# 11.6: Source Code for Four-In-A-Row

$$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$

$$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$

$$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$

( \newcommand{\kernel}{\mathrm{null}\,}\) $$\newcommand{\range}{\mathrm{range}\,}$$

$$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$

$$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$

$$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$

$$\newcommand{\Span}{\mathrm{span}}$$

$$\newcommand{\id}{\mathrm{id}}$$

$$\newcommand{\Span}{\mathrm{span}}$$

$$\newcommand{\kernel}{\mathrm{null}\,}$$

$$\newcommand{\range}{\mathrm{range}\,}$$

$$\newcommand{\RealPart}{\mathrm{Re}}$$

$$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$

$$\newcommand{\Argument}{\mathrm{Arg}}$$

$$\newcommand{\norm}[1]{\| #1 \|}$$

$$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$

$$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\AA}{\unicode[.8,0]{x212B}}$$

$$\newcommand{\vectorA}[1]{\vec{#1}} % arrow$$

$$\newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow$$

$$\newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$

$$\newcommand{\vectorC}[1]{\textbf{#1}}$$

$$\newcommand{\vectorD}[1]{\overrightarrow{#1}}$$

$$\newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}}$$

$$\newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}}$$

$$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$

$$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$

$$\newcommand{\avec}{\mathbf a}$$ $$\newcommand{\bvec}{\mathbf b}$$ $$\newcommand{\cvec}{\mathbf c}$$ $$\newcommand{\dvec}{\mathbf d}$$ $$\newcommand{\dtil}{\widetilde{\mathbf d}}$$ $$\newcommand{\evec}{\mathbf e}$$ $$\newcommand{\fvec}{\mathbf f}$$ $$\newcommand{\nvec}{\mathbf n}$$ $$\newcommand{\pvec}{\mathbf p}$$ $$\newcommand{\qvec}{\mathbf q}$$ $$\newcommand{\svec}{\mathbf s}$$ $$\newcommand{\tvec}{\mathbf t}$$ $$\newcommand{\uvec}{\mathbf u}$$ $$\newcommand{\vvec}{\mathbf v}$$ $$\newcommand{\wvec}{\mathbf w}$$ $$\newcommand{\xvec}{\mathbf x}$$ $$\newcommand{\yvec}{\mathbf y}$$ $$\newcommand{\zvec}{\mathbf z}$$ $$\newcommand{\rvec}{\mathbf r}$$ $$\newcommand{\mvec}{\mathbf m}$$ $$\newcommand{\zerovec}{\mathbf 0}$$ $$\newcommand{\onevec}{\mathbf 1}$$ $$\newcommand{\real}{\mathbb R}$$ $$\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}$$ $$\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}$$ $$\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}$$ $$\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}$$ $$\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}$$ $$\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}$$ $$\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}$$ $$\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}$$ $$\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}$$ $$\newcommand{\laspan}[1]{\text{Span}\{#1\}}$$ $$\newcommand{\bcal}{\cal B}$$ $$\newcommand{\ccal}{\cal C}$$ $$\newcommand{\scal}{\cal S}$$ $$\newcommand{\wcal}{\cal W}$$ $$\newcommand{\ecal}{\cal E}$$ $$\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}$$ $$\newcommand{\gray}[1]{\color{gray}{#1}}$$ $$\newcommand{\lgray}[1]{\color{lightgray}{#1}}$$ $$\newcommand{\rank}{\operatorname{rank}}$$ $$\newcommand{\row}{\text{Row}}$$ $$\newcommand{\col}{\text{Col}}$$ $$\renewcommand{\row}{\text{Row}}$$ $$\newcommand{\nul}{\text{Nul}}$$ $$\newcommand{\var}{\text{Var}}$$ $$\newcommand{\corr}{\text{corr}}$$ $$\newcommand{\len}[1]{\left|#1\right|}$$ $$\newcommand{\bbar}{\overline{\bvec}}$$ $$\newcommand{\bhat}{\widehat{\bvec}}$$ $$\newcommand{\bperp}{\bvec^\perp}$$ $$\newcommand{\xhat}{\widehat{\xvec}}$$ $$\newcommand{\vhat}{\widehat{\vvec}}$$ $$\newcommand{\uhat}{\widehat{\uvec}}$$ $$\newcommand{\what}{\widehat{\wvec}}$$ $$\newcommand{\Sighat}{\widehat{\Sigma}}$$ $$\newcommand{\lt}{<}$$ $$\newcommand{\gt}{>}$$ $$\newcommand{\amp}{&}$$ $$\definecolor{fillinmathshade}{gray}{0.9}$$

# Four-In-A-Row (a Connect Four clone)
# By Al Sweigart al@inventwithpython.com
# http://inventwithpython.com/pygame
# Released under a "Simplified BSD" license

import random, copy, sys, pygame
from pygame.locals import *

BOARDWIDTH = 7  # how many spaces wide the board is
BOARDHEIGHT = 6 # how many spaces tall the board is
assert BOARDWIDTH >= 4 and BOARDHEIGHT >= 4, 'Board must be at least 4x4.'

DIFFICULTY = 2 # how many moves to look ahead. (>2 is usually too much)

SPACESIZE = 50 # size of the tokens and individual board spaces in pixels

FPS = 30 # frames per second to update the screen
WINDOWWIDTH = 640 # width of the program's window, in pixels
WINDOWHEIGHT = 480 # height in pixels

XMARGIN = int((WINDOWWIDTH - BOARDWIDTH * SPACESIZE) / 2)
YMARGIN = int((WINDOWHEIGHT - BOARDHEIGHT * SPACESIZE) / 2)

BRIGHTBLUE = (0, 50, 255)
WHITE = (255, 255, 255)

BGCOLOR = BRIGHTBLUE
TEXTCOLOR = WHITE

RED = 'red'
BLACK = 'black'
EMPTY = None
HUMAN = 'human'
COMPUTER = 'computer'

def main():
global FPSCLOCK, DISPLAYSURF, REDPILERECT, BLACKPILERECT, REDTOKENIMG
global BLACKTOKENIMG, BOARDIMG, ARROWIMG, ARROWRECT, HUMANWINNERIMG
global COMPUTERWINNERIMG, WINNERRECT, TIEWINNERIMG

pygame.init()
FPSCLOCK = pygame.time.Clock()
DISPLAYSURF = pygame.display.set_mode((WINDOWWIDTH, WINDOWHEIGHT))
pygame.display.set_caption('Four in a Row')

REDPILERECT = pygame.Rect(int(SPACESIZE / 2), WINDOWHEIGHT - int(3 * SPACESIZE / 2), SPACESIZE, SPACESIZE)
BLACKPILERECT = pygame.Rect(WINDOWWIDTH - int(3 * SPACESIZE / 2), WINDOWHEIGHT - int(3 * SPACESIZE / 2), SPACESIZE, SPACESIZE)
REDTOKENIMG = pygame.transform.smoothscale(REDTOKENIMG, (SPACESIZE, SPACESIZE))
BLACKTOKENIMG = pygame.transform.smoothscale(BLACKTOKENIMG, (SPACESIZE, SPACESIZE))
BOARDIMG = pygame.transform.smoothscale(BOARDIMG, (SPACESIZE, SPACESIZE))

WINNERRECT = HUMANWINNERIMG.get_rect()
WINNERRECT.center = (int(WINDOWWIDTH / 2), int(WINDOWHEIGHT / 2))

ARROWRECT = ARROWIMG.get_rect()
ARROWRECT.left = REDPILERECT.right + 10
ARROWRECT.centery = REDPILERECT.centery

isFirstGame = True

while True:
runGame(isFirstGame)
isFirstGame = False

def runGame(isFirstGame):
if isFirstGame:
# Let the computer go first on the first game, so the player
# can see how the tokens are dragged from the token piles.
turn = COMPUTER
showHelp = True
else:
# Randomly choose who goes first.
if random.randint(0, 1) == 0:
turn = COMPUTER
else:
turn = HUMAN
showHelp = False

# Set up a blank board data structure.
mainBoard = getNewBoard()

while True: # main game loop
if turn == HUMAN:
# Human player's turn.
getHumanMove(mainBoard, showHelp)
if showHelp:
# turn off help arrow after the first move
showHelp = False
if isWinner(mainBoard, RED):
winnerImg = HUMANWINNERIMG
break
turn = COMPUTER # switch to other player's turn
else:
# Computer player's turn.
column = getComputerMove(mainBoard)
animateComputerMoving(mainBoard, column)
makeMove(mainBoard, BLACK, column)
if isWinner(mainBoard, BLACK):
winnerImg = COMPUTERWINNERIMG
break
turn = HUMAN # switch to other player's turn

if isBoardFull(mainBoard):
# A completely filled board means it's a tie.
winnerImg = TIEWINNERIMG
break

while True:
# Keep looping until player clicks the mouse or quits.
drawBoard(mainBoard)
DISPLAYSURF.blit(winnerImg, WINNERRECT)
pygame.display.update()
FPSCLOCK.tick()
for event in pygame.event.get(): # event handling loop
if event.type == QUIT or (event.type == KEYUP and event.key == K_ESCAPE):
pygame.quit()
sys.exit()
elif event.type == MOUSEBUTTONUP:
return

def makeMove(board, player, column):
lowest = getLowestEmptySpace(board, column)
if lowest != -1:
board[column][lowest] = player

def drawBoard(board, extraToken=None):
DISPLAYSURF.fill(BGCOLOR)

# draw tokens
spaceRect = pygame.Rect(0, 0, SPACESIZE, SPACESIZE)
for x in range(BOARDWIDTH):
for y in range(BOARDHEIGHT):
spaceRect.topleft = (XMARGIN + (x * SPACESIZE), YMARGIN + (y * SPACESIZE))
if board[x][y] == RED:
DISPLAYSURF.blit(REDTOKENIMG, spaceRect)
elif board[x][y] == BLACK:
DISPLAYSURF.blit(BLACKTOKENIMG, spaceRect)

# draw the extra token
if extraToken != None:
if extraToken['color'] == RED:
DISPLAYSURF.blit(REDTOKENIMG, (extraToken['x'], extraToken['y'], SPACESIZE, SPACESIZE))
elif extraToken['color'] == BLACK:
DISPLAYSURF.blit(BLACKTOKENIMG, (extraToken['x'], extraToken['y'], SPACESIZE, SPACESIZE))

# draw board over the tokens
for x in range(BOARDWIDTH):
for y in range(BOARDHEIGHT):
spaceRect.topleft = (XMARGIN + (x * SPACESIZE), YMARGIN + (y * SPACESIZE))
DISPLAYSURF.blit(BOARDIMG, spaceRect)

# draw the red and black tokens off to the side
DISPLAYSURF.blit(REDTOKENIMG, REDPILERECT) # red on the left
DISPLAYSURF.blit(BLACKTOKENIMG, BLACKPILERECT) # black on the right

def getNewBoard():
board = []
for x in range(BOARDWIDTH):
board.append([EMPTY] * BOARDHEIGHT)
return board

def getHumanMove(board, isFirstMove):
draggingToken = False
tokenx, tokeny = None, None
while True:
for event in pygame.event.get(): # event handling loop
if event.type == QUIT:
pygame.quit()
sys.exit()
elif event.type == MOUSEBUTTONDOWN and not draggingToken and REDPILERECT.collidepoint(event.pos):
# start of dragging on red token pile.
draggingToken = True
tokenx, tokeny = event.pos
elif event.type == MOUSEMOTION and draggingToken:
# update the position of the red token being dragged
tokenx, tokeny = event.pos
elif event.type == MOUSEBUTTONUP and draggingToken:
# let go of the token being dragged
if tokeny < YMARGIN and tokenx > XMARGIN and tokenx < WINDOWWIDTH - XMARGIN:
# let go at the top of the screen.
column = int((tokenx - XMARGIN) / SPACESIZE)
if isValidMove(board, column):
animateDroppingToken(board, column, RED)
board[column][getLowestEmptySpace(board, column)] = RED
drawBoard(board)
pygame.display.update()
return
tokenx, tokeny = None, None
draggingToken = False
if tokenx != None and tokeny != None:
drawBoard(board, {'x':tokenx - int(SPACESIZE / 2), 'y':tokeny - int(SPACESIZE / 2), 'color':RED})
else:
drawBoard(board)

if isFirstMove:
# Show the help arrow for the player's first move.
DISPLAYSURF.blit(ARROWIMG, ARROWRECT)

pygame.display.update()
FPSCLOCK.tick()

def animateDroppingToken(board, column, color):
x = XMARGIN + column * SPACESIZE
y = YMARGIN - SPACESIZE
dropSpeed = 1.0

lowestEmptySpace = getLowestEmptySpace(board, column)

while True:
y += int(dropSpeed)
dropSpeed += 0.5
if int((y - YMARGIN) / SPACESIZE) >= lowestEmptySpace:
return
drawBoard(board, {'x':x, 'y':y, 'color':color})
pygame.display.update()
FPSCLOCK.tick()

def animateComputerMoving(board, column):
x = BLACKPILERECT.left
y = BLACKPILERECT.top
speed = 1.0
# moving the black tile up
while y > (YMARGIN - SPACESIZE):
y -= int(speed)
speed += 0.5
drawBoard(board, {'x':x, 'y':y, 'color':BLACK})
pygame.display.update()
FPSCLOCK.tick()
# moving the black tile over
y = YMARGIN - SPACESIZE
speed = 1.0
while x > (XMARGIN + column * SPACESIZE):
x -= int(speed)
speed += 0.5
drawBoard(board, {'x':x, 'y':y, 'color':BLACK})
pygame.display.update()
FPSCLOCK.tick()
# dropping the black tile
animateDroppingToken(board, column, BLACK)

def getComputerMove(board):
potentialMoves = getPotentialMoves(board, BLACK, DIFFICULTY)
bestMoveFitness = -1
for i in range(BOARDWIDTH):
if potentialMoves[i] > bestMoveFitness and isValidMove(board, i):
bestMoveFitness = potentialMoves[i]
# find all potential moves that have this best fitness
bestMoves = []
for i in range(len(potentialMoves)):
if potentialMoves[i] == bestMoveFitness and isValidMove(board, i):
bestMoves.append(i)
return random.choice(bestMoves)

if lookAhead == 0 or isBoardFull(board):
return [0] * BOARDWIDTH

if tile == RED:
enemyTile = BLACK
else:
enemyTile = RED

# Figure out the best move to make.
potentialMoves = [0] * BOARDWIDTH
for firstMove in range(BOARDWIDTH):
dupeBoard = copy.deepcopy(board)
if not isValidMove(dupeBoard, firstMove):
continue
makeMove(dupeBoard, tile, firstMove)
if isWinner(dupeBoard, tile):
# a winning move automatically gets a perfect fitness
potentialMoves[firstMove] = 1
break # don't bother calculating other moves
else:
# do other player's counter moves and determine best one
if isBoardFull(dupeBoard):
potentialMoves[firstMove] = 0
else:
for counterMove in range(BOARDWIDTH):
dupeBoard2 = copy.deepcopy(dupeBoard)
if not isValidMove(dupeBoard2, counterMove):
continue
makeMove(dupeBoard2, enemyTile, counterMove)
if isWinner(dupeBoard2, enemyTile):
# a losing move automatically gets the worst fitness
potentialMoves[firstMove] = -1
break
else:
# do the recursive call to getPotentialMoves()
results = getPotentialMoves(dupeBoard2, tile, lookAhead - 1)
potentialMoves[firstMove] += (sum(results) / BOARDWIDTH) / BOARDWIDTH
return potentialMoves

def getLowestEmptySpace(board, column):
# Return the row number of the lowest empty row in the given column.
for y in range(BOARDHEIGHT-1, -1, -1):
if board[column][y] == EMPTY:
return y
return -1

def isValidMove(board, column):
# Returns True if there is an empty space in the given column.
# Otherwise returns False.
if column < 0 or column >= (BOARDWIDTH) or board[column][0] != EMPTY:
return False
return True

def isBoardFull(board):
# Returns True if there are no empty spaces anywhere on the board.
for x in range(BOARDWIDTH):
for y in range(BOARDHEIGHT):
if board[x][y] == EMPTY:
return False
return True

def isWinner(board, tile):
# check horizontal spaces
for x in range(BOARDWIDTH - 3):
for y in range(BOARDHEIGHT):
if board[x][y] == tile and board[x+1][y] == tile and board[x+2][y] == tile and board[x+3][y] == tile:
return True
# check vertical spaces
for x in range(BOARDWIDTH):
for y in range(BOARDHEIGHT - 3):
if board[x][y] == tile and board[x][y+1] == tile and board[x][y+2] == tile and board[x][y+3] == tile:
return True
# check / diagonal spaces
for x in range(BOARDWIDTH - 3):
for y in range(3, BOARDHEIGHT):
if board[x][y] == tile and board[x+1][y-1] == tile and board[x+2][y-2] == tile and board[x+3][y-3] == tile:
return True
# check \ diagonal spaces
for x in range(BOARDWIDTH - 3):
for y in range(BOARDHEIGHT - 3):
if board[x][y] == tile and board[x+1][y+1] == tile and board[x+2][y+2] == tile and board[x+3][y+3] == tile:
return True
return False

if __name__ == '__main__':
main()


This page titled 11.6: Source Code for Four-In-A-Row is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Al Sweigart via source content that was edited to the style and standards of the LibreTexts platform.