Reversi
Topics Covered In This Chapter:
- The bool() Function
- Evaluating Non-Boolean Values as Booleans
How to Play Reversi
In this chapter we will make a game called Reversi. Reversi (also called Othello) is a board game that is played on a grid (so we will use a Cartesian coordinate system with XY coordinates, like we did with Sonar.) It is a game played with two players. Our version of the game will have a computer AI that is more advanced than the AI we made for Tic Tac Toe. In fact, this AI is so good that it will probably beat you almost every time you play. (I know I lose whenever I play against it!)
If you would like to see a video of Reversi being played, there is a demonstration on this book's website. Go to the URL http://inventwithpython.com/videos and find the "Reversi Demo Video" video.
Reversi has an 8 x 8 board with tiles that are black on one side and white on the other (our game will use O's and X's though). The starting board looks like Figure 15.1. Each player takes turn placing down a new tile of their color. Any of the opponent's tiles that are between the new tile and the other tiles of that color is flipped. The goal of the game is to have as many of the tiles with your color as possible. For example, Figure 15.2 is what it looks like if the white player places a new white tile on space 5, 6.
The black tile at 5, 5 is in between the new white tile and the existing white tile at 5, 4. That black tile is flipped over and becomes a new white tile, making the board look like Figure 15.3. Black makes a similar move next, placing a black tile on 4, 6 which flips the white tile at 4, 5. This results in a board that looks like Figure 15.4.
Tiles in all directions are flipped as long as they are in between the player's new tile and existing tile. Below in Figure 15.5, the white player places a tile at 3, 6 and flips black tiles in both directions (marked by the lines.) The result is in Figure 15.6.
As you can see, each player can quickly grab a majority of the tiles on the board in just one or two moves. Players must always make a move that captures at least one tile. The game ends when a player either cannot make a move, or the board is completely full. The player with the most tiles of their color wins.
The basic strategy of Reversi is to look at which move would turn over the most tiles. But you should also consider taking a move that will not let your opponent recapture many tiles after your move. Placing a tile on the sides or, even better, the corners is good because there is less chance that those tiles will end up between your opponent's tiles. The AI we make for this game will simply look for any corner moves they can take. If there are no corner moves available, then the computer will select the move that claims the most tiles.
You can learn more about Reversi from Wikipedia: http://en.wikipedia.org/wiki/Reversi
Sample Run
Notice that our version of Reversi doesn't use black and white tiles because the text that our program creates will always be the same color. Instead, we will use X's and O's to represent the human and computer players.
Welcome to Reversi!
Do you want to be X or O?
x
The player will go first.
1 2 3 4 5 6 7 8
+---+---+---+---+---+---+---+---+
| | | | | | | | |
1 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
2 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
3 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
4 | | | | X | O | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
5 | | | | O | X | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
6 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
7 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
8 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
You have 2 points. The computer has 2 points.
Enter your move, or type quit to end the game, or hints to turn
off/on hints.
53
1 2 3 4 5 6 7 8
+---+---+---+---+---+---+---+---+
| | | | | | | | |
1 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
2 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
3 | | | | | X | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
4 | | | | X | X | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
5 | | | | O | X | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
6 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
7 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
8 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
You have 4 points. The computer has 1 points.
Press Enter to see the computer's move.
...skipped for brevity...
1 2 3 4 5 6 7 8
+---+---+---+---+---+---+---+---+
| | | | | | | | |
1 | O | O | O | O | O | O | O | O |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
2 | O | O | O | O | O | O | O | O |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
3 | O | O | O | O | O | O | O | O |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
4 | O | O | X | O | O | O | O | O |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
5 | O | O | O | X | O | X | O | X |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
6 | O | X | O | X | X | O | O | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
7 | O | X | X | O | O | O | O | O |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
8 | O | X | X | O | | | X | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
You have 12 points. The computer has 48 points.
Enter your move, or type quit to end the game, or hints to turn
off/on hints.
86
X scored 15 points. O scored 46 points.
You lost. The computer beat you by 31 points.
Do you want to play again? (yes or no)
no
As you can see, the AI was pretty good at beating me. To help the player out, we'll program our game to provide hints. If the player types 'hints' as their move, they can toggle the hints mode on and off. When hints mode is on, all the possible moves the player can make will show up on the board as '.' characters, like this:
1 2 3 4 5 6 7 8
+---+---+---+---+---+---+---+---+
| | | | | | | | |
1 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
2 | | | | . | | . | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
3 | | | | O | O | O | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
4 | | | . | O | O | X | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
5 | | | . | O | O | O | X | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
6 | | | | . | | . | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
7 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
8 | | | | | | | | |
| | | | | | | | |
+---+---+---+---+---+---+---+---+