Homework 6, Problem 2: Connect Four: The Board class
[60 points;
individual or pair]
Submission: Submit your hw6pr2.py file to Canvas
Connect Four is a variation of tic-tac-toe played on a 7x6 rectangular
board: 
The game is played by two players, alternating turns, with each trying
to place four checkers in a row vertically, horizontally, or diagonally. One
constraint in the game is that because the board stands vertically, the
checkers cannot be placed into an arbitrary position. A checker may only be
placed at the top of one of the currently existing columns (or it may start a
new column).
The Board class -- a
preview
In this problem, you will need to create a class named Board that implements some of the features of the Connect Four
game. The Board class will have three data members: there
will be a two-dimensonal list (a list of lists) containing characters to
represent the game area, and a pair of variables holding the number of rows and
columns on the board (6 rows and 7 columns is standard), but your Board datatype will be able to handle boards of any size.
Even as we allow arbitrary board sizes, however, we will preserve the
four-in-a-row requirement for winning the game. Admittedly, this makes it hard
to win the game on a 3x3 board.
Your task is to write the Board class. Details appear here:
Your Board class should have at least three data
members:
- A variable data storing the two-dimensional
array (list of lists), which is the game board
- A variable height storing the number of rows on
the game board
- A variable width storing the number of columns
on the game board
Note that the two-dimensional list is a two-dimensional list of characters,
which are just strings of length 1. You should represent an empty slot by ' ', which is the space character -- not the empty string. You
should represent player X's checkers with an 'X' (the capital x character) and you should
represent player O's checkers with an 'O' (the capital o character).
Warning!
A very difficult bug to find occurs if you use the zero '0' character instead of the 'O' character
(capital-O) to represent one of the players. The problem occurs when you or the
graders start comparing values in the board with the wrong one! Be sure to stay
consistent with the capital-O character.
Methods required for the Board class :
You should provide your Board class with write the following methods.
Be sure to try the hints on how to test each one after writing it! The first
two methods were written in class and are provided for copy-and-paste, below.
However, they were written with magic numbers of 7 columns and 6
rows. You will need to change the code below so that arbitrarily-sized boards
are available.
__init__, the constructor
- __init__(self, width, height):
This is a constructor for Board objects that takes two arguments. (Remember that self refers to the object being constructed and that it is not explicitly passed into the constructor.) This constructor takes in a number of columns and rows (7 and 6 are the connect-four standard, but our datatype will handle arbitrarily-sized boards). The constructor will set the values of the data members of the object. In addition, it will initialize the two-dimensional list representing the board. You will want to construct a list of lists very much in the spirit of the game-of-life lab.
Note that you don't want self.data to contain all of the characters that go into printing the board -- only the ones that affect the play of the game. The extra characters will be generated in the __repr__ method.
__repr__, for printing or any string representation
- __repr__(self):
This method returns a string representing the Board object that calls it. Basically, each "checker" takes up one space, and all columns are separated by vertical bars (|). The columns are labeled at the bottom. Here is an example for a 6-row and 7-column (6x7) board (see the code below for details...)
| | | | | | | |
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| | | | | | | |
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| | | | | | | |
| | | | | | | |
---------------
0 1 2 3 4 5 6
In order to keep things in line, the column-numbering should be done "mod 10," as this larger 5-row, 15-column (5x15) example shows:
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
-------------------------------
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
One string, multiple lines?
The string
'\n'
represents the newline character in Python. Thus, you can get
multiple lines into a single string by adding '\n'. For example,
>>> s = 'This is the top line.'
>>> s += '\n'
>>> s += 'This is a second line!\n'
>>> print(s)
This is the top line.
This is a second line!
>>>
Notice
that the '\n' can be included within a string,
as well. In this case, it added an extra blank line at the end of s.
The code to start with...
Here is the code to start with -- remember that you will need to get rid
of the magic numbers (7 columns and 6 rows) as you generalize this code
to have width columns and height rows.
class Board:
""" a datatype representing a
C4 board
with an arbitrary number of rows and cols
"""
def __init__( self, width, height ):
""" the
constructor for objects of type Board """
self.width = width
self.height = height
self.data = [] # this will be the board
for row in range( 6 ):
boardRow = []
for col in range( 7 ):
boardRow += [' '] # add a space to this row
self.data += [boardRow] #
add this row to the board
# do not need to return
inside a constructor!
def __repr__(self):
""" this
method returns a string representation
for an object of type Board
"""
s = '' # the string to return
for row in range( 6 ):
s += '|' # add the spacer character
for col in range( 7 ):
s += self.data[row][col] +
'|'
s += '\n'
# add the bottom of the
board
# and the numbers underneath
here
return s # the board is complete, return it
Next,
implement the following methods in your Board class. Be sure to test each one after you
write it -- it's much easier to make sure each works one-at-a-time than trying
to debug a huge collection of methods all at once.
addMove, for dropping a checker into the board
- addMove(self, col, ox):
This method takes two inputs: the first input col represents the index of the column to which the checker will be added; the second input ox will be a 1-character string representing the checker to add to the board. That is, ox should either be 'X' or 'O' (again, capital O, not zero).
Remember that the checker slides down from the top of the
board! Thus, your code will have to find the appropriate row number
available in column col and put the checker in that row. In addMove you do not have to check that col is a legal column number or that there is space in column col. That checking is
important, however. The next method, which is called allowsMove, will do just that.
Testing addMove
Here is a sequence for testing addMove --
try it out!
>>> b = Board(7,6)
>>> b.addMove(0, 'X')
>>> b.addMove(0, 'O')
>>> b.addMove(0, 'X')
>>> b.addMove(3, 'O')
>>> b.addMove(4, 'O') #
cheating by letting O go again!
>>> b.addMove(5, 'O')
>>> b.addMove(6, 'O')
>>> b
| | | | | | | |
| | | | | | | |
| | | | | | | |
|X| | | | | | |
|O| | | | | | |
|X| | |O|O|O|O|
---------------
0 1 2 3 4 5 6
clear, should clear the board that calls it.
Not much to say about clear( self ). It's useful,
though!
setBoard, for checking if a column is a legal
move
This one is really useful for quickly creating a board to test your
lookahead in the next problem. Here is the code we used for
setBoard:
def setBoard( self, moveString ):
""" takes in
a string of columns and places
alternating checkers in
those columns,
starting with 'X'
For example, call
b.setBoard('012345')
to see 'X's and 'O's
alternate on the
bottom row, or
b.setBoard('000000') to
see them alternate in the
left column.
moveString must be a string
of integers
"""
nextCh = 'X'
for colString in moveString:
col = int(colString)
if 0 <= col <=
self.width:
self.addMove(col, nextCh)
if nextCh == 'X': nextCh =
'O'
else: nextCh = 'X'
allowsMove, for checking if a column is a
legal move
- allowsMove(self, c):
This method should return True if the calling object (of type Board) does allow a move into column c. It returns False if column c is not a legal column number for the calling object. It also returns False if column c is full. Thus, this method should check to be sure that c is within the range from 0 to the last column and make sure that there is still room left in the column!
Testing allowsMove
Here is an example sequence for testing -- try it!
>>> b = Board(2,2)
>>> b
| | |
| | |
-----
0 1
>>> b.addMove(0, 'X')
>>> b.addMove(0, 'O')
>>> b
|O| |
|X| |
-----
0 1
>>> b.allowsMove(-1)
False
>>> b.allowsMove(0)
False
>>> b.allowsMove(1)
True
>>> b.allowsMove(2)
False
isFull, checks if the board is full
- isFull(self):
This method should return True if the calling object (of type Board) is completely full of checkers. It should return False otherwise. Notice that you can leverage allowsMove to make this method very concise! Unless you're supernaturally patient, you'll want to test this on small boards:
Testing isFull
Here is an example sequence for testing (it uses setBoard, above)
>>> b = Board(2,2)
>>> b.isFull()
False
>>> b.setBoard( '0011' )
>>> b
|O|O|
|X|X|
-----
0 1
>>> b.isFull()
True
delMove, removes a checker from the board
- delMove(self, c):
This method should do the opposite of addMove. It should remove the top checker from the column c. If the column is empty, then delMove should do nothing. This function may not seem useful now, but it will become very useful when you try to implement your own Connect Four player.
Testing delMove
Here is an example sequence for testing:
>>> b = Board(2,2)
>>> b.setBoard( '0011' )
>>> b.delMove(1)
>>> b.delMove(1)
>>> b.delMove(1)
>>> b.delMove(0)
>>> b
| | |
|X| |
-----
0 1
winsFor, checks if someone has won the game
- winsFor(self, ox): This
method's input ox is a 1-character checker: either 'X' or 'O'. It should
return True if there are four checkers of
type ox in a row on the board. It
should return False othwerwise. Important
Note: you need to check if the player has won horizontally,
vertically, or diagonally (and there are two different directions for a
diagonal win).
One way to approach this is to consider each possible anchor checker that might start a four-in-a-row run. for example, all of the "anchors" that might start a horizontal run (going from left to right) must be in the columns at least four places from the end of the board. That constraint will help you avoid out-of-bounds errors. Here is some starter code that illustrates this technique (but as of yet only checks for horizontal wins):
# check for horizontal wins
for row in range(0,self.height):
for col in range(0,self.width-3):
if self.data[row][col] == ox
and \
self.data[row][col+1] == ox
and \
self.data[row][col+2] == ox
and \
self.data[row][col+3] == ox:
return True
Note the backslash characters -- these tell Python that the line of
code will continue on the next line of the file. Note, too, the -3 that keeps the checking in bounds. Different directions
will require different guards against going out of bounds.
Warning I would advise against explicitly counting
checkers to see if you reach four. The problem is that you must visit each
checker in the right order. Vertical and horizontal orderings aren't bad, but
visiting each checker in diagonal order is neither easy nor informative. It's
more convenient to check for all four checkers at once, as in the previous
example.
This is an important method to test thoroughly! The following is only
one test:
Testing winsFor
Here is an example sequence for testing:
>>> b = Board(7,6)
>>> b.setBoard( '00102030' )
>>> b.winsFor('X')
True
>>> b.winsFor('O')
True
>>> b = Board(7,6)
>>> b.setBoard( '00102030' )
>>> b.winsFor('X')
True
>>> b.winsFor('O')
True
>>> b = Board(7,6)
>>> b.setBoard( '23344545515' )
>>> b
| | | | | | | |
| | | | | | | |
| | | | | |X| |
| | | | |X|X| |
| | | |X|X|O| |
| |O|X|O|O|O| |
---------------
0 1 2 3 4 5 6
>>> b.winsFor('X') #
diagonal
True
>>> b.winsFor('O')
False
hostGame, hosts a full game of Connect Four
- hostGame(self): This method brings everything
together into the familiar game. It should host a game of connect four,
using the methods listed above to do so. In particular, it should
alternate turns between 'X' (who will always go first) and 'O' (who will always go second).
It should ask the user (with the input function) to
select a column number for each move. See below for an example of how the
interaction should work, but here are a few important points to keep in
mind:
This method should print the board before prompting for each move.
After each input, you should
check if the column chosen is a valid one. Thus, this method should detect
illegal moves, either out-of-bounds or a full column, and prompt for another
move instead. You do not have to check if the input is an integer, however; you
may assume it will always be one. This method should place the checker into its
(valid) column. Then, it should check if that player has won the game or if the
board is now full.
If the game is over for either reason, the game should stop, the board
should be printed out one last time, and the program should report who won (or
that it was a tie.)
If the game is not over, the other player should be prompted to make a
move, and so on.
Be sure to test this method by playing the game a few times (with each
possible ending)!
Here is an example run, to give a sense of the input and output:
>>> b = Board(7,6)
>>> b.hostGame()
Welcome to Connect Four!
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---------------
0 1 2 3 4 5 6
X's choice: 3
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| | | | | | | |
| | | | | | | |
| | | |X| | | |
---------------
0 1 2 3 4 5 6
O's choice: 4
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | |X|O| | |
---------------
0 1 2 3 4 5 6
X's choice: 2
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | |X|X|O| | |
---------------
0 1 2 3 4 5 6
O's choice: 4
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | |O| | |
| | |X|X|O| | |
---------------
0 1 2 3 4 5 6
X's choice: 1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | |O| | |
| |X|X|X|O| | |
---------------
0 1 2 3 4 5 6
O's choice: 2
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | |O| |O| | |
| |X|X|X|O| | |
---------------
0 1 2 3 4 5 6
X's choice: 0
X wins -- Congratulations!
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | |O| |O| | |
|X|X|X|X|O| | |
---------------
0 1 2 3 4 5 6
>>>
If you have gotten to this point, you have completed problem 2! You
should submit your hw6pr2.py file at Canvas .
The next (extra!) problem will ask you to make a copy of this file and
extend it to build an "AI" player for the game of connect four!
Next