Build a TicTacToe class for two players, X and O, on a 3 by 3 board. One object is one game: it remembers the board and whose turn it is, lets the players take turns, and tells who has won.
The board: rows and columns are numbered 0, 1 and 2. Cell (0, 0) is the top-left corner, (0, 2) the top-right, (2, 0) the bottom-left and (2, 2) the bottom-right. A cell holds 'X', 'O' or '.' when it is still empty.
Build:
- A new game. The constructor
__init__(self)stores the board as a list of three rows (each row a list of three'.') inself.board, andself.player = 'X'. Every row must be its own list (do not write[['.'] * 3] * 3, which repeats one row three times). All nine cells are empty and X moves first. move(self, r, c)plays one turn at the given row and column (always between 0 and 2, so you do not need to check the range).- If the cell is not empty, ignore the call: nothing changes and it is still the same player's turn.
- Otherwise put the current player's mark in the cell, then give the turn to the other player (X becomes O, O becomes X).
winner(self)returns the winner as a one-character string:'X','O'or'.'.- A player wins by having the same mark in all three cells of a row, a column, or one of the two diagonals ((0,0), (1,1), (2,2) and (0,2), (1,1), (2,0)). Three empty cells in a line are not a win.
- If nobody has three in a row, return
'.'. That covers a game still in progress, an empty board and a draw.
You start with this code, which plays six games and prints the result of each one:
game = TicTacToe()
game.move(0, 0)
game.move(1, 0)
game.move(0, 1)
game.move(1, 1)
game.move(0, 2)
print(game.winner() + " wins!")
game = TicTacToe()
game.move(0, 0)
game.move(0, 1)
game.move(0, 0)
game.move(1, 0)
game.move(1, 1)
game.move(2, 2)
game.move(2, 1)
print(game.winner() + " wins!")
game = TicTacToe()
game.move(0, 0)
game.move(0, 1)
game.move(1, 1)
game.move(0, 2)
game.move(2, 2)
print(game.winner() + " wins!")
game = TicTacToe()
game.move(0, 2)
game.move(0, 0)
game.move(1, 1)
game.move(0, 1)
game.move(2, 0)
print(game.winner() + " wins!")
game = TicTacToe()
game.move(0, 0)
game.move(0, 1)
game.move(0, 2)
game.move(1, 1)
game.move(1, 0)
game.move(1, 2)
game.move(2, 1)
game.move(2, 0)
game.move(2, 2)
print("No winner: " + game.winner())
game = TicTacToe()
print("No winner: " + game.winner())
Games played: X fills the top row; then a game where X tries to play on a cell that is already taken (ignored, and still X's turn) and O wins the middle column; X on the main diagonal; X on the other diagonal; a full board with no three in a row; and a brand-new game.
Expected output:
X wins! O wins! X wins! X wins! No winner: . No winner: .
There are eight winning lines: three rows, three columns and two diagonals. A loop over
i from 0 to 2 can check row i and column i together; the two diagonals come after the loop. Skip a line whose first cell is empty.
Check for a taken cell first and leave the move method before touching the board or the turn. Only a successful move passes the turn to the other player.
class TicTacToe:
def __init__(self):
self.board = []
for i in range(3):
self.board.append(['.'] * 3)
self.player = 'X'
def move(self, r, c):
if self.board[r][c] != '.':
return
self.board[r][c] = self.player
if self.player == 'X':
self.player = 'O'
else:
self.player = 'X'
def winner(self):
b = self.board
for i in range(3):
if b[i][0] != '.' and b[i][0] == b[i][1] and b[i][1] == b[i][2]:
return b[i][0]
if b[0][i] != '.' and b[0][i] == b[1][i] and b[1][i] == b[2][i]:
return b[0][i]
if b[0][0] != '.' and b[0][0] == b[1][1] and b[1][1] == b[2][2]:
return b[0][0]
if b[0][2] != '.' and b[0][2] == b[1][1] and b[1][1] == b[2][0]:
return b[0][2]
return '.'
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