12.2. CASESTUDY: RACQUETBALLSIMULATION 207

12.2.4 ImplementingPlayer

IndevelopingtheRBallGameclass,wediscoveredtheneedforaPlayerclassthatencapsulatesthe
serviceprobabilityandcurrentscorefora player. ThePlayerclassneedsa suitableconstructorandmethods
forwinsServe,incScoreandgetScore.
If youaregettingthehangofthisobject-orientedapproach,youshouldhave notroublecomingupwith
a constructor. We justneedtoinitializetheinstancevariables.Theplayer’s probabilitywillbepassedasa
parameter, andthescorestartsat 0.

def __init__(self,prob):

# Create a playerwith this probability

self.prob = prob

self.score= 0

TheothermethodsforourPlayerclassareevensimpler. To seeif a playerwinsa serve, wecompare
theprobabilitytoa randomnumberbetween0 and1.

def winsServe(self):

return random()<= self.prob

To give a playera point,wesimplyaddonetothescore.

def incScore(self):

self.score= self.score + 1

Thefinalmethodjustreturnsthevalueofthescore.

def getScore(self):

return self.score

Initially, youmaythinkthatit’s sillytocreatea classwitha bunchofone-ortwo-linemethods.Actually,
it’s quitecommonfora well-modularized,objected-orientedprogramtohave lotsoftrivialmethods. The
pointofdesignistobreaka problemdownintosimplerpieces. Ifthosepiecesaresosimplethattheir
implementationis obvious,thatgivesusconfidencethatwemusthave gottenit right.

12.2.5 TheCompleteProgram.

Thatprettymuchwrapsupourobject-orientedversionoftheracquetballsimulation.Thecompleteprogram
follows.Youshouldreadthroughit andmake sureyouunderstandexactlywhateachclassdoesandhow it
doesit.If youhave questionsaboutany parts,gobacktothediscussionabove tofigureit out.

objrball.py -- Simulationof a racquet game.

Illustratesdesign with objects.

from random importrandom

class Player:

A Player keepstrack of service probability and score

def __init__(self,prob):

# Create a playerwith this probability

self.prob = prob

self.score= 0

def winsServe(self):

# RETURNS a Booleanthat is true with probability self.prob

return random()<= self.prob