This is an OpenAI gym environment for playing Tic Tac Toe (or Noughts and Crosses).
pip install tictactoe_gym
Each player takes it in turn to mark a position in a square grid (e.g., 3x3), until they form a horizontal, vertical or diagonal line across the grid (e.g., 3 in a row), in which case they win. If no further moves can be made and there is no winner then the game is a draw.
The action is an integer which can take values
For example, action 4 is the centre position,
The observation is a ndarray with shape (n, n), where n is the grid size. Each entry can take the following values:
| Value | Meaning |
|---|---|
| 0 | No mark here yet, free to mark |
| 1 | Player 1 has placed a mark here |
| -1 | Player 2 has placed a mark here |
A reward of +1 is given to the winning player with a reward of -1 for the losing player. If it's a draw both players get a reward of 0.
The episode ends if any one of the following occurs:
- Termination: A player gets
$n$ successive marks in a row, column or diagonal for an$n \times n$ grid. - Termination: No more moves can be played (i.e., every grid position is marked).
gym.make('tictactoe-v0')
No additional arguments are currently supported.
size (int): The size of the grid.
observation_space (gym.spaces.Box): The observation space, an
action_space (gym.spaces.Discrete): The action space, an
reward_range (int): The reward range, -1 for a loss, 0 for a draw, +1 for a win.
_player (int): The current player, 1/-1.
_state_size (tuple): A (1, 3) tuple of the state size - (size, size, 1).
_action_to_index_map (dict): A mapping from actions to indices, e.g., {0: [0, 0], 1: [0, 1], 2: [0, 2], 3: [1, 0], ..., 8: [2, 2]}.
_history (list) : The history of actions, e.g., [0, 5, 1, 3, 2].
_terminal (bool): Whether the game is finished or not.
_winner (int): The winning player, 1 for player 1, -1 for player 2 and 0 for a draw.
init: Initialises environment and all attributes.
get_observation: Gets the observation for a player.
get_actions: Get possible actions, i.e., positions where marks have not yet been made.
get_result: Get result for a player. If the player is 1/-1 and winner is 1/-1, then return 1, as the requested player has won. Otherwise if the player is 1/-1 and winner is -1/1, then return -1, as the player has lost. If a draw, then self._winner is 0, so returns 0.
_get_action_to_index_map: Returns the action_to_index_map. This is more efficient as it saves having to compute indices every time.
_is_valid_action: Checks an action is valid.
_row_winner: Returns winner of any row from an observation.
_col_winner: Returns winner of any column from an observation.
_main_diag_winner: Returns winner of main diagonal from an observation.
_reverse_main_diag_winner: Returns winner of reverse main diagonal from an observation.
_is_game_over: Returns true if game is over and false otherwise. Also sets the winning player as the _winner or 0 for draw.
_get_info: Get information on the game.
step: Step game using action and returns new observation, winner, game over indicator, truncated (always False here) and info.
reset: Reset the game.
clone: Clone the game.
render: Renders the current observation in the terminal as a string.