tic tac toe. assumes you're running python 3.

main.py

import sys
import random

WINNING_COMBINATIONS=[
    (1,2,3),
    (4,5,6),
    (7,8,9),
    (1,4,7), 
    (2,5,8),
    (3,6,9),
    (1,5,9),
    (3,5,7),
]

class Game:
    def __init__(self, board):
        self.board = board

    def get_player_marker(self):
        marker = ''
        while not (marker in ['X', 'O']):
            marker = input('Do you want to be X or O?').upper()
        return ('X', 'O') if marker == 'X' else ('O', 'X')  

    def check_winner(self, mark):
        grid = self.board.grid
        return any([(grid[a] == grid[b] == grid[c] == mark) for (a,b,c) in WINNING_COMBINATIONS])

    def get_player_choice(self):
        while True:
            try:
                pos = int(input('Choose your next position: (1-9)'))
                if pos in (self.board.all_positions - self.board.marked_positions):
                    return pos
                else:
                    print('Someone has already moved to that spot.')
            except ValueError:
                ...

    def play(self):
        print('Tic Tac Toe')
        human_marker, computer_marker = self.get_player_marker()
        human = True
        while True:
            if human:
                pos = self.get_player_choice()
                self.board.mark_board(human_marker, pos)
                self.board.print_board()
                if self.check_winner(human_marker):
                    print(f'Game over. Player {human_marker} wins')
                    break
            else:
                empty_positions = list(self.board.all_positions - self.board.marked_positions)
                pos = random.choice(empty_positions)
                self.board.mark_board(computer_marker, pos)
                self.board.print_board()
                if self.check_winner(computer_marker):
                    print(f'Game over. Player {computer_marker} wins')
                    break
            if self.board.is_full:
                print('Game ended in a draw')
                break
            human = not human

class Board:
    def __init__(self):
        self.grid = [' '] * 10
        self.marked_positions = set()
        self.all_positions = set(list(range(1,10)))

    def mark_board(self, marker, position):
        if self.grid[position] in ('X', 'O'):
            return
        self.grid[position] = marker
        self.marked_positions.add(position)

    @property
    def is_full(self):
        return self.marked_positions == self.all_positions

    def print_board(self):
        grid = self.grid
        sys.stdout.write('\033[H')
        sys.stdout.write('\033[J')

        print(' ' + grid[7] + ' | ' + grid[8] + ' | ' + grid[9])
        print('-----------')
        print(' ' + grid[4] + ' | ' + grid[5] + ' | ' + grid[6])
        print('-----------')
        print(' ' + grid[1] + ' | ' + grid[2] + ' | ' + grid[3])
    
def main():
    board = Board()
    game = Game(board)
    game.play()
    
if __name__ == '__main__':
    main()