first project.py

# Game board
board = ["_", "_", "_",
         "_", "_", "_",
         "_", "_", "_"]

# If game is still going
game_still_going = True

winner = None


current_player = "X"

# Display board
def display_board():
    print(board[0] + " | " + board[1] + " | " + board[2])
    print(board[3] + " | " + board[4] + " | " + board[5])
    print(board[6] + " | " + board[7] + " | " + board[8])

# Play a game of tic tac toe
def play_game():

    display_board()

# While the game is still going
    while game_still_going:

    # handle a single turn of an arbitrary player
     handle_turn(current_player)

     # Check if the game has ended
     check_if_game_over()

    # flip to the other player
     flip_player()

    if winner == "X" or winner == "O":
        print(winner + " won.")
    elif  winner == None:
        print("Tie.")

# handle a single turn of an arbitrary player
def handle_turn(player):

    print(player + "`s turn.")
    position = input("choose a position from 1 to 9: ")

    valid = False
    while not valid:

       while position not in ["1", "2", "3", "4", "5", "6", "7", "8", "9"]:
           position = input("Invalid input . Choose a position from 1-9: ")

       position = int(position) - 1

       if board[position] == "-":
         valid = True
       else:
           print("you can`t go there.Go again.")


       board[position] = player

       display_board()


def check_if_game_over():
    check_if_win()
    check_if_tie()


def check_if_win():

    global winner
    # Check rows
    row_winner = check_rows()
    # Check columns
    column_winner = check_columns()
    # check diagonals
    diagonal_winner = check_diagonals()
    if row_winner:
       winner = row_winner
    elif column_winner:
        winner = column_winner
    elif diagonal_winner:
       winner = diagonal_winner
    else:
       winner = None
    return



def check_rows():
    # Set up global variables
    global game_still_going
    # Check if row has same value
    row_1 = board[0] == board[1] == board[2] != "-"
    row_2 = board[3] == board[4] == board[5] != "-"
    row_3 = board[6] == board[7] == board[8] != "-"
    # If any row does have a match, flag there is a win
    if row_1 or row_2 or row_3:
        game_still_going = False
    # Return the winner (X or O)
        if row_1:
            return board[0]
        elif row_2:
           return board[3]
        elif row_3:
           return board[6]
    return


def check_columns():
    global game_still_going
    column_1 = board[0] == board[3] == board[6] != "_"
    column_2 = board[1] == board[4] == board[7] != "_"
    column_3 = board[2] == board[5] == board[8] != "_"
 # If any column does have a match, flag there is a win
    if column_1 or column_2 or column_3:
        game_still_going = False
 # Return the winner (X or O)
        if column_1:
            return board[0]
        elif column_2:
            return board[1]
        elif column_3:
            return board[2]
    return


def check_diagonals():
 # Set up global variables
    global game_still_going
    diagonals_1 = board[0] == board[4] == board[8] != "_"
    diagonals_2 = board[6] == board[4] == board[2] != "_"

    if diagonals_1 or diagonals_2:
        game_still_going = False
        # Return the winner (x or 0)
        if diagonals_1:
            return board[0]
        elif diagonals_2:
            return board[6]
    return


def check_if_tie():
    global game_still_going
    if "_" not in board:
       game_still_going = False
    return

def flip_player():
    global current_player
    if current_player == "X":
        current_player = "O"
    elif current_player == "O":
        current_player = "X"
    return


play_game()