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Introductionto Computingand Programming inPython TM

AMULTIMEDIA APPROACH

MarkJ.GuzdialandBarbaraEricson

CollegeofComputing/GVU

GeorgiaInstituteofTechnology

FourthEdition

GlobalEdition

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AuthorizedadaptationfromtheUnitedStatesedition,entitledIntroductiontoComputingandProgramminginPython™ :AMultimediaApproach,Fourth Edition,ISBN9780134025544,byMarkJ.GuzdialandBarbaraEricsonpublishedbyPearsonEducation © 2016.

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Dedicatedtoourﬁrstteachers,ourparents: Janet,Charles,Gene,andNancy

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PrefacefortheFourthEdition13

PrefacetotheFirstEdition18

AbouttheAuthors24

1 INTRODUCTION 25

1 IntroductiontoComputerScienceandMedia Computation 27

1.1WhatIsComputerScienceAbout?27

1.2ProgrammingLanguages30

1.3WhatComputersUnderstand33

1.4MediaComputation:WhyDigitizeMedia?35

1.5ComputerScienceforEveryone37

1.5.1It’sAboutCommunication37

1.5.2It’sAboutProcess37

1.5.3YouWillProbablyNeedIt38

2 IntroductiontoProgramming 42

2.1ProgrammingIsAboutNaming42

2.1.1FilesandTheirNames44

2.2ProgramminginPython45

2.3ProgramminginJES46

2.4MediaComputationinJES47

2.4.1ShowingaPicture51

2.4.2PlayingaSound54

2.4.3NamingValues54

2.5MakingaProgram57

2.5.1Functions:RealMath-LikeFunctionsThatTake Input61

3 CreatingandModifyingText 68

3.1Strings:MakingHumanTextinaComputer68

3.1.1MakingStringsfromStrings:TellingStories70

3.2TakingStringsApartwith For 73

3.2.1TestingthePieces75

3.2.2TakingStringApart,andPuttingStringsTogether78

3.2.3TakingStringsApartwithIndices81

3.2.4Mirroring,Reversing,andSeparatingStringswithIndex83

3.2.5EncodingandDecodingStringsUsingaKeywordCipher85

3.3TakingStringsApartbyWords87

3.4What’sInsideaString90

3.5WhataComputerCanDo91

4 ModifyingPicturesUsingLoops 98

4.1HowPicturesAreEncoded99

4.2ManipulatingPictures104

4.2.1ExploringPictures108

4.3ChangingColorValues110

4.3.1UsingLoopsinPictures110

4.3.2Increasing/DecreasingRed(Green,Blue)112

4.3.3TestingtheProgram:DidThatReallyWork?117

4.3.4ChangingOneColorataTime118

4.4CreatingaSunset119

4.4.1MakingSenseofFunctions119

4.5LighteningandDarkening124

4.6CreatingaNegative125

4.7ConvertingtoGrayscale126

4.8SpecifyingPixelsbyIndex128

5 PictureTechniqueswithSelection 138

5.1ReplacingColors:Red-Eye,SepiaTones,andPosterizing138

5.1.1ReducingRed-Eye142

5.1.2Sepia-TonedandPosterizedPictures:Using ConditionalstoChoosetheColor144

5.2ComparingPixels:EdgeDetection150

5.3BackgroundSubtraction153

5.4Chromakey156

5.5Coloringinranges161

5.5.1AddingaBorder161

5.5.2LighteningtheRightHalfofaPicture162

5.6SelectingwithoutRetesting163

6 ModifyingPixelsbyPosition 169

6.1ProcessingPixelsFaster169

6.1.1LoopingacrossthePixelswith Range 171

6.1.2WritingFasterPixelLoops173

6.2MirroringaPicture175

6.3CopyingandTransformingPictures182

6.3.1Copying183

6.3.2CopyingSmallerandModifying189

6.3.3CopyingandReferencing191

6.3.4CreatingaCollage193

6.3.5GeneralCopying196

6.3.6Rotation197

6.3.7Scaling200

6.4CombiningPixels:Blurring205

6.5BlendingPictures208

6.6DrawingonImages210

6.6.1DrawingwithDrawingCommands212

6.6.2VectorandBitmapRepresentations213

6.7ProgramsasSpecifyingDrawingProcess215

6.7.1WhyDoWeWritePrograms?216

2 SOUND 225

7 ModifyingSoundsUsingLoops 227

7.1HowSoundIsEncoded227

7.1.1ThePhysicsofSound227

7.1.2InvestigatingDifferentSounds230

7.1.3EncodingtheSound235

7.1.4BinaryNumbersandTwo’sComplement236

7.1.5StoringDigitizedSounds237

7.2ManipulatingSounds239

7.2.1OpenSoundsandManipulatingSamples239

7.2.2UsingtheJESMediaTools242

7.2.3Looping243

7.3ChangingtheVolumeofSounds244

7.3.1IncreasingVolume244

7.3.2DidThatReallyWork?245

7.3.3DecreasingVolume249

7.3.4UsingArrayIndexNotation250

7.3.5MakingSenseofFunctionsinSounds251

7.4NormalizingSounds251

7.4.1GeneratingClipping253

8 ModifyingSamplesinaRange 259

8.1ManipulatingDifferentSectionsoftheSoundDifferently259

8.1.1RevisitingIndexArrayNotation260

8.2SplicingSounds262

8.3GeneralClipandCopy269

8.4ReversingSounds271

8.5Mirroring273

8.6OnFunctionsandScope273

9 MakingSoundsbyCombiningPieces 279

9.1ComposingSoundsThroughAddition279

9.2BlendingSounds280

9.3CreatinganEcho282

9.3.1CreatingMultipleEchoes284

9.3.2CreatingChords284

9.4HowSamplingKeyboardsWork285

9.4.1SamplingasanAlgorithm289

9.5AdditiveSynthesis289

9.5.1MakingSineWaves289

9.5.2AddingSineWavesTogether291

9.5.3CheckingOurResult292

9.5.4SquareWaves293

9.5.5TriangularWaves295

9.6ModernMusicSynthesis297

9.6.1MP3297

9.6.2MIDI298

10 BuildingBiggerPrograms 302

10.1DesigningProgramsTop-Down303

10.1.1ATop-DownDesignExample304

10.1.2DesigningtheTop-LevelFunction305

10.1.3WritingtheSubfunctions307

10.2DesigningProgramsBottom-Up311

10.2.1AnExampleBottom-UpProcess312

10.3TestingYourProgram312

10.3.1TestingtheEdgeConditions314

10.4TipsonDebugging315

10.4.1FindingWhichStatementtoWorryAbout316

10.4.2SeeingtheVariables316

10.4.3DebuggingtheAdventureGame318

10.5AlgorithmsandDesign321

10.6ConnectingtoDataOutsideaFunction322

10.7RunningProgramsOutsideofJES326

3 TEXT,FILES,NETWORKS,DATABASES, ANDUNIMEDIA 333

11 ManipulatingTextwithMethodsandFiles 335

11.1TextasUnimedia335

11.2ManipulatingPartsofStrings336

11.2.1StringMethods:IntroducingObjectsandDotNotation337

11.2.2Lists:Powerful,StructuredText339

11.2.3StringsHaveNoFont341

11.3Files:PlacestoPutYourStringsandOtherStuff341

11.3.1OpeningandManipulatingFiles343

11.3.2GeneratingFormLetters344

11.3.3ReadingandManipulatingDatafromtheInternet345

11.3.4ScrapingInformationfromaWebPage348

11.3.5ReadingCSVData349

11.3.6WritingOutPrograms351

11.4ThePythonStandardLibrary352

11.4.1MoreonImportandYourOwnModules353

11.4.2AddingUnpredictablytoYourProgramwithRandom354

11.4.3ReadingCSVFileswithaLibrary356

11.4.4ASamplingofPythonStandardLibraries356

AdvancedTextTechniques:Web andInformation 361

12.1Networks:GettingOurTextfromtheWeb361

12.1.1AutomatingAccesstoCSVData365

12.1.2AccessingFTP367

13

12.2UsingTexttoShiftBetweenMedia368

12.3MovingInformationBetweenMedia371

12.4UsingListsasStructuredTextforMediaRepresentations374

12.5HidingInformationinaPicture375

12.5.1HidingaSoundInsideaPicture377

MakingTextfortheWeb 383

13.1HTML:TheNotationoftheWeb383

13.2WritingProgramstoGenerateHTML388

13.2.1MakingHomePages390

13.3Databases:APlacetoStoreOurText393

13.3.1RelationalDatabases395

13.3.2AnExampleRelationalDatabaseUsingHashTables396

13.3.3WorkingwithSQL399

13.3.4UsingaDatabasetoBuildWebPages401

4 MOVIES 407

14 CreatingandModifyingMovies 409

14.1GeneratingAnimations410

14.2WorkingwithVideoSource419

14.2.1VideoManipulatingExamples419

14.3BuildingaVideoEffectBottom-Up423

15 Speed 430

15.1FocusingonComputerScience430

15.2WhatMakesProgramsFast?430

15.2.1WhatComputersReallyUnderstand431

15.2.2CompilersandInterpreters432

15.2.3WhatLimitsComputerSpeed?436

15.2.4DoesItReallyMakeaDifference?438

15.2.5MakingSearchingFaster441

15.2.6AlgorithmsThatNeverFinishorCan’tBeWritten443

15.2.7WhyIsPhotoshopFasterthanJES?444

15.3WhatMakesaComputerFast?444

15.3.1ClockRatesandActualComputation445

15.3.2Storage:WhatMakesaComputerSlow?446

15.3.3Display447

16 FunctionalProgramming 450

16.1UsingFunctionstoMakeProgrammingEasier450

16.2FunctionalProgrammingwithMapandReduce454

16.3FunctionalProgrammingforMedia457

16.3.1MediaManipulationwithoutChangingState458

16.4Recursion:APowerfulIdea459

16.4.1RecursiveDirectoryTraversals464

16.4.2RecursiveMediaFunctions466

17 Object-OrientedProgramming 471

17.1HistoryofObjects471

17.2WorkingwithTurtles473

17.2.1ClassesandObjects473

17.2.2SendingMessagestoObjects474

17.2.3ObjectsControlTheirState476

17.3TeachingTurtlesNewTricks478

17.3.1OverridinganExistingTurtleMethod480

17.3.2WorkingwithMultipleTurtlesatOnce481

17.3.3TurtleswithPictures483

17.3.4DancingTurtles484

17.3.5RecursionandTurtles487

17.4AnObject-OrientedSlideShow488

17.4.1MakingtheSlideClassMoreObject-Oriented491

17.5Object-OrientedMedia493

17.6JoetheBox498

17.7WhyObjects?499

APPENDIX 506

A QuickReferencetoPython 506

A.1Variables506

A.2FunctionCreation507

A.3LoopsandConditionals507

A.4OperatorsandRepresentationFunctions508

A.5NumericFunctions509

A.6SequenceOperations509

A.7StringEscapes509

A.8UsefulStringMethods509

A.9Files510

A.10Lists510

A.11Dictionaries,HashTables,orAssociativeArrays510

A.12ExternalModules510

A.13Classes511

A.14FunctionalMethods511

Bibliography512

Index515

Prefaceforthe FourthEdition

WestartedMediaComputationintheofSummer2002,andtaughtitfortheﬁrsttime inSpring2003.It’snowovertenyearslater,whichisagoodtimetosummarizethe changesacrossthesecond,third,andfourtheditions.

MediaComputationhasbeenusedsuccessfullyinanundergraduatecourseatGeorgiaTechforthelastdozenyears.Thecoursecontinuestohavehighretentionrates(over 85%ofstudentscompletetheclasswithapassinggrade),andismajorityfemale.Both studentsandteachersreport enjoying thecourse,whichisanimportantrecommendation forit.

ResearchershavefoundthatMediaComputationworksinavarietyofcontexts. TheUniversityofIllinois-ChicagohadtheﬁrstMediaComputationpaperoutsideof Georgia,andtheyshowedhowswitchingtoMediaCompimprovedtheirretention ratesinclassesthatweremuchmorediversethanthoseatGeorgiaTech[41].The UniversityofCalifornia-SanDiegoadoptedMediaComputationaspartofabigchange intheirintroductorycourse,wheretheyalsostartedusingpair-programmingandpeer instruction.Theirpaperatthe2013SIGCSESymposiumshowedhowthesechanges ledtodramaticimprovementsinstudentretention,evenmeasuredayearlaterinthe Sophomoreyear.ThepaperalsowontheBestPaperawardattheconference[27]. It’sbeenparticularlydelightfultoseeMediaComputationadoptedandadaptedfor newsettings,likeCynthiaBaileyLee’screationofaMATLABMediaComputation curriculum[12].

Markwroteapaperin2013,summarizingtenyearsofMediaComputationresearch. MediaComputationdoesoftenimproveretention.Ourdetailedinterviewstudieswith femalestudentssupportstheclaimthattheyﬁndtheapproachtobecreativeandengaging,andthat’swhatkeepsthestudentsintheclass.ThatpaperwontheBestPaperaward atthe2013InternationalComputingEducationResearch(ICER)Conference[33].

HOWTOTEACHMEDIACOMPUTATION

Overthelast10years,wehavelearnedsomeoftheapproachesthatworkbestfor teachingMediaComputation.

• Letthestudentsbecreative. ThemostsuccessfulMediaComputationclasses useopen-endedassignmentsthatletthestudentschoosewhatmediatheyuse. Forexample,acollageassignmentmightspecifytheuseofparticularﬁltersand compositions,butallowforthestudenttochooseexactlywhatpicturesareused. Theseassignmentsoftenleadtothestudentsputtinginalotmoretimetoget just thelookthattheywanted,andthatextratimecanleadtoimprovedlearning.

• Letthestudentssharewhattheyproduce. Studentscanproducesomebeautiful pictures,sounds,andmoviesusingMediaComputation.Thoseproductsaremore motivatingforthestudentswhentheygettosharethemwithothers.Someschools provideonlinespaceswherestudentscanpostandsharetheirproducts.Other schoolshaveevenprintedstudentworkandheldanartgallery.

• Codeliveinfrontoftheclass. Thebestpartoftheteacheractuallytypingincode infrontoftheclassisthat nobody cancodeforlonginfrontofanaudienceand not makeamistake.Whentheteachermakesamistakeandﬁxesit,thestudents see(a)thaterrorsareexpectedand(b)thereisaprocessforﬁxingthem.Coding livewhenyouareproducingimagesandsoundsisfun,andcanleadtounexpected resultsandtheopportunitytoexplore,“Howdid that happen?”

• Pairprogrammingleadstobetterlearningandretention. Theresearchresultson pairprogrammingaretremendous.Classesthatusepairprogramminghavebetter retentionresults,andthestudentslearnmore.

• Peerinstructionisgreat. Notonlydoespeerinstructionleadtobetterlearning andretentionoutcomes,butitalsogivestheteacherbetterfeedbackonwhatthe studentsarelearningandwhattheyarestrugglingwith.Westronglyencourage theuseofpeerinstructionincomputingclasses.

• Workedexampleshelpwithcreativitylearning. Mostcomputerscienceclasses donotprovideanywherenearlyenoughworked-outexamplesforstudentsto learnfrom.Studentsliketolearnfromexamples.OneofthebeneﬁtsofMedia Computationisthatweprovidealotofexamples(we’venevertriedtocountthe numberof for and if statementsinthebook!), and it’seasytoproducemore ofthem.Inclass,wedoanactivitywherewehandoutexampleprograms,then showaparticulareffect.Weaskpairsorgroupsofstudentstoﬁgureoutwhich programgeneratedthateffect.Thestudentstalkaboutcode,andstudyabunchof examples.

APCSPRINCIPLES

TheAdvancedPlacementexaminCSPrinciples1 hasnowbeendeﬁned.Wehave explicitlywrittenthefourtheditionwithCSPrinciplesinmind.Forexample,weshow howtomeasurethespeedofaprogramempiricallyinordertocontrasttwoalgorithms (LearningObjective4.2.4),andweexploremultiplewaysofanalyzingCSVdatafrom theInternet(LearningObjectives3.1.1,3.2.1,and3.2.2).

Overall,weaddresstheCSPrincipleslearningobjectivesexplicitlyinthisbookas shownbelow:

• In BigIdeaI:Creativity :

• LO1.1.1: usecomputingtoolsandtechniquestocreateartifacts.

• LO1.2.1: usecomputingtoolsandtechniquesforcreativeexpression.

1 http://apcsprinciples.org

• LO1.2.2: ... createacomputationalartifactusingcomputingtoolsandtechniques tosolveaproblem.

• LO1.2.3: createanewcomputationalartifactbycombiningormodifying existingartifacts.

• LO1.2.5: ... analyzethecorrectness,usability,functionality,andsuitabilityof computationalartifacts.

• LO1.3.1: ... useprogrammingasacreativetool.

• In BigIdeaII:Abstraction:

• LO2.1.1: ... describethevarietyofabstractionsusedtorepresentdata.

• LO2.1.2: ... explainhowbinarysequencesareusedtorepresentdigitaldata.

• LO2.2.2: ... usemultiplelevelsofabstractionincomputation.

• LO2.2.3: ... identifymultiplelevelsofabstractionsbeingusedwhenwriting programs.

• In BigIdeaIII:Dataandinformation:

• LO3.1.1: ... usecomputerstoprocessinformation,ﬁndpatterns,andtest hypothesesaboutdigitallyprocessedinformationtogaininsightandknowledge.

• LO3.2.1: ... extractinformationfromdatatodiscoverandexplainconnections, patterns,ortrends.

• LO3.2.2: ... uselargedatasetstoexploreanddiscoverinformationandknowledge.

• LO3.3.1: analyzehowdatarepresentation,storage,security,andtransmission ofdatainvolvecomputationalmanipulationofinformation.

• In BigIdeaIV:Algorithms:

• LO4.1.1: ... developanalgorithmdesignedtobeimplementedtorunona computer.

• LO4.1.2: ... expressanalgorithminalanguage.

• LO4.2.1: ... explainthedifferencebetweenalgorithmsthatruninareasonable timeandthosethatdonotruninareasonabletime.

• LO4.2.2: explainthedifferencebetweensolvableandunsolvableproblems incomputerscience.

• LO4.2.4: ... evaluatealgorithmsanalyticallyandempiricallyforefﬁciency, correctness,andclarity.

• In BigIdeaV:Programming:

• LO5.1.1: ... developaprogramforcreativeexpression,tosatisfypersonal curiosityortocreatenewknowledge.

• LO5.1.2: developacorrectprogramtosolveproblems.

• LO5.2.1: explainhowprogramsimplementalgorithms.

• LO5.3.1: ... useabstractiontomanagecomplexityinprograms.

• LO5.5.1: ... employappropriatemathematicalandlogicalconceptsinprogramming.

• In BigIdeaVI:TheInternet :

• LO6.1.1: explaintheabstractionsintheInternetandhowtheInternetfunctions.

CHANGESINTHEFOURTHEDITION

1. Wefixedlotsofbugsthatourcrackbug-findersidentifiedinthethirdedition.

2. Wechangedmostofthepicturesinthebook–theyweregettingstale,andourkids wantedustonotuseasmanypicturesofthem.

3. Weaddedmoreend-of-chapterquestions.

4. Weaddedawholenewchapter,ontextasamediumandmanipulatingstrings (tomakesentences,koans,andcodes).Thisisn’ta necessary chapter(e.g.,we introduce for and if statements,butwedidn’tremovetheintroductionslaterin thebook).Forsomeofourteachers,playingwithtextwithshorterloops(iterating overallthecharactersinasentenceistypicallysmallerthanthethousandsofpixels inapicture)isamorecomfortablewaytostart.

5. WegaveupﬁghtingthebattleofinventingaWebscraperthatcouldbeatoutthe changesthatFacebookmade,whichkeptbreakingtheoneweputinthe3rdedition andthenkeptupdatingontheteacher’swebsite2 .Instead,wewroteexamplesin thisbookforprocessingCSV(Comma-SeparatedValues),acommonformatfor sharingdataontheInternet.WeparsetheCSVfromaﬁleusingstringprocessing, thenusingtheCSVlibraryinPython,andthenaccessingthedatabyURL.

6. Weaddedsomenewedgedetectioncodewhichisshorterandsimplertounderstand.

7. Weaddedmorewithturtles:creatingdancingturtles(using sleep fromthe time moduletopauseexecution)andrecursivepatterns.

8. WeupdatedthebooktousethelatestfeaturesinJES,whichincludethosethat reducetheneedtousefullpathnames(aproblemidentiﬁedbyStephenEdwards andhisstudentsintheirSIGCSE2014paper[43]).

ACKNOWLEDGMENTS

Oursincerethanksgoouttoallourreviewersandbug-ﬁnders:

• AtthetopofthelistisSusanSchwarzoftheUSMilitaryAcademyatWestPoint. Susanrunsalargecoursewithmanyinstructors,andpayscarefulattentionto what’sgoinginallofthesectionsofthecourse.Sheturnedthatattentionon thethirdeditionofthisbook.Shecaughtmanybugs,andgaveuslotsofuseful feedback.Thanks,Susan!

2 http://home.cc.gatech.edu/mediaComp and http://www.mediacomputation.org

• OurotherbugﬁndersforthebookwereJohnRutkiewicz,U.Massachusetts–Dartmouth;BrianDorn,U.Nebraska–Omaha;DaveLargent,BallStateUniversity;Simon,UniversityofNewcastle;EvaHeinrich,MasseyUniversity;Peter J.DePasquale,TheCollegeofNewJersey,andBillLeahy,GeorgiaInstituteof Technology.

• MatthewFrazier,NorthCarolinaStateUniversity,workedwithusinthesummer of2014tocreateanewversionofJES–ﬁxingmanybugs,andimprovingJES considerably.

• Wearegratefulforthefeedbackfromourbookreviewersforthe4thedition: AndrewCencini,BenningtonCollege;SusanFox,MacalesterCollege;Kristin Lamberty,UniversityofMinnesota-Morris;JeanSmith,TechnicalCollegeofthe Lowcountry;andWilliamT.Verts,UniversityofMassachusetts-Amherst.

• Wearegratefulfortheinputfromourbookreviewersforthe3rdedition,too: JosephOldham,CentreCollege;LukaszZiarek,PurdueUniversity;Joseph O’Rourke,SmithCollege;AtulPrakash,UniversityofMichigan;NoahD.Barnette,VirginiaTech;AdelaidaA.Medlock,DrexelUniversity;SusanE.Fox, MacalesterCollege;DanielG.Brown,UniversityofWaterloo;BrianA.Malloy, ClemsonUniversity;ReneeRenner,CaliforniaStateUniversity,Chico.

MarkGuzdialandBarbaraEricson GeorgiaInstituteofTechnology

PrefacetotheFirstEdition

Researchincomputingeducationmakesitclearthatonedoesn’tjust“learntoprogram.” Onelearnstoprogram something [8,19],andthemotivationtodothatsomethingcan makethedifferencebetweenlearningandnotlearningtoprogram[5].Thechallenge foranyteacheristopicka something thatisapowerfulenoughmotivator.

Peoplewanttocommunicate.Wearesocialcreaturesandthedesiretocommunicate isoneofourprimalmotivations.Increasingly,thecomputerisusedasatoolforcommunicationevenmorethanatoolforcalculation.Virtuallyallpublishedtext,images, sounds,music,andmoviestodayarepreparedusingcomputingtechnology.

Thisbookisaboutteachingpeopletoprograminordertocommunicatewithdigital media.Thebookfocusesonhowtomanipulateimages,sounds,text,andmoviesas professionalsmight,butwithprogramswrittenbystudents.Weknowthatmostpeople willuseprofessional-gradeapplicationstoperformthesetypeofmanipulations.But, knowing how towriteyourownprogramsmeansthatyou can domorethanwhatyour currentapplicationallowsyoutodo.Yourpowerofexpressionisnotlimitedbyyour applicationsoftware.

Itmayalsobetruethatknowinghowthealgorithmsinamediaapplicationswork allowsyoutousethembetterortomovefromoneapplicationtothenextmoreeasily. Ifyourfocusinanapplicationisonwhatmenuitemdoeswhat,everyapplicationis different.Butifyourfocusisonmovingorcoloringthepixelsinthewayyouwant, thenmaybeit’seasiertogetpastthemenuitemsandfocusonwhatyouwanttosay.

Thisbookisnotjustaboutprogramminginmedia.Media-manipulationprograms canbehardtowriteormaybehaveinunexpectedways.Naturalquestionsarise,like “WhyisthesameimageﬁlterfasterinPhotoshop?”and“Thatwashardtodebug—Are therewaysofwritingprogramsthatare easier todebug?”Answeringquestionslike theseiswhatcomputerscientistsdo.Thereareseveralchaptersattheendofthebook thatareabout computing,notjustprogramming.Theﬁnalchaptersgobeyondmedia manipulationtomoregeneraltopics.

Thecomputeristhemostamazinglycreativedevicethathumanshaveeverconceived. Itiscompletelymadeupofmind-stuff.Thenotion“Don’tjustdreamit,beit”isreally possibleonacomputer.Ifyoucanimagineit,youcanmakeit“real”onthecomputer. Playingwithprogrammingcanbeand should beenormousfun.

OBJECTIVES,APPROACHANDORGANIZATION

Thecurricularcontentofthisbookmeetstherequirementsofthe“imperative-ﬁrst” approachdescribedintheACM/IEEE ComputingCurriculum2001 standardsdocument [2].Thebookstartswithafocusonfundamentalprogrammingconstructs:assignments, sequentialoperations,iteration,conditionals,anddeﬁningfunctions.Abstractions

(e.g.,algorithmiccomplexity,programefﬁciency,computerorganization,hierarchicaldecomposition,recursion,andobject-orientedprogramming)areemphasizedlater, afterthestudentshaveacontextforunderstandingthem.

Thisunusualorderingisbasedontheﬁndingsofresearchinthelearningsciences. Memoryisassociative.Weremembernewthingsbasedonwhatweassociatethemwith. Peoplecanlearnconceptsandskillsonthepremisethattheywillbeusefulsomedaybut theconceptsandskillswillberelatedonlytothepremises.Theresulthasbeendescribed as“brittleknowledge”[25]—thekindofknowledgethatgetsyouthroughtheexam butispromptlyforgottenbecauseitdoesn’trelatetoanythingbutbeinginthatclass.

Conceptsandskillsarebestrememberediftheycanberelatedtomanydifferent ideasortoideasthatcomeupinone’severydaylife.Ifwewantstudentstogain transferable knowledge(knowledgethatcanbeappliedinnewsituations),wehaveto helpthemtorelatenewknowledgetomoregeneralproblems,sothatthememoriesget indexedinwaysthatassociatewiththosekindsofproblems[22].Inthisbook,weteach withconcreteexperiencesthatstudentscanexploreandrelateto(e.g.,conditionalsfor removingred-eyeinpictures)andlaterlayabstractionsontopofthem(e.g.,achieving thesamegoalusingrecursionorfunctionalﬁltersandmaps).

Weknowthatstartingfromtheabstractionsdoesn’treallyworkforcomputing students.AnnFleuryhasshownthatstudentsinintroductorycomputingcoursesjust don’tbuywhatwetellthemaboutencapsulationandreuse(e.g.,[7]).Studentsprefer simplercodethattheycantraceeasilyandtheyactuallythinkthatsuchcodeis better. Ittakestimeandexperienceforstudentstorealizethatthereisvalueinwell-designed systems.Withoutexperience,it’sverydifﬁcultforstudentstolearntheabstractions.

The mediacomputation approachusedinthisbookstartsfromwhatmanypeople usecomputersfor:imagemanipulation,exploringdigitalmusic,viewingandcreating Webpages,andmakingvideos.Wethenexplainprogrammingandcomputinginterms oftheseactivities.WewantstudentstovisitAmazon(forexample)andthink,“Here’s acatalogWebsite—andIknowthattheseareimplementedwithadatabaseanda setofprogramsthatformatthedatabaseentriesasWebpages.”Wewantstudentsto useAdobePhotoshopandGIMPandthinkabouthowtheirimageﬁltersareactually manipulatingred,green,andbluecomponentsofpixels.Startingfromarelevantcontext makestransferofknowledgeandskillsmorelikely.Italsomakestheexamplesmore interestingandmotivating,whichhelpswithkeepingstudentsintheclass.

Themediacomputationapproachspendsabouttwo-thirdsofthetimeongiving studentsexperienceswithavarietyofmediaincontextsthattheyﬁndmotivating.After thattwo-thirds,though,theynaturallystarttoaskquestionsabout computing.“Whyis itthatPhotoshopisfasterthanmyprogram?”and“Moviecodeisslow—Howslowdo programsget?”aretypical.Atthatpoint,weintroducetheabstractionsandthevaluable insightsfromcomputersciencethatanswer their questions.That’swhatthelastpart ofthisbookisabout.

Adifferentbodyofresearchincomputingeducationexploreswhywithdrawalor failureratesinintroductorycomputingaresohigh.Onecommonthemeisthatcomputingcoursesseem“irrelevant”andunnecessarilyfocuson“tediousdetails”such asefﬁciency[21,1].Acommunicationscontextisperceivedasrelevantbystudents

(astheytellusinsurveysandinterviews[6,18]).Therelevantcontextispartofthe explanationforthesuccesswehavehadwithretentionintheGeorgiaTechcoursefor whichthisbookwaswritten.

Thelateentranceofabstractionisn’ttheonlyunusualorderinginthisapproach.We startusingarraysandmatricesinChapter3,inourfirstsignificantprograms.Typically, introductorycomputingcoursespusharraysoffuntillater,becausetheyareobviously morecomplicatedthanvariableswithsimplevalues.Arelevantandconcretecontext isverypowerful[19].Wefindthatstudentshavenoproblemmanipulatingmatricesof pixelsinapicture.

Therateofstudentswithdrawingfromintroductorycomputingcoursesorreceiving aDorFgrade(commonlycalledthe WDFrate)isreportedinthe30–50%rangeor evenhigher.Arecentinternationalsurveyoffailureratesinintroductorycomputing coursesreportedthattheaveragefailurerateamong54U.S.institutionswas33%and among17internationalinstitutionswas17%[24].AtGeorgiaTech,from2000to2002, wehadanaverageWDFrateof28%intheintroductorycourserequiredforallmajors. Weusedtheﬁrsteditionofthistextinourcourse IntroductiontoMediaComputation. Ourﬁrstpilotofferingofthecoursehad121students,nocomputingorengineering majors,andtwo-thirdsofthestudentswerefemale.OurWDFratewas11.5%.

Overthenexttwoyears(Spring2003toFall2005),theaverageWDFrateatGeorgia Tech(acrossmultipleinstructors,andliterallythousandsofstudents)was15%[29]. Actually,the28%priorWDFrateand15%currentWDFrateareincomparable,since allmajorstookthefirstcourseandonlyliberalarts,architecture,andmanagement majorstookthenewcourse.Individualmajorshavemuchmoredramaticchanges. Managementmajors,forexample,hada51.5%WDFratefrom1999to2003withthe earliercourse,andhada11.2%failurerateinthefirsttwoyearsofthenewcourse[29]. Sincethefirsteditionofthisbookwaspublished,severalotherschoolshaveadopted andadaptedthisapproachandevaluatedtheirresult.Allofthemhavereportedsimilar, dramaticimprovementsinsuccessrates[4,42].

WaystoUseThisBook

ThisbookrepresentswhatweteachatGeorgiaTechinprettymuchthesameorder. Individualteachersmayskipsomesections(e.g.,thesectiononadditivesynthesis, MIDI,andMP3),butallofthecontentherehasbeentestedwithourstudents. However,thismaterialhasbeenusedinmanyotherways.

• AshortintroductiontocomputingcouldbetaughtwithjustChapters2(introductiontoprogramming)and3(introductiontoimageprocessing),perhapswith somematerialfromChapters4and5.Wehavetaughtevensingle-dayworkshops onmediacomputationusingjustthismaterial.

• Chapters6through8basicallyreplicatethecomputerscienceconceptsfrom Chapters3through5butinthecontextofsoundsratherthanimages.Weﬁnd thereplicationuseful—somestudentsseemtorelatebettertotheconceptsof iterationandconditionalswhenworkingwithonemediumthanwiththeother.

Further,itgivesustheopportunitytopointoutthatthesame algorithm canhave similareffectsindifferentmedia(e.g.,scalingapictureupordownandshiftinga soundhigherorlowerinpitcharethesamealgorithm).Butitcouldcertainlybe skippedtosavetime.

• Chapter12(onmovies)introducesnonewprogrammingorcomputingconcepts. Whilemotivational,movieprocessingcouldbeskippedtosavetime.

• Werecommendgettingtoatleastsomeofthechaptersinthelastunit,inorderto leadstudentsintothinkingaboutcomputingandprogramminginamoreabstract manner,butclearlynot all ofthechaptershavetobecovered.

PythonandJython

TheprogramminglanguageusedinthisbookisPython.Pythonhasbeendescribedas “executablepseudo-code.”Wehavefoundthatbothcomputersciencemajorsandnon majorscanlearnPython.SincePythonisactuallyusedforcommunicationstasks(e.g., Websitedevelopment),it’sarelevantlanguageforanintroductorycomputingcourse. Forexample,jobadvertisementspostedtothePythonWebsite(http://www.python. org)showthatcompanieslikeGoogleandIndustrialLight&MagichirePythonprogrammers.

ThespeciﬁcdialectofPythonusedinthisbookis Jython (http://www.jython. org).Jython is Python.ThedifferencesbetweenPython(normallyimplementedinC) andJython(whichisimplementedinJava)areakintothedifferencesbetweenany twolanguageimplementations(e.g.,Microsoftvs.GNUC++ implementations)—the basiclanguageis exactly thesame,withsomelibraryanddetailsdifferencesthatmost studentswillnevernotice.

TYPOGRAPHICALNOTATIONS

ExamplesofPythoncodelooklikethis: x=x+1.Longerexampleslooklikethis: defhelloWorld(): print "Hello,world!"

WhenshowingsomethingthattheusertypesinwithPython’sresponse,itwillhave asimilarfontandstyle,buttheuser’stypingwillappearafteraPythonprompt(>>>): >>> print 3+4

UserinterfacecomponentsofJES(JythonEnvironmentforStudents)willbespeciﬁedusingasmallcapsfont,like Save menuitemandthe Load button. Thereareseveralspecialkindsofsidebarsthatyou’llﬁndinthebook.

ComputerScienceIdea: AnExampleIdea Keycomputerscienceconceptsappearlikethis.

CommonBug: AnExampleCommonBug

Commonthingsthatcancauseyourprogramtofailappearlikethis.

DebuggingTip: AnExampleDebuggingTip

Ifthere’sagoodwaytokeepabugfromcreepingintoyourprogramsintheﬁrstplace, it’shighlightedhere.

MakingItWorkTip: AnExampleHowtoMakeItWork Bestpracticesortechniquesthatreallyhelparehighlightedlikethis.

INSTRUCTORRESOURCES

TheinstructorresourcesareavailableonthePearsonEducation’sInstructorResource Centerat www.pearsonglobaleditions.com/guzdial:

• PowerPoint Presentationslides

ACKNOWLEDGMENTS

Oursincerethanksgoouttothefollowing:

• JasonErgle,ClaireBailey,DavidRaines,andJoshuaSklare,whomadetheinitial versionofJESwithsurprisingqualityinanamazinglyshortamountoftime.Over theyears,AdamWilson,LarryOlson,YuCheung(Toby)Ho,EricMickley,Keith McDermott,EllieHarmon,TimmyDouglas,AlexRudnick,BrianO’Neill,and WilliamFredrick(Buck)ScharfnorthIIIhavemadeJESintotheusefulandstill understandabletoolthatitistoday.

• AdamWilsonbuilttheMediaToolsthataresousefulforexploringsoundsand imagesandprocessingvideo.

• AndreaForte,MarkRichman,MattWallace,AlisaBandlow,DerekChambless, LarryOlson,andDavidRenniehelpedbuildcoursematerials.Derek,Mark,and Mattcreatedmanyexampleprograms.

• TherewereseveralpeoplewhoreallymadetheeffortcometogetheratGeorgia Tech.BobMcMath,Vice-ProvostatGeorgiaTech,andJimFoley,AssociateDean forEducationintheCollegeofComputing,investedinthiseffortearlyon.Kurt Eiseltworkedhardtomakethiseffortreal,convincingotherstotakeitseriously. JanetKolodnerandAaronBobickwereexcitedandencouragingabouttheidea ofmediacomputationforstudentsnewtocomputerscience.JeffPiercereviewed

andadvisedusonthedesignofthemediafunctionsusedinthebook.Aaron Lantermangavemelotsofadviceonhowtoconveythedigitalmaterialcontent accurately.JoanMorton,ChrissyHendricks,DavidWhite,andallthestaffofthe GVUCentermadesurethatwehadwhatweneededandthatthedetailswere handledtomakethiseffortcometogether.AmyBruckmanandEugeneGuzdial boughtMarktimetogettheﬁnalversioncompleted.

• WearegratefultoColinPottsandMonicaSweatwhohavetaughtthisclassat GeorgiaTechandgivenusmanyinsightsaboutthecourse.

• CharlesFowlerwastheﬁrstpersonoutsideofGeorgiaTechwillingtotakethe gambleandtrialthecourseinhisowninstitution(GainesvilleCollege),forwhich we’reverygrateful.

• ThepilotcourseofferedinSpring2003atGeorgiaTechwasveryimportantin helpingusimprovethecourse.AndreaForte,RachelFithian,andLaurenRichdid theassessmentofthepilotofferingofthecourse,whichwasincrediblyvaluablein helpingusunderstandwhatworkedandwhatdidn’t.Theﬁrstteachingassistants (JimGruen,AngelaLiang,LarryOlson,MattWallace,AdamWilson,andJose Zagal)didalottohelpcreatethisapproach.BlairMacIntyre,ColinPotts,and MonicaSweathelpedmakethematerialseasierforotherstoadopt.JochenRick madetheCoWeb/SwikiagreatplaceforCS1315studentstohangout.

• Manystudentspointedouterrorsandmadesuggestionstoimprovethebook. ThankstoCatherineBilliris,JenniferBlake,KarinBowman,MaryamDoroudi, SuzannahGill,BaillieHomire,JonathanLaing,MireilleMurad,MichaelShaw, SummarShoaib,andespeciallyJonathanLonghitano,whohasarealﬂairfor copyediting.

• Thankstoformer MediaComputation studentsConstantinoKombosch,Joseph Clark,andShannonJoinerforpermissiontousetheirsnapshotsfromclassin examples.

• TheresearchworkthatledtothistextwassupportedbygrantsfromtheNational ScienceFoundation—fromtheDivisionofUndergraduateEducation,CCLIprogram,andfromtheCISEEducationalInnovationsprogram.Thankyouforthe support.

• ThankstocomputingstudentsAnthonyThomas,CelinesRivera,andCarolina Gomezforallowingustousetheirpictures.

• Finallybutmostimportant,thankstoourchildrenMatthew,Katherine,andJennifer Guzdial,whoallowedthemselvestobephotographedandrecordedforMommy andDaddy’smediaprojectandwhoweresupportiveandexcitedabouttheclass.

MarkGuzdialandBarbaraEricson GeorgiaInstituteofTechnology PearsonwouldliketothankandacknowledgeDheerajD.,REVAInstituteofTechnologyandManagementKattigenahalli,SomitraSanadhya,IndianInstituteofTechnology Delhi,andSimon,UniversityofNewcastle,forcontributingtotheGlobalEdition,and ShaligramPrajapat,DeviAhilyaUniversityIndore,NgHu,MultimediaUniversity, RohitTahiliani,RenjithS.,andShivaniPandit,forreviewingtheGlobalEdition.

AbouttheAuthors

MarkGuzdial isaprofessorintheSchoolofInteractiveComputingintheCollege ofComputingatGeorgiaInstituteofTechnology.Heisoneofthefoundersofthe ACM’sInternationalComputingEducationResearchworkshopseries.Dr.Guzdial’s researchfocusesonlearningsciencesandtechnology,specifically,computingeducation research.HisfirstbookswereontheprogramminglanguageSqueakanditsusein education.Hewastheoriginaldeveloperof“Swiki”(SqueakWiki),thefirstwiki developedexplicitlyforuseinschools.HeisaFellowandaDistinguishedEducator oftheACM.Heisontheeditorialboardsofthe JournaloftheLearningSciences and CommunicationsoftheACM. Hewasarecipientofthe2012IEEEComputerSociety UndergraduateTeachingAward.

BarbaraEricson isaresearchscientistandthedirectorofComputingOutreachfor theCollegeofComputingatGeorgiaTech.Shehasbeenworkingonimprovingintroductorycomputingeducationsince2004.

ShehasservedastheteachereducationrepresentativeontheComputerScience TeachersAssociationboard,theco-chairoftheK-12AlliancefortheNationalCenter forWomeninInformationTechnology,andasareaderfortheAdvancedPlacement ComputerScienceexams.Sheenjoysthediversityofthetypesofproblemsshehas workedonovertheyearsincomputingincludingcomputergraphics,artiﬁcialintelligence,medicine,andobject-orientedprogramming.

MarkandBarbarareceivedthe2010ACMKarlV.KarlstromAwardforOutstanding ComputerEducatorfortheirworkonMediaComputationincludingthisbook.Theyled aprojectcalled“GeorgiaComputes!”forsixyears,whichhadasigniﬁcantimpactin improvingcomputingeducationintheUSstateofGeorgia[31].Together,theyMark andBarbaraareleadersinthe ExpandingComputingEducationPathways (ECEP) alliance3

3 http://www.ecepalliance.org

PART 1 INTRODUCTION

Chapter1IntroductiontoComputerScience andMediaComputation

Chapter2IntroductiontoProgramming

Chapter3CreatingandModifyingText

Chapter4ModifyingPicturesUsingLoops

Chapter5PictureTechniqueswithSelection

Chapter6ModifyingPixelsbyPosition