# Beginner python tic tac toe with AI

I've come up with this code for a tic tac toe game with and AI that the player can go against, please help me optimise my code and help me grow better habits haha.

import random                  # I want 'random' so I can randomize the AI's choices
# whenever it cant win or 'intercept' the player
board_tiles = ['-', '-', '-',
'-', '-', '-',          # Here I declare some variables globaly
'-', '-', '-']          # so i can use them later
board_rows = ''
board_columns = ''
board_diagonals = ''
board_layout = ''
def board_update():
global board_rows, board_columns, board_diagonals, board_layout      # In this function I update the variables above
board_rows = [(board_tiles[0], board_tiles[1], board_tiles[2]),      # this is called all the time in the program so
(board_tiles[3], board_tiles[4], board_tiles[5]),      # that the game knows exactly how is the board
(board_tiles[6], board_tiles[7], board_tiles[8])]      # at all times
board_columns = [(board_tiles[0], board_tiles[3], board_tiles[6]),
(board_tiles[1], board_tiles[4], board_tiles[7]),
(board_tiles[2], board_tiles[5], board_tiles[8])]
board_diagonals = [(board_tiles[0], board_tiles[4], board_tiles[8]),
(board_tiles[2], board_tiles[4], board_tiles[6])]
board_layout = ''' {} | {} | {}
{} | {} | {}
{} | {} | {}'''.format(board_tiles[0], board_tiles[1], board_tiles[2], board_tiles[3], board_tiles[4],
board_tiles[5], board_tiles[6], board_tiles[7], board_tiles[8])
def board_display():
board_update()            # Here I make a function to display the board
print('-----------')      # I declare it because it's used a lot
print(board_layout)

def check_if_tie():
board_update()
if '-' not in board_tiles and check_winner() is None:     # These two functions are needed to check if the game tied
return True                                           # or if there is a winner, and if there is, if it's the AI
else:                                                     # or the player. The 'tie' one can either return True or
return False                                          # False, and the 'winner' one can return 'X' or 'O'
# depending on which won the game
def check_winner():                                           # ('X' being the player and 'O' being the AI)
board_update()
for i in board_rows + board_columns + board_diagonals:
if i.count('X') == 3:
return 'X'
elif i.count('O') == 3:
return 'O'
return None

def player_turn():
board_update()                                                       # In this function I get the input from the
selected_tile = int(input('Select a tile (1 - 9): ')) - 1            # player in the form of a number (1 - 9),
while board_tiles[selected_tile] != '-':                             # the numbers refer to the tiles on the board
selected_tile = int(input('Insert another tile (1 - 9): ')) - 1  # as seen on the right:        1 | 2 | 3
board_tiles[selected_tile] = 'X'                                     # There's a section that       4 | 5 | 6
# checks if the input is       7 | 8 | 9
def ai_tile():                                                           # valid (if the tile is already occupied)
intercept_tile = 0
win_tile = 0
for row in board_rows:
if row.count('O') == 2 and row.count('X') == 0:           # This function is needed so the AI can know where
for i in row:                                         # to place it's tile, his decision can be:
if i == '-':                                      # - To end the game if it's possible.
return win_tile                               # - To 'intercept' the player from winning.
win_tile += 1                                     # - To randomly select a tile.
win_tile += 3                                             # (this is the hierarchy of it's decisions, meaning
win_tile = 0                                                  #  that the AI will prefer to win the game over
for column in board_columns:                                  #  intercepting the player or playing randomly)
if column.count('O') == 2 and column.count('X') == 0:
for i in column:                                      # The function checks for a row, column or diagonal
if i == '-':                                      # that either has 2 'O' and no 'X' or for one that
return win_tile                               # has 2 'X' and no 'O', so that it can either 'win'
win_tile += 3                                     # or intercept the player from winning, if none
win_tile += 1                                             # meets this condition, then it picks a tile randomly
win_tile = 0
x = 4                                                         # The 'x' variable that is local to this function is
for diagonal in board_diagonals:                              # used to keep track of the tile in which the AI has
if diagonal.count('O') == 2 and diagonal.count('X') == 0: # to win or intercept the player in diagonals, my
for i in diagonal:                                    # idea was that for each diagonal, the number of tiles
if i == '-':                                      # that are needed to be skipped are different
return win_tile                               # (in the first iteration of the loop 'x' is 4, meaning
win_tile += x                                     # that the tiles jump from 1 to 5 to 9, in the second
x -= 2                                                    # iteration, 'x' is 2, then the tiles jump from 3 to 5
win_tile += x                                             # to 7, 1 - 5 - 9 and 3 - 5 - 7 being the diagonals)

for row in board_rows:
if row.count('X') == 2 and row.count('O') == 0:
for i in row:
if i == '-':
return intercept_tile
intercept_tile += 1
intercept_tile += 3
intercept_tile = 0
for column in board_columns:
if column.count('X') == 2 and column.count('O') == 0:
for i in column:
if i == '-':
return intercept_tile
intercept_tile += 3
intercept_tile += 1
intercept_tile = 0
x = 4
for diagonal in board_diagonals:
if diagonal.count('X') == 2 and diagonal.count('O') == 0:
for i in diagonal:
if i == '-':
return intercept_tile
intercept_tile += x
x -= 2
intercept_tile += x
random_tile = random.randint(0, 8)
while board_tiles[random_tile] != '-':         # Here it decides to randomly choose a tile.
random_tile = random.randint(0, 8)
return random_tile

def ai_turn():                                     # In this funcion, I did all the aesthetics of the ai turn
board_update()                                 # like printing which tile it chose and everything
print('-----------')                           # 'ai_tile()' is used here, and it returns the tile that
ai_choice = ai_tile()                          # the AI picked.
board_tiles[ai_choice] = 'O'
print('AI chooses tile {}'.format(ai_choice + 1))
def game():
while check_winner() is None and check_if_tie() is False:
board_display()                                          # This function is the main one, it checks if
player_turn()                                            # the game is over, sequences the turns,
if check_winner() is None and check_if_tie() is False:   # displays the board and announces the winner.
ai_turn()
else:
break
if check_winner() is 'X':
board_display()
print('The player won!')
print('-----------')
else:
board_display()
print('The AI won!')
print('-----------')
game()

• Can you indicate what version of python you're using? – Linny Jan 9 at 22:38
• I believe its python3.x that I used – Tlomoloko Jan 9 at 22:46
• habits are important in programming. Keep commenting your code with motivation for pieces of code. – greybeard Jan 10 at 3:19

The really big suggestion (which I'm sure you're going to hear a lot) is to not use global variables. Declaring global constants is fine, but when you have state that any function might modify at any time it rapidly gets hard to figure out what state your app is in at any given point.

So with that in mind, your board_update function should not exist. I see that the main point of it is to be able to identify the board spaces that make up a win condition. Here's how you could restructure that logic to not rely on global variables:

from random import choice
from typing import List, Optional

winning_rows = [
# horizontal
(0, 1, 2),
(3, 4, 5),
(6, 7, 8),
# vertical
(0, 3, 6),
(1, 4, 7),
(2, 5, 8),
# diagonal
(0, 4, 8),
(2, 4, 6),
]

def check_winner(board: List[str]) -> Optional[str]:
"""Return the winning player (if any).
Players are 'X' (human) and 'O' (computer)."""
for player in ['X', 'O']:
for row in winning_rows:
if all([board[space] == player for space in row]):
return player
return None

def ai_move(board: List[str]) -> int:
"""Compute the best move for player 'O' (the AI)."""

def winning_move(
player: str,
opponent: str
) -> Optional[int]:
"""Return the winning move for the given player vs the opponent,
or None if there's no winning move."""
for spaces in winning_rows:
row = [board[space] for space in spaces]
if row.count(player) == 2 and not opponent in row:
return next(s for s in spaces if board[s] != player)
return None  # no winning move

# Check to see if there's a move that would win the game for O.
move = winning_move(board, 'O', 'X')
if move is not None:
return move  # Winner!

# Check to see if there's a move that would win the game for X.
move = winning_move(board, 'X', 'O')
if move is not None:
return move  # Blocked!

# Otherwise make a random move.
return choice([
space for space in range(len(board)) if board[space] not in ('O', 'X')
])


Note that the board itself (because it will change) should not be a global, but the set of winning_rows can be a global constant since it's defined by the rules of the game rather than a particular game in progress.

• Yeah, thanks, but then instead of having my board_rows, board_columns and board_diagonals, I would have only this ''winning_rows'' list? – Tlomoloko Jan 9 at 23:09
• Yes -- I don't think you need to have them separated into different variables, since they're all treated equally (i.e. any one of them defines a win). I didn't look too hard at your ai_tile function but I'm pretty sure it doesn't need to separate them out either -- if you're stuck on a clean way to implement that I could take another look at it. – Samwise Jan 10 at 0:27
• btw the thing of doing your comment in a "column" next to the code is not great for reasons that will rapidly become obvious as you edit the code :P – Samwise Jan 10 at 0:45
• in my ai_tile i have to keep track of the tile that i need the AI to choose, and for that it skips 1, 2, 3 or even 4 tiles from the board_tiles so that i can stay on that row, column or diagonal, i thought of putting them all in a joined list but then for each iteration i would have to have a different number to add or subtract, idk if i explained it clearly, but i have a more detailed explanation on that in my comments on the code – Tlomoloko Jan 10 at 1:54
• Typing is something you should absolutely learn if you want to write better code, yes. :) When you use types you can use mypy to automatically catch bugs: mypy-lang.org – Samwise Jan 10 at 16:05