print():
if self.turn % 2 == 0:
pos = int(input("Where would you like to play? (0-8) "))
self.playerPosition.append(pos)
self.board[pos] = self.playerSymbol
self.turn += 1
self.drawBoard()
else:
aiTurn = self.findOptimalPosition()
self.aiPosition.append(aiTurn)
self.board[aiTurn] = self.aiSymbol
self.turn += 1
print("\n")
print("\n")
self.drawBoard()
else:
print("Thanks for playing :)")
if __name__ == '__main__':
tictactoe = TicTacToe()
tictactoe.play()
But as mentioned, the code may work, but there are MANY problems regarding the logic and structure, so do not straight-forward copy-paste it :))