code detail

"""tic tac toe for 2 players, wit win checking"""
# ----- defnine some top-level variables ------
cells = [[" " for x in range(3)] for y in range(3)]
symbols = ("x", "o")      # tuples are read-only
greeting = "This is turn {}. Player {}, where do you put your '{}'?"
text = "Please enter coordinate (0 or 1 or 2) for column and row like for example: 1 2 and press ENTER >>>"


# ---- functions ----
def check_win(char):
    """checks the array cells and returns True if 3 chars build a line"""
    for row in range(3):  # checking rows. range(3) returns 0, 1, 2, it is the same as 'for row in [0,1,2]:'
        if cells[row][0] == char and cells[row][1] == char and cells[row][2] == char:
            return True  # checking columns
    for col in range(3):
        if cells[0][col] == char and cells[1][col] == char and cells[2][col] == char:
            return True
    # checking diagonal

…

        if is_free(row, column):
            print("input accepted")
            cells[int(raw_row)][int(raw_column)] = player_char
            break
    if check_win(player_char):  # only the active player is checked
        print(" -*- -*- -*- Congratulation, You have won, player {} -*- -*- -*-".format(player))
        display()  # final
        break
    print("*** next turn! *****")
print("Game Over")

full code

"""tic tac toe for 2 players, wit win checking"""
# ----- defnine some top-level variables ------
cells = [[" " for x in range(3)] for y in range(3)]
symbols = ("x", "o")      # tuples are read-only
greeting = "This is turn {}. Player {}, where do you put your '{}'?"
text = "Please enter coordinate (0 or 1 or 2) for column and row like for example: 1 2 and press ENTER >>>"


# ---- functions ----
def check_win(char):
    """checks the array cells and returns True if 3 chars build a line"""
    for row in range(3):  # checking rows. range(3) returns 0, 1, 2, it is the same as 'for row in [0,1,2]:'
        if cells[row][0] == char and cells[row][1] == char and cells[row][2] == char:
            return True  # checking columns
    for col in range(3):
        if cells[0][col] == char and cells[1][col] == char and cells[2][col] == char:
            return True
    # checking diagonal
    if cells[0][0] == char and cells[1][1] == char and cells[2][2] == char:
        return True
    if cells[2][0] == char and cells[1][1] == char and cells[0][2] == char:
        return True
    return False  # all win condition checked without success, therefore no win


def is_free(row, column):
    """checks a single coordinate in the the cells array returns True if the cell is free (contains a Space)
    otherwise returns False"""
    try:
        content = cells[row][column]
    except IndexError:
        print("this cell does not exist")
        return False
    return True if content == " " else False


def display():
    """displays the 3x3 array 'cells' with heading row and column"""
    print("r\c 0:  1:  2:")  # header line
    for index, row in enumerate(cells):
        print("{}: ".format(index), end="")  # header column
        for element in row:
            print("[{}] ".format(element), end="")
        print()  # force new line

# ---- the 'main loop' of the game -----
for turns in range(9):  # play 9 legal moves, then the board is full
    display()
    player = turns % 2  # modulo: the remainder of a division by 2.
    player_char = symbols[player]
    print(greeting.format(player, turns, player_char))
    while True:  # ask until legal move
        command = input(text)
        command = command.strip()
        try:
            raw_column, raw_row = command[0], command[-1]  # 2 variables, 2 values
        except:
            print("Enter 2 coordinates. Try again")
            continue  # go back to the start of the while loop
        try:
            row = int(raw_row)
            column = int(raw_column)
        except ValueError:
            print("Enter numbers only. Try again")
            continue  # go back to the start of the while loop
        if is_free(row, column):
            print("input accepted")
            cells[int(raw_row)][int(raw_column)] = player_char
            break
    if check_win(player_char):  # only the active player is checked
        print(" -*- -*- -*- Congratulation, You have won, player {} -*- -*- -*-".format(player))
        display()  # final
        break
    print("*** next turn! *****")
print("Game Over")

diff

code discussion

• line 10: The check_win() functions needs the string char as argument and only checks if this char string has a winning line of three occurrences at inside cells. Because cells was declared at top-level, it is not necessary to pass it as an argument to the check_win() function.
• line 12: Testing for 3 chars in a row could also be done by use of python's built-in all function (see paragraph below)
• line 12-17: This code is a bit long and will be improved in step005.
• line 9-69: no changes since the previous version, see code discussion in step004
• line 69: breaks out of the inner while loop (line 52).
• line 70: calling the check_win() function with the correct char for the actual player.
• line 73: breaks out of the outer for loop (line 47)

output

r\c 0:  1:  2:
0: [ ] [ ] [ ] 
1: [ ] [ ] [ ] 
2: [ ] [ ] [ ] 

This is turn 0. Player 0, where do you put your 'x'?
Please enter numbers (0 or 1 or 2) for column and row
   like for example: '1 2' or '02' or '2x1'
   and press ENTER >>> 00
input accepted

r\c 0:  1:  2:
0: [x] [ ] [ ] 
1: [ ] [ ] [ ] 
2: [ ] [ ] [ ] 

This is turn 1. Player 1, where do you put your 'o'?
Please enter numbers (0 or 1 or 2) for column and row
   like for example: '1 2' or '02' or '2x1'
   and press ENTER >>> 12
input accepted

r\c 0:  1:  2:
0: [x] [ ] [ ] 
1: [ ] [ ] [ ] 
2: [ ] [o] [ ] 

This is turn 2. Player 0, where do you put your 'x'?
Please enter numbers (0 or 1 or 2) for column and row
   like for example: '1 2' or '02' or '2x1'
   and press ENTER >>> 10
input accepted

r\c 0:  1:  2:
0: [x] [x] [ ] 
1: [ ] [ ] [ ] 
2: [ ] [o] [ ] 

This is turn 3. Player 1, where do you put your 'o'?
Please enter numbers (0 or 1 or 2) for column and row
   like for example: '1 2' or '02' or '2x1'
   and press ENTER >>> 22
input accepted

r\c 0:  1:  2:
0: [x] [x] [ ] 
1: [ ] [ ] [ ] 
2: [ ] [o] [o] 

This is turn 4. Player 0, where do you put your 'x'?
Please enter numbers (0 or 1 or 2) for column and row
   like for example: '1 2' or '02' or '2x1'
   and press ENTER >>> 20
input accepted

 -*- -*- -*- Congratulation, You have won, player 0 -*- -*- -*-
r\c 0:  1:  2:
0: [x] [x] [x] 
1: [ ] [ ] [ ] 
2: [ ] [o] [o] 

Game Over