I have been trying to improve my understanding of python by programming small games, such as tic tac toe. I created a copy of the game from scratch, but then went off to find a way of creating a reasonable ai for the game. I decided to use minimax to achieve this goal. I found a tutorial for the algorithm and attempted to mould it for the game.
However when the code is run, on the ai's first turn. Every empty space left on the board is filled with the same symbol, forcing a win, making the game unplayable.
As I was unfamiliar and inexperienced with the algorithm, I took the code from a youtube tutorial and edited it so that it was functional for the game.
Here is the code
import random
import time
import sys
from sys import maxsize
#converts numbers from the board to X O and "" for printing out the board
def numToSymbol(board):
visual = board
for i in range(0, 9):
if visual[i] == -1:
visual[i]= "X"
elif visual[i] == 1:
visual[i] = "O"
elif visual[i] == 0:
visual[i] = " "
return visual
def symbolToNum(visual):
board = visual
for i in range(0, 9):
if board[i] == "X":
board[i] = -1
elif board[i] == "O":
board[i] = 1
elif board[i] == " ":
board[i] = 0
return board
# prints the board, first coverting numbers throught numtoSymbol
def drawBoard():
visual = numToSymbol(board)
print(
"|"+ str(visual[0]) + "|" + str(visual[1]) + "|" + str(visual[2]) + "| \n"
"-------\n"
"|"+ str(visual[3]) + "|" + str(visual[4]) + "|" + str(visual[5]) + "| \n"
"-------\n"
"|"+ str(visual[6]) + "|" + str(visual[7]) + "|" + str(visual[8]) + "| \n"
"-------")
symbolToNum(visual)
# checks the possible options for 3 in a row and if any are all held by one side returns true
def checkWin(board, winConditions, ai):
if ai == True:
win = 3
if ai == False:
win = -3
for row in winConditions:
checkA = board[row[0]]
checkB = board[row[1]]
checkC = board[row[2]]
if checkA + checkB + checkC == int(win):
return True
return False
def checkDraw(board):
emptyTile = 9
for tile in board:
if tile != 0:
emptyTile -= 1
if emptyTile == 0:
completion(2)
def availableMoves(board, bonus):
availableSlots = []
for position in range(0,9):
if board[position] == 0:
availableSlots.append(position + bonus)
return availableSlots
def playerTurn(board, remainingTurns):
board = board
checkDraw(board)
visual =drawBoard()
print("pick one of the available slots \n")
availableSlots = availableMoves(board, 1)
print(availableSlots)
choice = int(input('Select a tile from those shown above:\n')) -1
while True:
if 0 <= choice <= 8:
if board[choice] == 0:
board[choice] = -1
break
else:
choice = int(input('Select a tile from those shown above which has not already been selected:\n')) -1
else:
choice = int(input('Select a tile from those shown above:\n')) -1
visual = drawBoard()
if checkWin(board, winConditions, False) == True:
completion(0)
else:
aiTurn(board, remainingTurns - 1)
class Node(object):
def __init__(self, remainingTurns, playerNum, board, value = 0):
self.depth = remainingTurns
self.playerNum = playerNum
self.board = board
self.value = value
self.moves = availableMoves(self.board, 0)
self.children = []
self.createChildren()
def availableMoves(self, board):
self.availableSlots = []
for position in range(0,9):
if board[position] == 0:
availableSlots.append(position)
return self.availableSlots
def winCheck(self, state, playerNum):
self.winConditions = [[0, 1, 2],[3, 4, 5],[6, 7, 8],[0, 3, 6],[1, 4, 7],[2, 5, 8],[0, 4, 8],[2, 4, 6]]
self.win = 3
for row in self.winConditions:
self.checkA = self.state[row[0]]
self.checkB = self.state[row[1]]
self.checkC = self.state[row[2]]
if self.checkA + self.checkB + self.checkC == int(self.win * self.playerNum):
return True
return False
def createChildren(self):
if self.depth > 0:
for i in self.moves:
self.state = self.board
self.state[i] = self.playerNum
print(board)
self.children.append(Node(self.depth - 1, self.playerNum * -1, self.state, self.realVal(self.state, self.playerNum) ))
def realVal(self, value, playerNum):
value = self.winCheck(self.state, self.playerNum)
if value == True:
return maxsize * self.playerNum
else:
return 0
def minimax(node, depth, playerNum):
if depth == 0 or abs(node.value) == maxsize:
return node.value
bestValue = maxsize * -playerNum
for i in range(len(node.children)):
child = node.children[i]
val = minimax(child, depth - 1, -playerNum)
if (abs(maxsize * playerNum - val) < abs(maxsize * playerNum - bestValue)):
bestValue = val
return bestValue
def aiTurn(board, remainingTurns):
checkDraw(board)
print('Waiting for ai')
time.sleep(2)
board = board
state = board
currentPlayer = 1
tree = Node(remainingTurns, currentPlayer, state)
bestChoice = -100
bestValue = maxsize * -1
for i in range(len(tree.children)):
n_child = tree.children[i]
i_val = minimax(n_child, remainingTurns, -currentPlayer,)
if (abs(currentPlayer * maxsize - i_val) <= abs(currentPlayer * maxsize - bestValue)):
bestValue = i_val
bestChoice = i
print(bestChoice)
print(board)
#choice = minimax(tree, remainingTurns, 1)
board[bestChoice] = 1
print(board)
if checkWin(board, winConditions, True) == True:
completion(1)
else:
playerTurn(board, remainingTurns - 1)
def completion(state):
if state == 1:
print('The computer has won this game.')
choice = str(input('press y if you would like to play another game; Press n if you would not \n'))
if choice == 'y' or choice == 'Y':
playGame()
else:
sys.exit()
if state == 0:
print('you win!')
choice = str(input('press y if you would like to play another game; Press n if you would not \n'))
if choice == 'y' or choice == 'Y':
playGame()
else:
sys.exit()
if state == 2:
print('you drew')
choice = str(input('press y if you would like to play another game; Press n if you would not \n'))
if choice == 'y' or choice == 'Y':
playGame()
else:
sys.exit()
def playGame():
global board
board = [0,0,0,0,0,0,0,0,0]
global winConditions
winConditions = [
[0, 1, 2],
[3, 4, 5],
[6, 7, 8],
[0, 3, 6],
[1, 4, 7],
[2, 5, 8],
[0, 4, 8],
[2, 4, 6]
]
global remainingTurns
remainingTurns = 9
playerFirst = random.choice([True, False])
if playerFirst == True:
playerTurn(board, remainingTurns)
else:
aiTurn(board, remainingTurns)
if __name__ == '__main__':
playGame()
This is the output from the above code
[1, 0, 0, 0, 0, 0, 0, 0, 0]
[1, -1, 0, 0, 0, 0, 0, 0, 0]
[1, -1, 1, 0, 0, 0, 0, 0, 0]
[1, -1, 1, -1, 0, 0, 0, 0, 0]
[1, -1, 1, -1, 1, 0, 0, 0, 0]
[1, -1, 1, -1, 1, -1, 0, 0, 0]
[1, -1, 1, -1, 1, -1, 1, 0, 0]
[1, -1, 1, -1, 1, -1, 1, -1, 0]
[1, -1, 1, -1, 1, -1, 1, -1, 1]
[1, -1, 1, -1, 1, -1, 1, -1, -1]
[1, -1, 1, -1, 1, -1, 1, 1, -1]
[1, -1, 1, -1, 1, -1, 1, 1, 1]
[1, -1, 1, -1, 1, -1, -1, 1, 1]
[1, -1, 1, -1, 1, -1, -1, -1, 1]
[1, -1, 1, -1, 1, -1, -1, -1, -1
[1, -1, 1, -1, 1, 1, -1, -1, -1]
[1, -1, 1, -1, 1, 1, 1, -1, -1]
[1, -1, 1, -1, 1, 1, 1, 1, -1]
[1, -1, 1, -1, 1, 1, 1, 1, 1]
[1, -1, 1, -1, -1, 1, 1, 1, 1]
[1, -1, 1, -1, -1, -1, 1, 1, 1]
[1, -1, 1, -1, -1, -1, -1, 1, 1]
[1, -1, 1, -1, -1, -1, -1, -1, 1
[1, -1, 1, -1, -1, -1, -1, -1, -
[1, -1, 1, 1, -1, -1, -1, -1, -1
[1, -1, 1, 1, 1, -1, -1, -1, -1]
[1, -1, 1, 1, 1, 1, -1, -1, -1]
[1, -1, 1, 1, 1, 1, 1, -1, -1]
[1, -1, 1, 1, 1, 1, 1, 1, -1]
[1, -1, 1, 1, 1, 1, 1, 1, 1]
[1, -1, -1, 1, 1, 1, 1, 1, 1]
[1, -1, -1, -1, 1, 1, 1, 1, 1]
[1, -1, -1, -1, -1, 1, 1, 1, 1]
[1, -1, -1, -1, -1, -1, 1, 1, 1]
[1, -1, -1, -1, -1, -1, -1, 1, 1
[1, -1, -1, -1, -1, -1, -1, -1,
[1, -1, -1, -1, -1, -1, -1, -1,
[1, 1, -1, -1, -1, -1, -1, -1, -
[1, 1, 1, -1, -1, -1, -1, -1, -1
[1, 1, 1, 1, -1, -1, -1, -1, -1]
[1, 1, 1, 1, 1, -1, -1, -1, -1]
[1, 1, 1, 1, 1, 1, -1, -1, -1]
[1, 1, 1, 1, 1, 1, 1, -1, -1]
[1, 1, 1, 1, 1, 1, 1, 1, -1]
[1, 1, 1, 1, 1, 1, 1, 1, 1]
8
[1, 1, 1, 1, 1, 1, 1, 1, 1]
[1, 1, 1, 1, 1, 1, 1, 1, 1]
The computer has won this game.
Any suggestions?
Problem lies when you init your node you just copy the ref of board:
self.board = board
whereas you should copy the values
self.board = board[::]
Else all your Node objects refer to the same board: the global one.