ABPruningTTT.py

#Instead of x and o players are 1 and -1


def eval(board): #returns 1 if player 1 wins, 0 if no player wins, -1 if player -1 wins
  for i in range(3):
    if board[i*3] == board [i*3 + 1] == board[i*3 +2] and board[i*3]!=0: #Horizontal
      return board[i*3]
    if board[i] == board[i+3] == board [i+6] and board[i*3]!=0: #Vertical
      return board[i]
  if board[0] == board[4] == board[8] and board[0]!=0: #Diagonal 1
     return board[0]
  if board[2] == board[4] == board[6] and board[2]!=0: #Diagonal 2
    return board[2]
  return 0 #Otherwise

def moves(board): #Gets all possible moves by index 0-8 inclusive
  mv = []
  for i in range(len(board)):
    if (board[i] == 0):
      mv.append(i)
  return mv

def alphabeta(node, depth, a, b, player): 
    if len(moves(node)) == 0 or eval(node) !=0 or depth==9: #Terminal Conditions
        return eval(node)
    if player == 1:
        value = -3 #Arbitrary, must be below -1 but doesn't really matter for tic tac toe.
        for i in moves(node): #Try all moves
            tboard = board.copy()
            tboard[i] = player #Add move tp board
            value = max(value, alphabeta(tboard, depth + 1, a, b, player*-1)) #Minimax type thing
            if value > b: #Prune the tree 
                break
            a =  max(a, value)
        return value
    else:
        value = 3
        for i in moves(node):
            tboard = board.copy()
            tboard[i] = player
            value = min(value, alphabeta(tboard, depth + 1, a, b, player*-1))
            if value < a:
                break
            b = min(b, value)
        return value


def ab_get_best_move(board,player):
  t_score = -1
  best_move = moves(board)[0]
  for i in moves(board):
    tboard = board.copy()
    tboard[i] = player
    score = alphabeta(tboard,0,-2,2,-player) * player
    if score > t_score:
      best_move = i
      t_score =  score
  return best_move,t_score


board = [1,-1,0,
         1,-1,0,
         0 ,0,0]
ab_get_best_move(board,1)

wow! amazing code