INTRODUCTIONTOPROGRAMMINGWITHPYTHON:

VIVIANBAILEY

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TABLEOFCONTENTSTableofContents

Chapter1.WhyYouShouldLearnProgramming

Chapter2.WhyPythonisthePerfectLanguage

Chapter3.GettingStarted:Pre-reqs

Chapter4.Variables,Expressions,Statement,Strings

Chapter5.Functions

Chapter6.Conditionals,FlowControl,Decisions

Chapter7.Iterations

Chapter8.Lists,Dictionaries,Tuples

Chapter9.ObjectOrientedProgramming

Chapter10.Classes,Objects,Inheritance

Chapter11.Debugging

Chapter12.Nextup

WHYTHISBOOK?

Theadage“penismightierthansword”isbestservedbyprogramminglanguages.Youliterallytypeandcommunicatesolutionstoproblemsonacomputer,anditcomestolife.

ThisbookintroducesPython,thesimplestandcurrentlyoneofthemostpowerfulObjectOrientedProgramminglanguagesontheplanet.ThebookshowshowitissimilartolearninganewdialectofEnglish,onemeantforthecomputingdevicesyouholdinyourhands.

ItwillintroduceyoutothebasicsofPythonlanguage:itsfundamentalbuildingblocks,theirsyntax,theirbasicuses,andhowtheyarerelatedtooneanotherincreatinglargercodes.

Thisbookismeantfornovicesandbeginners.Hence,itusessimplereallifeexamples,offersshortcodeswithexplanations,andcontinuouslylinksbacktoearlierchaptersandbuildsonthem.

CHAPTER1.WHYYOUSHOULDLEARNPROGRAMMING

Theriseofsmartdevices,wirelessconnectivity,andincreasedusermobilityinofficesmadecomputersanintegralpartofourlifestyles.Asourrelianceonsmartdevicesandvariousappstocompleteadiverserangeofactivitiesincreases,learningtocodeisbecomingakintolearningasecondlanguage.

Normally,welearnsecondlanguagestoincreaseourreach,overcomegeographicandculturalbarriers,andtobeabletocommunicatewithpeoplefromdiversecultures.Smartdeviceshavebroughtdownbarriersacrossdifferentcultures,andhavebecomeoneofourmosttrustedcompanions.However,wearenotabletoeffectivelycommunicateandinstructoursmartcompanionstoperformtheactionsthatwedesire.

Learningtoeffectivelycommunicatewithcomputersandsmartdevices,andbeingabletoinstructthemtoperformdifferenttasksisfastbecomingsomethingmorethananaddedskill—itisbecomingpartofwhatitmeanstobehumanintheageofDigitalNatives.

7REASONSFORLEARNINGTOPROGRAMLearntoprogramandyouwillbeabletoexperiencethefollowingseven,awe-inspiringrealitiesofbeingaDigitalNative.

IT’STHEONLYTIMEWHENWRITINGCANLITERALLYSOLVEPROBLEMSTheadage“penismightierthansword”isbestservedbyprogramminglanguages.Youliterallytypeandcommunicatesolutionstoaproblemonacomputer,anditcomestolife.

It’samazingtorealizehowpowerfulthisformofcommunicationis.MostofsmartphoneusershavevisitedAppStoresandseenarangeofapps,eachsolvingauniqueproblemforus.Knowingaprogramminglanguagemeansthatyoucanbreakaproblemintosmallerproblemsandcreateprogramsforyourselfandothers.Somanyproblems,nomatterhowtrivialcannowberesolvedsimplybywritingthemoutinaprogramminglanguage.

PROGRAMMINGTRANSFORMSYOURCOMPUTERANDSMARTPHONEINTOAPOWERHOUSEHumanslandedonthemoonrelyingoncomputingpoweratleasta1000timeslesspowerfulthanthecomputingpowerofoursmartphones.

By2016,over2billionpeoplewillbeusingsmartphonesacrosstheglobe.Justimaginewhatthisprocessingpowercanbeputtousefor.ImaginewhatyoucancreateanddeveloponyourPCforusewithyoursmartphones:personalizedapps,games,tools,andmore.

Thepossibilitiesareendless.

PROGRAMMINGSIMPLIFIESTASKSBYAUTOMATINGTHEMWeliveinaworldwhereefficiencyisthehallmarkofeverything.Nobodywantstoperformtediousandrepetitivetasksifyoucanpayforasolutionthatcanautomateit.Thisrangesfromofficetaskstopersonalones.

Bylearningtocode,youcancreatesimplescriptsthatsimplifytasks.ThinkofgeneratingmacrosinMicrosoftOffice(ExcelandWord)orscriptsthatsimplifytasksyouhavetoperformregularlyatworke.g.creatingfoldersforprojects,completingforms,creatingshortcuts,addingmorefeaturestoexistingsoftware,etc.

ITDEVELOPSYOURABILITYFORABSTRACTANDDISCIPLINEDTHINKINGInstructingcomputersrequiresthatgivethemstep-by-stepinstructionsthatlinkpre-determinedinputstoexpectedoutcomes.Tocommunicatetothecomputer,youhavetowriteinanexplicitlanguage,fromproblemtosolution.Thisrequiresbreakingdownabstractproblemsintosimplerones,andthenorganizingthemintoinputsandoutputs.

Programmingteachesyoutoorganizethoughtsandbreakdownaproblemintoconstituents,identifyingexternalfactorsandtriggers,andmappingastep-by-steprouteforcomputingtheinputsintooutputsi.e.intosimplerchunksofprogrammablecode.

Thistrainsyourmindtothinkclearlyandsystematically,filteringoutinformationthathasnobearingsonthesolution,andfindingthesimplestsolutiontotheproblem.

FUTUREJOBSWILLREQUIRESOFTWARESKILLCurrently,programmingmaybeaskilltoboastyourchancesofentryintothemarket,howeverasorganizationsfocusonincreasinginterdepartmentalcollaboration,theybegintopreferpeoplewithinter-disciplinaryskillsets.Inthelongrun,beingabletoprogramwillbecomeaskillneededtosurviveinthetechnologymarket.

BECAUSEIT’SNOTHARDTOLEARNIfyoucancomprehendEnglishlanguage,learningtoprogramissimplyamatteroflearningthelogicbehindprogrammingwords.Overtheyears,programminglanguageshavebecomemoreintuitive,utilizingcommandsthatclearlystatetheirpurposeandhenceallowyoutonearlyconstructsentences“If-Then”,“Else”,“Print”,“Switch”,arejustthemostcommonlyusedcommandsinprogramminglanguage.

Allyouhavetodoislearnthegrammar,andwithpracticeyouwillbeabletowritethoseshortessaysthatidentifytheproblem,itscomponentsandinputs,andtheoutputsforeachinput.

PROGRAMMINGHASGREATEARNINGPOTENTIALAsyougetbetteratprogramming,youcaneasilyleverageyourproblemsolvingskillstodevelopsoftwareforsale.Thisincludesworkingasafreelancer—buildingapps,developingcustomsoftware,creatinganddesigningwebsites,orhelpingclientscompletetasksusingexistingsoftwareandplatforms(MicrosoftExcelandWord,Flash,Java,etc.).

INCONCLUSION—PREPARETOLEARNProgrammingisanadd-ontoyourcurrentunderstandingoftheEnglishlanguage.Thinkofitasanewdialect,onethatyourcomputerandsmartdeviceunderstands,onethathasalotofbenefitsinthemodernworld,iseasytolearnandonethatwillsoonbecomeamusthavefordigitalnatives.

CHAPTER2.WHYPYTHONISTHEPERFECTLANGUAGE

Inanagewheremachinesarebecominghighlyintelligentandarecontinuouslysimplifyinghuman-machineinteractions,itonlymakessensetouseanintelligentprogramminglanguage.

ExistingstaticallytypedlanguagessuchasPascal,C,orothersubsetsofC++andJavaintroduceverbosesyntaxthatcloudtheactualprocessofproblemdecompositionanddesignofdatatypesthathavetobeprogrammed.

Hence,forsomeonewhodoesnotknowhowtocode,theselanguagesseemunnatural.Furthermore,theadditionalcomplexityofthesyntaxonlyslowsdownthepaceofingrainingthemethodologyofprogramming.

ThisiswherePythonbringsinthepowerofsimpleandconsistentsyntax,backedbyalargestandardlibrarywithrealproblems.

NotwithstandingtheriseinitspopularityinAmericancollegesasreportedbytheAssociationforComputingMachinery,PythonhaseffectivelyreplacedJavaasthefirstlanguageofchoiceforbuddingprogrammers.

SowhatismakingPythontheperfectlanguageaftertwodecadesofbeinginthefield?

#1—MINIMALSETUPInstallingandrunningPythonisextremelysimple.AllyouhavetodoisdownloadthefileandeitherrunitthroughtheTerminalprogram(forMac),orthePowerShellprogram(Windows),andLoandbehold!You’rerunningPython.

#2—WRITINGAPROGRAMISAKINTOWRITINGINENGLISH!Pythonisauniversallanguage.Thismeansthatitssyntaxandcodinglingoisexceptionallysimplifiedandeasy.

PythonistheclosestthingtowritingalogicalargumentinEnglish.Thecommandsaresimpleandtheadditionalbaggageofgrammar(programmingsyntaxsuchasbrackets,colons,quotes,etc)isminimal.Yougrasphowtosystematicallybreakdownaproblemintosimplersteps,andyoucaneasilycodeitinPython.

Inaphrase:agreatfirstexperienceforanybeginner.

Thestandardfirsthands-onprogrammingexperiencethatallbeginnersgothroughistoprintsomethingonthescreenusingcoding.Thisisnormallythewords“HelloWorld”,amongothers.

Pythonmakesitliterallyamatterofwritingasentence

print(“HelloWorld”)

Comparethistothefollowing(Java):

publicclassHelloWorld{

publicstaticvoidmain(String[]args){

System.out.println(“Hello,World”);

}

}

Furthermore,whenyoumoveaheadintothecourse,otherexamplesofsimplifiedprogrammingwillleapout,includingsimplereading/writingofinformation,stringprocessing,GUI’s,websitecode,Databases,websites,etc.

Itssimplicityandeaseofprogrammingisthereasonwhyithasbeenadoptedbysomanypeopleandforsuchawiderangeoftasks.Thisisfurthermadeenjoyablebythefactthataverylargecommunityofenthusiasticdevelopersisalwaysabuzztoaidnewcomersbecomeinitiatedintothefold.

#3—PYTHONISEASYTOREADPythonisdesignedtobeaneasyread.

“Readability”ofacodemayandseemunimportantrightnow,butitbecomesthedefiningfactorwhenthecodebecomeslargerandmorecomplex.

Readabilityisveryimportant,becauseunlikeacoursebook,thechapters(orchunksofcode)arenotalwaysarrangedtoworkinastep-by-steporlinearorder.Attimescodingblocksinthefarrecessesofthecodeneedtobecalledearlier,orlater,multipletimesthroughoutthecode,andsoon.

Easeofreadabilityisimportantforsharingacodebetweenateam,fortroubleshootingaprogram,andformakingchangestoit.Intraditionallanguages,readingbecomesincreasinglydifficultasbecauseofallthenon-Englishgrammaticalsyntax.

Pythonusesindentationtogivestructuretothecode,andthoughprogrammerswhoaremigratingfromadifferentlanguagetoPythonmaybeheardcomplainingaboutthelack(andnearabsence)ofbraces,itisoneofthekeybenefitsofPython:itsimplyde-clutterstheworkenvironment!

Thinkofindentationsliketheheadingsinyourwordprocessingsoftware(H1,H2,H3,H4,H5,andsoon).Incodingtheheadingsarenormallycurlybrackets(“{}”)thathavetobeaddedatthestartandendoftheparagraph.

Asaresult,twotypesofcommunicationarehappeningsimultaneously:bracestotellthemachineabouttheprogram,andtheindentationstotellthereader(anotherprogrammer)whattheprogramisabout.

NowimagineNOThavingtoaddbracketsandindentationandfollowalegendyouhavecreatedearliertokeepyourprogramreadable.Pythondoesthisbyofferingasinglestructuretodenoteaprogram:makingiteasierforhumansandcomputersaliketoreaditwithease.

#4—YOUDONOTHAVETOCOMPILETHEPROGRAMTORUNITWhenyou’relearningsomethingnew,mistakesareboundtohappen.Howthosemistakesareshowntoyouoftenplaysacrucialroleinhowmotivatedyouaretotryagain,orhowaffectedyouarebythemistakethatyouhavemade.WithPython,allerrorsareidentifiedatruntimeinsteadofshowingafailuretocompileerror.Thismakesiteasiertoidentifyandfixmistakesimmediately.

Thisisincrediblyusefulwhenyouwillbedesigningacomplexalgorithmwherechangesaremadecontinuously.Whereotherprogramminglanguageswillwastetimetakingyouthroughthecompile-run-debugcycle,Pythonsimplyshowstheresult(ortheproblem)inthesameinterpreter.

Hence,youcanmakeinnumerablechangestoapieceofcodeandexecuteitinreal-timeintheinterpreter.Thisbooststhelearningprocessasyoucanconsciouslymakeerrors,seeitsimpact,andtroubleshoottheprogram.Thisdramaticallyreducesthedevelopmentcycle,andbecomesespeciallyusefulforrapidprototypingofyourcode.

#5—PYTHONISOPEN

Pythonisanopenontwoaccounts:

1)Opensourceasprogramminglanguage

2)BuiltusingOpenobjects

Asanopensourceplatform,itsliberaldistributionlicenseallowsthelanguagetobeusedforcodingprograms/appsthatcanseamlesslybeintegratedasanextensionofotherproprietylanguages.

Intermsofcodingarchitecture,Pythonisgreatatintrospectionbecausethecodeisbasedondiscretechunksofprograms(knownasobjects).Wewillgettechnicallater,butforthemoment“beingopen”meansthatitwillbereallyhardforyoutowritedirtycodeorsidesteppropercodingmethodstosolveproblems.

Hence,Pythonforcesyoutowritebettercodefromthebeginning,andthisprovesveryhelpfulduringdebugging.

CHAPTER3.GETTINGSTARTED:PRE-REQS

ThereareonlytwoprerequisitesforgettingstartedwithinstallingandusingPython:

Reasonableknowledgeofusingacomputerandinternet.Acompellingdesireforlearninganewlanguageforcommunicatingwithcomputers.

INSTALLINGPYTHONONWINDOWS

DownloadthelatestversionofPythonfromtheofficialWebsite.[LINK]

NOTE:Twoversionsofthelanguageareavailable,Python2.xandPython3.xThedifference,inallitssimplicityisthatPython2.xislegacyi.e.itistheonethathasbeeninstalledonmostdevicesandhenceisthecurrentnormforPython,whereas,Python3.xisthepresentandfutureofthelanguage.

TheWindowsversionisdownloadedasanMSIpackage,andcanbeinstalledwithadouble-clickontheopenshellfile.

AllowthewizardtoinstallPythontothedefaultdirectory:

ForPython3.xitwillbeC:\Python3x\—(xbeingreplacedbytheversionyou’vedownloaded,thelatestbeing2.7)

NOTE:ThedifferentfoldersmeanthatyoucaninstallmultipleversionsofPythononthesamesystemwithoutcausinganyconflicts.

However,asingleinterpreteractsasthedefaultapplicationforPythonfiletypes.

That’sit.

YoucanusePython;however,itisrecommendedthatyouinstallthelibrariesandtoolsdescribednextbeforeworkingonwritingyourcode.Inparticular,Setuptoolsisamustinstallasitallowsyoutoeasilyuseotherthird-partyPythonlibraries.

SETUPTOOLS+PIPFromalltheSetuptools,thisisthemostcrucialthird-partyPythonsoftwarebecauseitextendsthecapabilitiesofthepackagingandinstallationfacilities(offeredinthedistutilspresentinthestandardlibrary).

OncetheSetuptoolsisaddedtoyourPythonsystemanddirectory,allPythoncompliantthird-partysoftwarecanbeaddedusingasinglecommand.Furthermore,withtheSetuptoolsinstalled,youcanaddanetworkinstallationcapabilitytothesoftwarethatyoucreate.

Python3,generally,comesequippedwithPIP.YoucandownloadthelatestversionoftheSetuptoolsforWindowsHERE.

NowinstallPIP,areplacementforthePythoncommandeasy_installandwhichintroducesun-installationofdifferentpackages.

VIRTUALENVIRONMENTSNext,youhavetoinstallaVirtualEnvironment,virtualenv,atooltokeepeachproject

self-containedandseparatefromoneanother.Thinkofitthisway:whenyouwriteacode,itleveragesthePythonworkenvironmenttoreduceitssize(e.g.usingsomepre-madefunctionsfromthePythonlibrary).Hence,whenitissaved,onlytheessentialinformationneededforthesavedfiletobereopenedandruninthePythonworkenvironment.

Nowyoucreateanothercodeandsaveit.

NowthenewprojectmayusedifferentlibraryobjectsfromPython,however,unlessamechanismexiststokeeptheirrelianceseparatefromoneanother,oneprogramcaneasilyconflictwiththeother.

Avirtualenvironmentseparatesalldependenciesrequiredbydifferentprojectsinseparateplaces.Hence,eachprogramcansafelyruninitsownsafehaven.

DownloaditfromHERE.

THESECONDPREREQUISITEAstrongdesiretolearnhowtowritecomputerprograms.

Ifyoudon’tknowhowtoprogramandarenewofPython,thenunderstandthataswithanynewlanguage,ittakestime,practice,andperseveranceinfaceofmistakesandsmallfailures.Hence,youmusthaveastrongdesiretolearnthelanguagetosucceed.

STRONGDESIRETOLEARNPythonrequiresfocusedeffortinlearningthebasics,learninganewmethodforlogicallybreakingdownaproblemintoconstituentparts,learninganewprogrammingmethodology(Pythonisanobjectorientedprogramminglanguage),andpracticingcodingbehaviorinanewcodingenvironment.

Don’texpectamiracletohappen.

Youwon’tlearnitbysimplyreachingtheendofthisbook.

Aswithanylanguage(spokenorcoded),practiceandexperiencematteralot.Simplyreadingandmemorizingsyntaxwillnotbringamiraculoustransformationandmakeyouanaptprogrammerinthefield.

Unlessyouarewilledbyatruedesiretolearnthenewlanguage,learningtoprogramcanbecomeboring,mistakeswillcompoundasade-motivatingfactor,andyouwillnotingrainanewanalyticprocessofbreakingdownproblemsandwritingsolutions.

PRACTICE,MOREPRACTICE,ANDEVENMOREPRACTICEAlllanguagesarelearnedbyrepetitionandexperimentation.

Youhavetolearnhowtoputtogetherphrasesandcreatemeaningfulsentencesoutofthem.WithPython,itisaboutusingthesyntaxandcommandstocreatechunksofcodethatcanperformanaction(takeinput,compute,displayanoutput,etc.),anddosoefficiently.

Thisbookwillofferyouthebasicsofthelanguage,butyoumustwillyourselftoputyourbraininhighgearandwriteALOTofcodefordifferentproblems.Onlythenwilltheinformationthatissharedinthisbookwillstickwithyou.

Thinkofthethingsyouhavebecomegoodatovertheyears:talking,surfing,gaming,playingmusic,generalknowledgeaboutfashion,writinggoodessays,humor,andmore.Allofthemneededtobepracticedagainandagaintogainsufficientcommandandconfidenceinyouabilities.

ProgrammingwithPythonisquitesimilartothatexperience.

CHAPTER4.VARIABLES,EXPRESSIONS,STATEMENT,STRINGS

RememberthoseEnglishgrammarlessons?How“eachsentence”ismadeofasubjectandanobject,hasnouns,pronouns,auxiliaryverbs,andadjectives,andthelike?

Justrememberhowwordsandauxiliaryverbswereusedtocreatesentences,andhowthesesentencesareusedtocommunicatemorecomplexthoughts.

Thisiswhatwearegoingtodohere.

Python(andmostotherprogramminglanguages)aremadeofsomeuniversalbasiccomponents.Theseinclude(inorderofincreasingcomplexity)variables,expressions,statements,andstrings.

Thenamesareself-explanatory.Let’sseethemindetail.

VARIABLE

Avariableisthe“x”youtriedtofindinmostofyourmathclasses.Inprogrammingitisadatatypecapableofcontainingchangeablevalues.

Theabilitytomanipulatevariableinaprogramminglanguageisoneofthemostpowerfulfeaturesinthecodingworld.

Hence,wemustbeginbyunderstanding“values”inPython.

VALUESANDDATATYPESValuesarecategorizedaccordingtothetypeofdatatheycanhandle.Forexample,“Hello,Programming!”,“2”,and“2.3”areallconsideredvaluesinPython,excepteachbelongstoadifferentcategoryordifferentdatatype.

NOTE:Datatypedonatesthedifferenttypesofdatathatcanbeusede.g.characters,numbers,floatpoint(decimalnumbers),etc.

Thenumeric2isanintegerbecauseitcontainsawholenumber,whereasthe“Hello,Programming!”isastringbecauseitcontainsastringofletters,and“2.3”isafloatbecauseithasdecimalnumber.YourPythoninterpreterisabletoidentifyandusestringsasasinglevalueenclosedwithinthequotationmarks.

Ifinconfusionaboutthetype,letPythontellyouthedatatypeofyourvaluewiththetype()command:

>>>type(“Hello,Programming!”)

<type‘str’>

>>>type(13)

<type‘int’>

Notethatthestringsarealwayscontainedwithinquotes“”.Hence,ifyouweretoputnumericvalueswithinthesequotes,theyautomaticallybecomestrings.

>>>type(“13”)

<type‘str’>

Furthermore,whenwritingstrings,avoidusingcommastoseparatetens,hundreds,andthousands.Forexample,ifyouwanttowritetwohundredthousandas2,00,000,Pythonwouldreactasfollows:>>>print(2,000,000)

200

Unexpectedright?

That’sbecausecommasareinterpretedbyPythonasseparators.Hence,youseethreevalues:2,0,and0.

NOTE:Thesyntaxforprintisprint(x)with‘x’beingreplacedbystrings(“string”)ornormalnumericvalue(2)

ThisisdifferentfromPython2,wherethesyntaxissimply:printx,print2,orprint“this”

Othertypesincludefloat(fordecimalplaces)

>>>type(13.1)

<type‘float’>

>>>type(“13.1”)

<type‘str’>

NOTE:Youcanuseboth,single(‘’)anddouble(“”)quotesforwritingstringsinPython.AND,youcanusedoublequoteswithinsinglequotes.Forexample:(‘Hesaid,“Loandbehold!”‘)

Let’sstartwithvariables.

VARIABLESRememberhowbasicequationswerecreatedinmath?

Question:IfSamboughttwoeBooksfor$3,howmuchwillitcosttopurchase5eBooks?Wenormallybeganwithsupposing“x”asthecostof5eBooks.

Oncesupposed,“x”canbeusedanywhereinthesolutionandanyonecaneasilyfigure(interpret)that“x”isreferringtothe“Costof5eBooks”definedinthebeginning.

Inprogramming,avariableisthenamethatreferstoachangeablevalue—onethatcanbechangedandautomaticallyupdatedatwill.

Likemath,variableshavetobedeclared/created(supposed)andthenassignedavalue.Inpython,thevalueofavariableisassignedusingtheassignmentstatement:>>>message=“I’mprogrammingwithPython!”

>>>x=2015

>>>yr=365.25

Noticehoweachtypeofdataisassignedinasimilarmanner,startingwithastring,aninteger,andafloatingpointnumber.Themostimportantthingistheequalsign“=”thatseparatesthenameofthevariable(lefthandside)fromthevalueofthevariable(righthandside).Theequalsign“=”isknownastheassignmentoperator.

Theleft-hand,right-handdivideisarule.Deviationisnotpermitted.Ifyoureversetheorder,itbecomesmeaninglessfortheinterpreter.

Hence,thefollowingmakesnosense.>>>“I’mprogrammingwithPython!”=message

>>>2015=x

>>>365.25=yr

TYPESOFVARIABLESVariablesalsohavetypes.Intheexampleabove,the message isastring, ‘x’ isaninteger,and ‘yr’ isafloat.

Youcanverifythetypeofthevariableusing type().>>>type(message)

<type‘str’>

>>>type(x)

<type‘int’>

>>>type(yr)

<type‘float’>

Notehowthetypeofthevariablecorrespondstothetypeofthevalueitcontains.

NAMINGYOURVARIABLES,THEILLEGALITIESCertainnamingconventionsareusedwhennamingvariables.Thesearesimplystandardsthatareusedtostandardizehowcodeiswrittenandtokeepitclean.Thisgainsimportanceasyourcodegetslongerandyourvariablesbecomemoredescriptive.

Additionally,certainpythonruleslimithowyourvariablecanbeassigned.Yourvariablemust:

1. Alwaysbeginwithanalphabet/letter2. Neveruseillegalcharacters($,&,*,etc.)3. NeveruseaPythonkeyword

Therefore,thefollowingwillresultinsyntaxerrors:>>>14numbers=“Whatarethosefourteennumbers?”

SyntaxError:invalidsyntax

>>>Increase$=985

SyntaxError:invalidsyntax

>>>class=“PythonBasics“

SyntaxError:invalidsyntax

Now “class” isaPythonkeyword,whichmeansitispartofitsrulesandstructure.

Pythonhasthirty-onesuchkeywords:

raise while return try with print

is or lambda not pass

for if from global import

del except elif else exec

as class assert break continue

yield and def finally in

Keepthistablehandy,andiftheinterpretercomplainsaboutsyntaxerror,checkyourvariablenaming!

STATEMENTS

Likenormallanguage,astatementisaninstruction.InPython,youcanexecuteprimarilytwokindsofstatements:print and assignment .Theformerproducesavaluewhilethelaterdoesnothing.

Whenyouwriteastatement,theinterpreterexecutesitandtriestodisplayresults:print(3)

t=17

print(t)

Theabovecodewillproducetheoutput:3

17

Theassignmentstatementusedforcreatingavariableproducesnooutput.

EXPRESSIONSAsinlanguage,anexpressionisacompletethought,withapremiseandaconclusion.Inpython,anexpressionhasinputs,adefined/expecteduseofthoseinputs,andanexpectedwayofeitherdirectlydisplayinganoutputorcomputingittodisplayanoutput.

Generally,meaningfulexpressionsareacombinationofvariables,values,statements,andoperatorsthatforcestheinterpretertoevaluateitanddisplayresults:>>>1+1

2

AvalueandavariableitselfaresimpleexpressionsinPython:>>>2015

2015

>>>t

17

However,theseexpressionssimplyprint/displaytheexpression.Evaluatinganexpressionisnotsimilartosimplyprintingavalue.

Taketheexample:>>>message=“Writingexpressions?”

>>>message

“Writingexpressions?”

Noticehowthequotationmarksaredisplayedintheoutput.However,whenusing print() ,onlythecontentsofthestringaredisplayed:>>>print(message)

Writingexpressions?

Thisisbecausethe print() statementfetchesthevalueofthevariable(thestring).

Now,anexpressionallbyitselfisalegalstatement.Youcanwriteasmanyasyouwant,butunlessyouusecertainoperatorsandcommandstocommunicatethepurposeoftheexpression,NOOUTPUTwillbedisplayed.Forinstance:2015

365.25

“Python,Expressions!”

13+1

Nooutputwillbedisplayed.

Thisiswhereoperatorsandoperandscomeintoplay.

OPERATORSANDOPERANDSAcodeissupposedtoperformcertaincomputationsontheexpressionstogeneratepredictableoutputs.Computationsareperformedusingoperators—specialsymbols

whichyoumaythinkofasshortformsfordifferentcommands.

Thevaluethattheoperatorusesiscalledanoperand.Herearesomeexamples:

1+2+3

t-20

t*30+minutes

t/60

(1+2+3)*(6-2)

Howthesymbolshavebeenused+,-,/,*(formultiplication)arethesamewaytheyareusedinmathematics.Now,whenavariableisusedwithoperator(s)tocreateanexpression,theinterpreterfetchesandcomputesthevalueassignedtothatvariable.

However,thereisacaveat.Thoughaddition,multiplication,subtraction,andexponentiation(representedbythedoubleasteriskoperator**)haveasingleuseandgenerateanexpectedresult,divisiondoesnot.

Let’ssaythefollowingexpressionisused:>>>t=49

>>>t/60

0.8166

Butwhatifwantedtoperformanintegerdivisionwheretheanswerisalwaysroundedofftotheclosestintegervalue?

Let’ssay:>>>t=121

Thisiswhere“//”isusedtoindicateourintention>>>t/60

>>>t//60

2.0166

2

Anotherwayofovercomingistoassigndatatypestotheanswer(afloat),butwewillcometothatlater.

ORDEROFOPERATIONSYoucanusemultipleoperatorsinasingleexpression;howevertheirevaluationisdependedontherulesofprecedence.

Pythonfollowsthesameruleasisappliedformathematicaloperators.RememberPEMDAS tomemorizetheorder :

Parentheses—Expressionsintheparenthesisarealwaysevaluatedfirst.Hence, 3*(4-1) is9.Parenthesisarealsoagreatwayformakingiteasiertoread

theexpressionsuchas (t*100)/60 .Exponentiation—(**)hasthenexthighestprecedence.Hence, 3**1+1 is4andnot9,whereas 4*1**3 is4andnot64.MultiplicationandDivision—Bothhavethesameprecedence,albeithigherthanadditionandsubtractionAdditionandSubtraction—Alsohavethesameprecedence,albeitlowerthanmultiplicationanddivision.

Whatifmultiplicationanddivisioncomeinthesameexpression?

Forexample: t*100/60

Operatorsthathavethesameprecedenceareevaluatedfromtheirappearancefromlefttoright.Hence,intheexpression t*100/60 ,multiplicationhappensfirst,followedbydivision.

OPERATIONSANDSTRINGSGenerally,youcannotperformanymathematicaloperationsonstrings.Thisincludesinstanceswherethestringslooklikenumbers,oronlyhavenumbersinthem.Thefollowingexampleshowsanillegalmathematicaloperationonasetofstrings:

message-1“Word”/2015message*“Now”“2012”+3

Thoughmathematicaloperationscannotbeperformedalgebraically(orasweareaccustomedto)onstrings,someoperatorscanworkwiththem,butinadifferentmanner.

Forexample,the“+”operatorwhenusedwithstringsperformsconcatenationinsteadofaddition.Itmeansthatthetwostrings(oroperands)arelinkedend-to-endi.e.theyareattachedoneaftertheother:

Subject=“Python”

Object=“ProgrammingLanguage”

Aux_Verb=“isa”

Adj=“simple”

print(Subject+Aux_Verb+Adj+Object)

Theoutputofthiscodewillbeprogram PythonisasimpleProgrammingLanguage .Thespacesbeforethewordsinthestringarepartofstring,andnecessarytoproducethegrammaticallycorrectspacingbetweentheconcatenatedstrings.

Themultiplicationoperator(*)alsoworksonstrings.Itsfunctionistoperformrepetitionsonthatstring.So,forexample,theoperations:

‘Why?’*3

Willproducetheresults‘Why?Why?Why?’

Inmultiplication’s(*)case,oneoftheoperandsmustbeanintegerwhiletheotherastring.

CHAPTER5.FUNCTIONS

Let’sdelveintopurposefulprogrammingwheretheprogramwilldemanduserinputtoexecuteacommandortoperformatask.

Thisisachievedusingfunctions.

Let’stakeareallifeexamplesayyouwanttosurpriseafriendontheirbirthday.Youinformotherfriends,gatheragroup,andtellthemhowthepartywillgo.Forexample,youdecideonasignalatwhichtheywillturnonthelights,blowthetrumpets,orsingthebirthdaysong.Inthisscenario,youhavecreatedabasicplanofactionandasignal(aninput)andhoweveryone(individually)willreacttoit.

Youarenotexpectingtotelleveryonewhattodoagainwhenyougivethemthesignal,BECAUSEyouhavealreadydefineddifferentfunctionsandassociatedsignalsthatwillactivatethem.

InPython,functionsaresmallerindependentpiecesofcodeinyourprogram.Theyallowyoutodivideandorderyourcode,andhencemakeitcompact,moreorganized,andreadable.Oncecreated,afunctioncanbeusedatanytime,andanynumberoftimesanywhereinyourprogram.

USINGAFUNCTIONPythonhasalibraryfullofpre-madefunctionsforvariouscommontasks.Youcanusethembysimplycallingthem,andgivingthemaninput.

“Calling”afunctionsimplymeansusingthefunctionname(andnotcopyingthewholecodeagain),andgivingthefunctionaninputitcancompute.

Thinkofitlikecallingthemoversortheletterman.Theyknowtheirfunction,andifyougivethemtherightinput(i.e.thingstobemovedoraletter/parcel),thenyouwouldnothavetoexplainittothemwhattodowiththatinput.Theywillcompletethejobonceyougivethemtherightinput.

InPython,callingafunctionissimple.Defineaparameternameanditsworkingparameters:

function_name(parameters)

Simple,right?

Let’sunderstandthedetailsofthesyntaxshownabove:

Function_Nameidentifieswhichfunctionitisyouwanttouse.Youwillfigureitoutyourself,asinthepreviousanalogy,ifyouwanttomovesomethingyou’dcallthemoversandalettermanifit’sasmallparcel/letter.Asanexample,abasicfunctionistheraw_inputfunction.We’lluseitsoon.Parametersarethevaluesortheinputsthatyoupasstothefunction.Thisvaluewillinformthefunctionwhatandhowitshoulduseit.Forexample,ifyouhaveafunctionthat addedavaluetoanumberaftermultiplyingitby3thentheparameterswillbe1)thenumberitshouldmultiplyby3,and2)thenumberitshouldaddtothisresult.Soifyouput5and2intheparametersforthisfunctionthenitwillfirstmultiply(5x3)andthenadd2(15+2),givingyou17

PARAMETERSANDRETURNEDVALUESNow,functionsnormallyworkinthebackgroundandwillnormallynotshowtheresultofthecomputationtheyhaveperformedontheparametersyouhavegiventhem.

Returningthevalueorresultofitscomputationisimportanttoknowwheretheprogramis,orifitisgeneratingtheexpectedresults.Whatifyouhavegivenitaletteroranillegalsymbol($,%,#)insteadofanumber?

Sohowdoesafunctionshowwhatitdoes,orhasdoneontheterminal?

Let’sseehowthecomputerseesthefunction.Itdoesnotseethenameofthefunction(orincaseofavariable,thevariable’sname),rather,itonlyseesthefinalvaluethatthefunctionorthevariablehasstoredinit.

Hence,incaseofthefunction,thecomputerseesthefinal,endresult.

Let’staketheexampleofafunctionmultiply() thatmultipliesanynumberby7.So,itsinputisanynumberyoucanthinkofandplaceitinthebrackets,thefunctionmultipliesit

by7.

NOTE:multiply()isnotapre-madefunctioninPython.Youcan’tuseitstraightoutasmentionedhere.

Soifyoutypedthis:

t=multiply(60)

Itwillappeartothecomputerasthis:

t=420

Thefunctionranitself,andreturnedanumbertothemainprogram,usingtheparameterswehadgiven.

Let’stryarealfunction,input .

NOTE:PreviousversionsofPython(<Python3)usedraw_inputinstead.

Thefollowingfunctionaskstheusertoenteravaluethatitturnsintoastringoftext.Forexample:

#thefirstlinemakes“t”equaltothevaluethatyoutypeinonthescreen

t=input(“Typesomething,andIshalldisplayitonthescreenagain:”)

#Thenextlinewillprint,orreturnthevaluethatyouhaveenteredin‘t’.Itwillshowtheresultofthefunction

print(t)

Theresultissimplythecontentthatyouhaveenteredonthescreenaftertheprogramisrun.

NOTE:‘#’isusedforwritingcommentsinthecode.Anylinethatbeginswith“#”isnotcomputedbythePythoninterpreter.

Thinkofcommentingasyourin-programdocumentation,informingorremindingyouaboutwhateachchunkofcode/functiondoes.

Itbecomescrucialasyourcodebecomeslargerandmorecomplex.Practiceitfromthebeginning .

So,ifyoutypein“Really?”intheaboveprogramwhenaskedtodoso,thecomputerseesthefunctionas:

t=“Really?”

print(“Really?”)

Remember,thattothecomputer,variableisjustastoredvalue.Itdoesnotappearas‘t’.Soisthecasewithfunctions.Theydon’tappearasthewholecode,onlythevaluetheycontaininthem.

DEFININGYOUROWNFUNCTIONSYoucancreateyourownfunctionsusingthe‘ def ’operator.

Thinkofafunction,andwhatitwilldo.Nownameit,anduse‘ def ’asfollows:

deffunction_name(parameter_1,parameter_2):

#noticethecolon“:”attheendoftheline?#itisanimportantpartofthesyntax.Always#additattheendoflinethatstartswith#‘def’

{thisisthecodeinthefunction}

{morecode}

return{valuetoreturntothemainprogram}

Recallthattothecomputer,thevariableinthefunctionlookslikethevaluethatisstoredinsideitandthatfunctionsaresimilarandonlythevaluethattheyreturnisseenbythecomputer.

Itdoesnotmatterhowlargeyourfunction’scodeis.Onlythevaluematters.Becausethefunctionisaseparate,self-containedprogram,itdoesn’tseeanyofthevariablesinyourmainprogram.

Whythestressonwhatthecomputersees?

Hereisanexampletoshowtheimportance.Thefollowingfunction‘written()’willprinttheword“Functionsareindependentofthemainprogram”onthescreen,followedbyreturninganumber“54321”tothemainprogram.

#creatingthefunction

defwritten():

print(”Functionsareindependentofthemainprogram“)

return54321

#howtousethefunction

written()

Thelastlineofcodeiscallingthefunction.Whenyoutypethat,thefunction’svaluesaredisplayedonthescreenandnotthecompletefunction:

Functionsareindependentofthemainprogram

54321

Sowhathappened?

Assoonasthe defwritten() wasrun,Pythoncreatedafunctionandlabeledit‘written’

Whenthewritten() wasrun,Pythonexecutedthefunction‘written’thatithadpreviouslycreated.Runningthefunctionmeantexecutingalllinesofcodewithinin.

Thefunctionfirstprinted“Functionsareindependentofthemainprogram” andthenreturnedthenumber‘ 54321 ‘backtothemainprogram.

Asaresult,themainprogramonlyseesthelineas‘print54321’andsodisplays‘54321’inthenextline.Yourfunctiondidnotknowthatthestring “Functionsareindependentofthemainprogram” hadbeenprintedalready,allitsawwasthatitreceivedanewvalue‘54321’andprintedthatonscreen.

Functionscanalsoreceiveargumentsi.e.youcanpassvariablestothem.Forexample:

defa_function_with_args(username,message):

print(“Welcome,%s,Iamyournewfunction.Iwishyou%s”%(username,message))

Functionscanalsoreturnvalues.

Functionsmayreturnavaluetothecaller,usingthekeyword—‘return’asusedinthepreviousexample.Anotherexample:

defadd_both_numbers(a,b):

returna+b

CHAPTER6.CONDITIONALS,FLOWCONTROL,DECISIONS

Usefulprogramsareabletomakedecisionsbasedontheinputs.Thisisachievedbygivingthemtheabilitytochangethebehaviororflowoftheprogrambasedontheinputs.Thisisdoneusingconditionalstatements.

Theflowofthecodeistheorderofthecodeyouhavewritten.Recallthebirthdayexample.Youmayhaveplannedthatthehallwaylightswillgoupfirst,followedbythefriendsonthestairwayssingingthesongs,someonecomingwiththecake,etc.

Butdifferentinputs(orreactionsbyyourfriends)theflowofthepartymighthavetochange.

Incoding,normally,whenthecodeisexecuted,theinterpreterreadsitlinebyline,movingfromthetoptothebottom.However,attimesyoumayneedtoexecuteafunctionthatbegins40linesahead.Themosteffectivewayofincreasingefficiencyoftheprogramistobreaktheflowandimmediatelybringtheinterpretertothefunctionandexecuteit.

Whenthereisaneedtobreakthecodeandexecuteadifferentblockofcodealtogethertocompleteatask,conditionalscomein.

ConditionalscanbedividedintobasicconditionsandtheIfconditions,including:

If-StatementIf-ElseStatement

Let’stakethemonebyone.

BASICCONDITIONSTheseincludeallthearithmeticcomparisons,suchaslessthan(<),greaterthan(>),equal(=).Forexample:

3<4

3>2

t=5

t>7

AlloftheabovehaveBooleanresultsi.e.theyareeithertrueorfalse.Theseconditionscanbeusedtocontroltheflowoftheprogramusingconditionalstatements.

However,notallarithmeticdecisionaretransferredexactlytoPython:

Greaterthan > >

Lessthan < <

Greaterthanorequal ≥ >=

Lessthanorequal ≤ <=

Equals = ==

Notequal ≠ !=

CONTROLFLOWWITHTHEIF-STATEMENTWearewritingacodeforamovingcompanythatoffersflatratesforallitemslessthan60kg,whereasanythinggreaterthanthatischarged$20extra.Ourcodewillusedwiththeirweighingmachinetoinformthecustomeroftheextracharges.Here’sanexamplecode:

weight=float(input(“Pleaseentertheweightofyourluggage(inKg):”))

ifweight>60:

print(“Thisexceedsour60Kgflat-ratelimit.Anadditional$20isappliedforheavierluggagelikethis.”)

print(“Thankyouforyourbusiness.”)

Noticetheindentationbeforethefirst print command.ThisindentationtellsPythonwhattodowhenthestatementweigh>60istrueorfalse:

Whentheweightisgreaterthan60kg,itprintsadditionalcharges,andWhenitisnottrue(weight<60),itthanksthecustomer.

Thesyntaxfortheif-statementis:

ifcondition:

Indentedcode/statement

#thecolonispartofthesyntax.

Whatifyouwanttoexecuteseparatecodesforboth,TrueandFalseconditions?If-elsestatementisusedforthataswellusingtheif-elsestatement.

CONTROLFLOWWITHIF-ELSESTATEMENTThegeneralsyntaxforif-elsestatementsinPythonis:

ifcondition:

IndentedcodeifconditionisTrue

else:

IndentedcodeifconditionisFalse

Theindentedblockscanhaveanynumberoffurtherstatementsinsidethem.Forexample:

time=float(input(‘Howlongdidyourun?’))

iftime>20:

print(‘Goodwork!Let’scontinuemaintainingourhealth’)

else:

print(‘Goodeffort.Let’strytohitourtargettomorrow!’)

print(‘ExerciseforHealthyLiving’)

Theif-elsestatementislimitedtotestingasingleconditionandcontroltheflowusingonlytworesults(True/False).Multipletestscanbeincludedusingthe if-elifstatement .

CONTROLLINGFLOWUSINGIF-ELIFSTATEMENTSWhynotusetheif-elsestatementrepeatedlyincaseofmultipletests?Let’staketheexampleofgradeassigner:defGradeAssign(score):

ifscore>=85:

assign=‘A’

else:#ifnotAthenmaybeB,C,DorF?

ifscore>=75:

assign=‘B’

else:#ifnotAthenmaybeC,DorF?

ifscore>=65:

assign=‘C’

else:#grademustDorF

ifscore>=60:

assign=‘D’

else:

assign=‘F’

returnassign

Noticethenumberofindentations.

Asyourcodegrowslonger,thiswillbecomeproblematic.Seehowif-eliftransformsit:defGradeAssign(score):

ifscore>=85:

letter=‘A’

elifscore>=75:

letter=‘B’

elifscore>=65:

letter=‘C’

elifscore>=60:

letter=‘D’

else:

letter=‘F’

returnletter

NESTEDSTATEMENTSYourcodecanhavestatementswithinstatementsaswell:

ift>60:

Indentedstatement#1

else:

ift<30:

Anotherindentedstatement#2

else:

Indentedstatement#3

Asyourprogramgrows,nestingstatementswillincreasethedecision-makingabilityofyourcode.

CHAPTER7.ITERATIONS

Programsareusedtoautomateandsimplifyproblems.Thisrequiresrepeatingtasks,e.g.askingforinputmultipletimeswhenatableneedstobefilled.Thisiscalledaniterationofthesametask.Theyrequiretheinterpretertoexecutethesameblockofcodemultipletimes.

However,thisisnotpossiblewithhowtheinterpreternormallyworksi.e.sequentiallybymovingfromoneblockofcodetothenext.

Thisiswhereloopstatementscomeintoplay.

Theyallowustoexecutethesameblockofcodeasmanyasisneededtocompletethetask.

Therearetwomainloops:the WhileLoop andthe ForLoop .

Bothloopsrelyonupdatingvariables.Sofarwehaveonlycreatedandusedvariables,withoutchangingandupdatingtheoriginalvalueofthevariableduringexecution.Here’sanexampleofupdatingvariables:

a=1

b=a+2

b=2*b

a=b-a

print(a,b)

Theprogramisexecutedstep-by-step,toptobottom.Here’showthevariablesgetupdatedateachline:

Line Valueof‘a’

Valueof‘b’ Details

1 1 -

2 1 3 a=1,soa+2=1+2=3

3 1 6 b=2*b.Nowb=3,so2*b=2x3=6

4 5 6 b-a=6-1=5

5 5 6 print:56

Theinterpreteralwaysexecutesthecommandsinasequentialorder,updatinganyvariablesthatarechangedduringtheprocess.

Theloopstatementsbreakthissequentialflow,allowingustoaccessfunctionsdefinedanywhereinthewholecode.

LoopControlStatements

Whenshouldtheloopstart?Howlongshoulditcontinue,andwhenshoulditterminate?

Thisisachievedusingloopcontrolstatements.

Withoutthem,theinterpreterwilleithernotexecutethelooporifitdoeswillnevergetoutofit.Let’sseehowitworkspractically.

ListTypesandRangeFunctions

Tousethefor-loop,itisimportanttounderstandlisttype.Listsareorderedsequenceofdata.Someexamplesinclude:

[‘white’,‘red’,‘green’]

[1,2,3,4,5,6]

[‘word’,34,‘anotherword’,-4,‘last’]

[]#completelyemptylist

Thebasicfor-loopreliesonthelisttype.

THEFOR-LOOPThisloopiterates(repeats)afunctionorsetofcommandsforthefixednumberofparametersyougiveit.ThisisdifferentfromtheWhile-Loop,whichrunsaslongasaconditionistrue.

Forexample:

Ifitisrainingoutside,taketheraincoat.Whilethesunshines,themonkscontinueworkingtirelesslyonthefield

Hence,unlikethewhile-loop,thefor-looprunsonce.

Thesyntaxoftheforloopis

forvariable/functioninsequence/list:

indentedstatementstoloop

Here’sanexample:

forcountin[1,2,3]:

print(count)

print(‘Go’*count)

Theabovefor-loophasthefor-statement,thevariablewhichithastoworkon,andthelistofparametersithastoworkwith.

Theloophasthreeparametersandavariable.Whenitisexecuted,thetwolinesofcode

arerepeatedthreetimes,onceforeachlistparameter.

Line Valuein‘count’ Details

1 1 Takesfirstelementfromlist

2 1 print1

3 1 Applyoperator‘Go*1equal‘Go’;printsGo

1 2 Updatevaluetonextelement

2 2 print2

3 2 ‘Go*2equals‘GoGo’;printsGoGo;

1 3 changecounttothenextelementinthelist

2 3 print3

3 3 ‘Go’*3is‘GoGoGo’;printsGoGoGo;

Listcomplete,done.

Inthiscase,thefor-loopperformstwoactions:updatingthevariableinplaceof‘item’,andrunningtheindentedblockofcodeafter.Theaboveexampleusedthevariablewithintheloopaswell.

Asimplerloopcanalsobecreatedwithoutusingalist.ThisiswhereRange(apre-madefunctioninPython)canbeused.

forxinrange(7):

print(‘For-Loop’)

Noticethatthevariablexisnotusedinsidethebodyofthefor-loop.Youcanchoosethenumberoftimestheloopmustiterateorrepeatitself.

#aprogramforspecifiedrepetitions

n=int(input(‘Howmanytimesdoyouwanttorepeatthis?:‘))

forxinrange(n):

print(‘Repeating…’)

Onexecution,theprogramwillprintthestatement‘Repeating…’nnumberoftimesi.e.thenumberyouenterinthebeginning.

THEWHILELOOPItisaBooleanloopthatrepeatsthesamesetofcommanduntiltheoriginalconditionisFalse.

ThesyntaxforthewhileloopinPythonprogramminglanguageis:

whileexpression:

indentedstatement(s)

Aslongastheexpression(itsBooleancondition)holdstrue,theindentedblockofcodewillbeexecutedagainandagain.Themomenttheconditionbecomesfalse,theprogrammovesouttheloopandexecutesthenextlineoutsideofit.

Example

n=0

while(n<5):

print(‘Ihavecountedtill:‘,n)

n=n+1

print(“Goodbye!”)

Theabovewhile-loopholdstrueforaslongastheupdated‘n’hasavaluelessthan5.Themomentitreaches5theprogramwillmovetothefirstlineoutsideoftheloop(theun-indentedline).

Goodbye!

Howaboutaloopthatcanneverend?

Aninfiniteloopwherethefalseconditiondoesnotexist?Theseloopsareimportantforkeepingtheprogramrunningandseekingcontinuousinputfromtheuser.Ifaninfiniteloopwasnotrunning,anysmartdeviceorPCwouldshutdownafterloading(completingloading)itsoperatingsystem.

AloopbecomesinfiniteloopifaconditionneverbecomesFALSE.

n=1

whilen==1:#Thisistheofficialsecretforconstructinganinfiniteloop

a=input(“Enteravalue:”)

print(“Youentered:“,a)

print“Goodbye!”

CHAPTER8.LISTS,DICTIONARIES,TUPLES

Variablesallowustostoreinformationthatcanbechangedanytime.However,theystoreasinglepieceofinformationatatime:avalue,astring,etc.

Whatifweneedtostorealistofinformationthatwillnotchangeovertime?

Forexample,thecontactinformationofyourfamilymembers,thenamesofthemonthsoftheyear,oraphonebookwhereyouhavemultipleinformation(thenameofthecontactandrelatedphonenumbers.

ThisiswhereLists,Tuples,andDictionariescomein.Let’sbrieflydiscusseachsoyouknowthedifference,beforeusingtheminacode.

List

Asthenameimplies,itisalistofvalues.Thevaluesinalistarecountedfromzeroonwards(thefirstvalueisnumberedzero,thesecond1st,andsoon).Listletsvaluestoberemovedandaddedatwill.

Tuples

Theyaresimilartolistsexcepttheirvaluescannotbemodified.Oncecreated,thevaluesremainstaticfortherestoftheprogram.Again,thevaluesarenumberedforreference,startingwithzero.

Dictionaries

Likeanormaldictionary,itallowsyoutocreateanindexofwordswhereeachwordhasauniquedefinition.InPython,thewordiscalledthe‘key’whereasitsdefinitioniscalledits‘value’.Likeadictionary,noneofthewords/keysarenumbered.Thevaluesinthedictionarycanbecreated,removed,andmodified.

Let’sstartwiththeunchangingtuples.

USINGTUPLESTuplesareeasytocreate.Nameyourtupleandlistthevaluesthatitwillcarry.Here’satupleforcarryingthemonthsoftheyear:

months=(‘Jan’,‘Feb,‘Mar’,‘Apr’,\‘May’,’Jun’,‘Jul’,‘Aug,‘Sept,‘Oct,\‘Nov,’‘Dec’)

Syntactically,atupleisacomma-separatedsequenceofvalues.Theparenthesisandthespaceafterthecommaaresimplyaconvention,andnotnecessaryforcreatingatuple.Furthermore,noticethe‘\’attheendofeachline?Itcarriesthelinetothenextline,makingbiglinesmorereadable.

Oncecreated,Pythoncreatesanumberedindextoorganizethevaluesinatuple.Startingfromzero,thevaluesareindexedintheorderyouenteredtheminthetuple.Theabovetuplebecomes:

Index Value

0 January

1 Feb

2 Mar

3 Apr

4 May

5 Jun

6 Jul

7 Aug

8 Sep

9 Oct

10 Nov

11 Dec

Soifyouweretocallthetuple‘month’,youwillusetheindextocallit:

>>>month[2]

Mar

Additionally,Pythonhasaverypowerfultupleassignmentfeaturethatallowsustoassignvaluetovariablesontheleftwithvaluesontheright.Hence,forthe‘months’wehavecreatedearlier,wecanfurtherassignvaluestoeachofthevalueinthelist:

>>>(research,submitoutline,discussion,study,seminars,presentation,fieldtrip,submitpaper,paneldiscussion,finalpresentation,semesterends)=months

Theonlyrequirementisthatthenumberofvariablesontheleftmustequalthenumberofelementsdeclaredinthetuple.

Asimplewayoflookingatthisassignmentistotothinkofitastuplepacking/unpacking.Whenpacked,thevaluesontheleftarepackedtogether:

>>> months=(‘Jan’,‘Feb,‘Mar’,‘Apr’,\‘May’,’Jun’,‘Jul’,‘Aug,‘Sept,‘Oct,\‘Nov,’‘Dec’)

Intupleunpacking,thevaluesontheright(thenamesofthemonths)areunpackedintovariables/names/categoriesontheright:

>>> months=(‘Jan’,‘Feb,‘Mar’,‘Apr’,\‘May’,’Jun’,‘Jul’,‘Aug,‘Sept,‘Oct,\‘Nov,’‘Dec’)

>>>(research,submitoutline,discussion,study,seminars,presentation,fieldtrip,submitpaper,paneldiscussion,finalpresentation,semesterends)=months

>>>research

Jan

>>>seminars

May

>>>submitoutline

Feb

Anotherpowerfuluseoftupleiswhenyouhavetoswapthevaluesoftwovariables.Normally,youwouldhavetouseatemporaryvariableforswapping:

#Swap‘b’with‘a’

temp=b

b=a

a=temp

Atupleresolvesthisinasingleline:

(b,a)=(a,b)

Simple.Therighthandsideisatupleofvalueswhilethelefthandsideisatupleofvariables.Naturally,thenumberofvaluesmuchalwaysmatchesthenumberofvariables:

>>>(a,b,c,d)=(4,3,2)

ValueError:needmorethan3valuestounpack

USINGLISTSListsaresimilartotuples:theystorearangeofvaluesandaredefinedinasimilarfashion.However,unliketuples,youcanmodifythem.Thismakesthemthenormalchoicewhenitcomestostoringlists.Here’sanexampleofalist:

team=[‘Sam’,‘Michel’,‘Azazel’,‘Harrison’]

Noticethattheonlydifferenceinsyntaxistheuseofsquarebracketsinsteadofparentheses.Liketuples,thespacesafterthecommaareastandardpracticeforincreasingreadability.

Recallingthevaluesstoredinthelistarealsosimilartocallingvaluesinatuple:

printteam[3]

Harrison

Liketuples,youcanalsocallvaluesfromarangewithinthelist.Forexample,team[1:3]willrecall3rdand4thmembersoftheteam.

Theimportantthingwithlistsisitsabilitytoallowchange.Thisiscrucialwhenyouarebuildingdatabasesthatstorevalues(e.g.agrocerystore’sinventorywillhavechangingvaluesofthestockandneedtobeupdatedregularly).

Let’ssayyouinductanothermemberintoyourteam,howwillyouaddhim/her?

Valuescanbeaddedusingthe ‘append() ‘function.Thesyntaxoftheappendfunctionisoftheform:

list_name.append(value-to-add)

Hence,foranewmember,Gabriel:

team.append(‘Gabriel’)

Anddone!Thenewmember’snameisaddedafterthelastvaluestoredinthelist(‘Harrison’).

Howdoyouremoveanitemfromalist?SupposeMichelisnotgettingalongwithAzazelandGabriel,andisloweringthemoraloftheteam,etc.

Todeleteavaluefromthelist,youuse‘del’.RecallhowPythonindexesthelists,beginningfromzeroandonwards.SoMichelisthesecondvalueonthelist,makingitsindexnumbering‘1’.

#RemovingMichelfromthelist

team=[‘Sam’,‘Michel’,‘Azazel’,‘Harrison’,Gabriel]

delteam[1]

Youcandeletearangefromthelistbyassigninganemptylisttothem:

team[1:3]=[]

Nowtheteamthelastthreenamesremovedfromit.

WhatifyouwantedtoaddanewteammemberrightafterMichel?Normally,append[]addsthenewvalueattheendofthelist.

Yousimplytellafterwhichmemberthenewmembershouldbeplaced.Thisiscalledslicingthelist:

>>>team=[‘Sam’,‘Michel’,‘Azazel’,‘Harrison’]

>>>team[1:1]=[‘Gabriel’]

team=[‘Sam’,‘Michel’,‘Gabriel’,‘Azazel’,‘Harrison’]

METHODSTHATCANBEUSEDWITHLISTS.appendisjustoneoftheseveralmethodsthatareextensivelyusedwithcreatinglists.Othermethodsincludethefollowing:

.insertitisusedforpostinganewentryatthespecifiedindexnumber.Forexample,wanttoaddnumberstoyourlistofteam:>>team.insert(1,3320)

Thisinsertsthenumber3320atposition1,shiftingtheothervaluesupi.e.2ndbecomes3rdandsoon.

Ifyouwanttorepeatthelistwithinitself,thenyouwillsimplyuse .extend init.>>>team.extend([‘Sam’,‘Michel’,‘Azazel’,‘Harrison’])

>>>mylist

[‘Sam’,‘Michel’,‘Azazel’,‘Harrison’,‘Sam’,‘Michel’,‘Azazel’,‘Harrison’]

Ifyouwanttofindtheindexnumberofanyvalueinthelistuse .index

>>>team.index(3)

‘Harrison’

Reversethewholelistusing .reverse

>>>team.reverse()

[‘Harrison’,‘Azazel’,‘Michel’,‘Sam’]

Removethearepetitiveitemorthefirstuseofanyitemusing .remove

>>>team.remove(‘Sam’)

[‘Michel’,‘Azazel’,‘Harrison’]

Orincaseyouhaveanumberlist,andyouwanttosorttheminascendingorder,use .sort

>>>numlist.sort()

[1,3,3,3,7,9,10,10,24]

USINGDICTIONARIES

Previouslywehavecreatedlistsofnamesofateamandatuplewithvariableandvalueassignment.However,inbothofthem,thevalueoftheindexedvariablecanonlybecalledbygivingtheindexnumberforthatvalue.

Whatifyouwanttocreateadatabase,orasmallphonebook,thatgivesyouthedetailsofavariablewhenyouenteritsnameinsteadoftheindexnumber?Listsandtuplescannotgiveyoutherequiredaccessibility.

Dictionariescan.

Recallthatdictionarieshavekeysandvalues.Inaphonebook,youhavenamesofthepeopleandtheircontactdetails.Seeanysimilarities?

Creatingadictionaryissimilartomakingalistoratuple,exceptaslightdifferenceinitsbrackets.

(Tuples)useparenthesis[Lists]usesquarebrackets{Dictionaries}usecurlybraces.

Here’sanexampleofadatabaseformoneyowedtoeachmemberyourbusinessteam:

#Initialbusinessfunds:

Logbook={‘SamKim’:4000,‘MichelSanderson’:4300,\

StarkGarret’:5120,‘AzazelForest’:3230,‘HarrisonSnow’:6300}

Noticethesyntax:

Key:Value

Hereishowthekeysareusedtolookupthecorrespondingvalue,justlikeinadictionary:

>>>print(logbook[“AzazelForest”])

3230

DICTIONARYOPERATIONSYoucanaddnew key:value pairsinthedictionaryaswellasremoveandupdateexistingdictionaryentries.

ADDINGNEWENTRIESTODICTIONARIESToaddnewentriesinyourexistingdictionary,yousimplydefinethemasfollows:

#AddingGabrieltothelogbook:

logbook[‘GabrielSky’]=7300

Theabovestatesthatthekey:value=‘GabrielSky’:7300

DELETINGENTRIESNowwhatifyouwanttodeletesomeentries?Thisisdoneexactlyhowitwasdoneforlists.Nowlet’ssayMichelhasbeenpaidinfull,andhehasresigned.Youwanttodeletehisaccountpermanently.Justlikewiththelists,youuse‘del’:

delphonebook[‘MichelSanderson’]

The‘del’operatorwilldeleteanyvariable,entry,orfunctioninalistoradictionary.Anotherexampleisofasmallinventoryinagrocerystore.Thedictionarycontainsthenamesofvariousfruitsandtheiravailability(numberinstock):

>>>inventory={“apples”:350,“bananas”:230,“Mangos”:100,“Peaches”:250}

>>>print(inventory)

NowwhatifMangosgooutofstock?Wehavetwooptions:ofdeletingthekey:valueorsimplychangethevalueofthekey:

#deletingthevalue

>>>delinventory[“mangos”]

>>>print(inventory)

{“apples”:350,“bananas”:230,“Peaches”:250}

Incasethestoreisreceivingmorestock,theweneedtheoptiontosimplyupdatethevaluewithanewvalue:

>>>inventory[“Mangos”]=0

>>>print(inventory)

{“Mangos”:0,“apples”:350,“bananas”:230,“Peaches”:250}

Let’ssaywehaveanewshipmentforMangowithinthehour,anditwilladd150additionalMangostotheinventory.Thiscanbehandledlikethis:

>>>inventory[“Mangos”]+=150

>>>print(inventory)

{“Mangos”:150,“apples”:350,“bananas”:230,“Peaches”:250}

Tuples,lists,anddictionariesplayanimportantroleinwritingsimplerandmorepowerfulcodesinPython.Theybecomeevenmoreimportantwhenwestartprogrammingusingandinterfacingobjects.

CHAPTER9.OBJECTORIENTEDPROGRAMMING

Historically,acodehasmostlybeenviewedasalogicalprocedurewheredataistakenasinput,processed,andusedtoproduceoutputdata.Consequently,thechallengeofprogrammingwasseenhowtocreatelogicforusingthedataandnotdefiningthedata.

Object-OrientedProgramming(OOP)isaprogramminglanguagemodelthatreliesonbuildingcodeusingobjectsanddataratherthan“actions”and“logic”.Ittakestheviewthatwhatweshouldreallycareabout(andwhichprogrammersalwayshave)areobjectsthatwecanmanipulateinsteadofthesequentiallogicneededtomanipulatethem.

Object-orientedprogramminghasitsrootsinthe1960s,howeveritbecamethedominantparadigmofprogrammingasthecomplexityandsizeofthesoftwarebegantoincreaserapidly,givingwaytomorepowerfulandcomplexsystems.

Examplesrangefromelectronicdevices(whopropertiesandattributescanbenamed),tohumanbeings(describedintermsoftheirattitudesandproperties),allthewaytotheappsweuseonoursmartphones.

GETTINGSTARTEDWITHOOPThefirststepinapplyingOOP(whichyoumustbecausePythonisanobjectorientedprogramminglanguage)istoidentifytheobjectsthatareneededtobuildthecode,andhowtheyrelatetoeachother,andwhichyouwanttomanipulate.

Thoughitiscalleddatamodeling,thinkofitlikebuildingastrategyorablueprintforcreatingsomething.

InPython,onceyouhaveidentifiedandobject,ageneralizedclassofobjectsinitsnameiscreated.Thisclassdefinesthekind/typeofdatathisobjectcontainsandanylogicsequenceswhichitcanmanipulate.

Thelogicsequenceusedforeachclassisknownasitsmethod,whereastheinterfacesthroughwhichtheobjectscommunicatewithoneanotherarecalledmessages.

BENEFITSOFUSINGOOPThisframeworkoffersnewerwaysofprogramminginPython.Importantbenefitsinclude:

Dataclassesallowsaprogrammergreaterflexibilityandcreativityincreatingnewtypesofdataforusewiththeprogram.EvenifcertaindatatypesarenotavailableinPython,youcaneasilycreatethemasaseparateobjectandusethemlikefunctions(crudelyspeaking)insideyourcode.

Thedataclassmakesitpossibletoeasilydefinesubclassesofdataobjectsthatcaneithershareallthepropertiesofthemainclasscharacteristicsorsomeofit.Thispropertyiscalledinheritancewherethesubclassinheritspropertiesandattributes.ThisabilityoftheOOPframeworkallowsmorerobustanalysisofdata,allowsmoreaccuratecoding,andsignificantlyreducesdevelopment.

OOPallowsdatahidingwhichpreventsaccidentalsharingofdataacrossthecode.Sinceeachclasshasapredefinedsetofattributesanddatapropertiesthatitmustbeconcernedwith,anyinstancesofthisobjectwhereusedthroughoutthecodewillonlyuseitsspecifieddata,henceavoidinganyinstancesofdatacorruption.

Classesoncedefinedareeasilyre-useable.Theobjectoncecreatedbecomesglobal,inthesendthatitcanbeusedbyboth,theprogramforwhichitwascreatedandbyotherOOPcodesusingthesamemachine/network.

CHAPTER10.CLASSES,OBJECTS,INHERITANCE

Programmersaresupposedtobelazy.Theyhavetofindthemostefficientwayofdoingthings,savingtimeformorecodingortodowhattheywill.

Thepurposeofprogrammingistosimplyandautomateactionsandhenceavoidrepeatingwritingthesamecodeagain.Recallusingfunctions.Onceyouhavecreatedafunction,youcancallitandre-useitanywhereinthecodeandtheinterpreterwillknowwhatyouareaskingfor.

However,functionshavelimitations.Theyusedatabutcannotstoreandholdinformation.Everytimetheyarecalled,theystartafresh.Nowattimescertainfunctionsandvariablesarerelatedtooneanotherveryclosely,andwheneverthefunctionisrun,thosevaluesneedtobefetchedandcomputedalongsidenewdata.

Butwhatifweneedafunctiontogeneratemultipleoutputsandvaluesinsteadofjustoneoutput?Whatyouneedhereistheabilitytogroupmultiplefunctionsandassociatedvariablesinoneplacesothattheycaneasilyinteractwithoneanother.

Taketheexampleofyourteam.

Allofthemhavejoinedagolfcourseandboughtnewgolfclubs.

Yourprogramwillstoredifferentvariablesregardingtheclubs(theirshaftlength,weight,forgiveness,spin,etc.),andyouwanttokeeptrackoftheimpacteachpropertyexperiencesovertime(weakenedshaft,increasedfrustration,scratches,etc.).Supposeyoumakefunctionsforeachteammember,whatiftheydecidetohavemorethanoneclub?

Willyouwriteawholechunkofcodeforeachdifferentgolfclub?

Giventhatmostoftheclubssharecommonfeatures,theidealthingtodowouldbetocreateabasiccategory,oranidealcategorythatdefinesalltheattributesofthegolfclub.Hence,wheneveryoucreateanewclub,allyouhavetodoisspecifytheneworchangedattributesandanewitemwillbecreatedinthedatabase.

Thisiswhereclassesandobjectscomeintoplay.Theyallowyoutocreatesmallindependent‘communities’wherefunctionsandvariablescaninteracttogether,caneasilybemodifiedasneeded,andremainunchanged(andunaffectedbyothercode).

Westartbuildingsuchobjectsbyfirstcreatingclasses.

CREATINGACLASS

Aclassisablueprint,anideaofsomething.Itdoesnotexistasausablefunction,ratheritdescribeshowtomakesomething.Thisblueprintcanbeusedtocreatealotofobjects.

Youcancreateaclassusingaclassoperator.Thegeneralsyntaxforaclassis:

classname_of_my_class:

[statement1]

[statement2]

[etc]

Here’sanexample

classnew_shape:

def__init__(self,x,y):

self.x=x

self.y=y

shape_details=“Thisisanundescribedshape”

creator=“Noonelaysclaimtocreatingthisshape“

defcreatorName(self,text):

self.creator=text

defdetail(self,text):

self.shape_details=text

defperimeter(self):

return2*self.x+2*self.y

defarea(self):

returnself.x*self.y

defscaleSize(self,scale):

self.x=self.x*scale

self.y=self.y*scale

Theaboveisavaguedescriptionofashape(squareorrectangle).

Thedescriptionisdefinedusingthevariablesyouhaveusedfortheshape,andusingthefunctionsyouhavedefinedtheoperationsthenewclass‘new_shape”canbeusefor.Butyouhavenotcreatedanyactualshape.Itissimplyadescriptionthatneedsvaluestodefinehowitwouldlook(theheight‘x’andwidth‘y’),andwhichwilldefineitsproperties(areaandperimeter).

Wonderingwhat‘self’isallabout?Recallthatyouhavenotcreatedanactualshapeyet.‘self’ishowthingsarereferredtointheclassfromwithinitself.Itisaparameterthatdoesnotpassanyvaluetothefunction.Asaresult,theinterpreterdoesnotrunthecodewhena

classisdefined.Itconsideredasapracticeinmakingnewfunctionsandpassingvariables.

Allthefunctions/variablesthatarecreatedonthefirstindentationlevel(thelineofcodeindentedrightafter)areautomaticallyputintoself.Ifaparameterorafunctioninsidetheclasshastobeusedwithinthatclass,thenthenameofthefunctionmustbeproceededwithaself-dot(self.)e.g.self.xasusedinthepreviouscode.

USINGACLASSWecancreateaclass.So,nowthequestionis:howdoyouusethemagicalblueprinttocreateanactualshape?

Weusethefunction_init_tocreateaninstanceofnew_shape.

Assumingthatthepreviouscodehasbeenrun,letscreateashape:

rectangle=new_shape(80,40)

Thisiswhere__init__functioncomesintoplay.Wehavealreadycreatedaclass(ablueprintnormallycalledaninstancefortheclass).Wedidthisbygivingit:

Aname(new_shape)Valuesinbrackets,whicharepassedpasstothe__init__function.

Usingtheparametersgiventotheinitfunctions,theinitfunctiongeneratesaninstanceofthatclass,assigningitthenamerectangle

Now,thisnewinstanceofournew_shapeclasshasbecomeaself-containedcollectionoffunctionsandvariables(wewilldiscussinheritancelater).Earlierwewereusingself.toaccessthevariablesandfunctionsdefinedinthatclassbecausewewereaccessingitfromwithinitself.Now,wewillusethenamewehaveassignedtoitstangibleform(rectangle).Wewillaccessthevariablesandfunctionsintheclassfromoutside.

Oncetheabovecodehasrun,wecanaccesstheattributesofourclasstocreateashapewiththefollowingcode:

#Calculatingtheperimeteroftherectangle:

printrectangle.perimeter()

#Calculatingtheareaoftherectangle:

printrectangle.area()

#detailsabouttherectangle

rectangle.describe(“Arectanglethatistwiceaslongasitiswide.“)

#Scalingtherectangletohalfitssize,i.e.makingit50%smaller

rectangle.scaleSize(0.5)

Noticehowtheassignednameofthenewobjectisbeingusedwhentheclassisbeingusedoutsideofitself.Whereas,whenitwasbeingusedfromwithinitselfthe self.operatorwasbeingused.

Whenusedfromoutsideofitself,wecaneasilychangethevalueofthevariablesinsidetheclassandaccessitsfunctions.Thinkoftheclasslikeafactorythatassemblesnewproductswhengiventherightinput.Whenusingclasses,wearenotlimitedtoasingleinstance.Wecanhavemultipleofthem.Forinstance,couldcreateanotherobjectnamedthin,long,andsturdyrectangles:

thinrectangle=new_shape(100,5)

longrectangel=new_shape(100,20)

sturdyrectangle=new_shape(100,90)

Evenwhenwehavecreatedthreeinstances,allofwhichreliedonthevariablesandfunctionsfromthesameclass,ALLOFTHEMarecompletelyindependentofoneanotherandcanbeusedcountlesstimesthroughouttheprogram.

APPRECIATINGTHEGEEKTALKTheObject-oriented-programmingisaframeworkwithitsspecificsetofwordsusedtodescribeaprogrammingaction.Youshouldknowthebasiclingotoavoidanyconfusionincompanyofanotherprogrammer.Herearesomebasicwords:

Describingaclassmeansdefiningit(similartofunctions,albeitmoredetailed)EncapsulationisthegroupingofsimilarfunctionsandvariablesunderasingleclassClassitselfcanbeusedintwoinstances,todescribethechunkofcodethatdefinesaclassandtheinstancewheretheclassisusedtocreateanewobject.Aclassisalsoknownasa‘datastructure’.ItcanholddataandhasthemethodstoprocessdataprovidedtoitTheattributeofaclassarethevariablesinsidethemAmethodisthefunctionyouhavedefinedinsidetheclassAclassitselfisanobject,andinthesamecategoryofthingssuchasdictionaries,variables,lists,etc.

INHERITANCEWe’vetalkedaboutinheritanceinfunctionsandearlierinthesamechapter.Whatisitandwhyisitimportant?Let’sfirstrecapwhatwehavedonesofarintermsoffunctions,variables,andcreatingclasses.

Earlieryousawhowwecangroupadiverserangeofvariableandfunctionstogether.Thisallowsthedataandtheprocessingcodetobepresentinthesamespot,makingiteasiertoreadthecodeaswelltoexecuteitacrossthecodefromasinglespot.Now,theattributeswegrantedtotheclass(variables)andthemethodsitcanusetoprocessthedata(thefunctions),allowsustocreateinnumerableinstancesofthatclasswithoutwritingnewcodeforeverynewobjectthatwecreate.

Whatifwewanttocaterananomalyinourdatabase?Imagineifwehaveashapewithadditionalfeatures,onesthatdoessharecommonfeatureswiththeoriginalclassbuthasadditionalfeaturesthattheoriginalclasscannotprocess?

Creatinganewcodetocaterdifferencesisnottherightwaytohandleit.Thisiswherewemakeachildclassthatinheritsallthepropertiesoftheidealclasswhileaddingitsownnewfeaturestoit.

Thisiswhereinheritancecomesintoplay,andwhichPythonmakesexceptionallyeasytoimplement.

Howdoesitwork?

Wedefineanewclass,usingtheexistingclassasits‘parent’class.Consequently,thechildclasstakeseverythingfromtheparentclasswhileallowingustoaddnewfeaturesandattributesandmethodstoit.

Let’sbuildonthenew_shapeclass:

Here’sanexample

classnew_shape:

def__init__(self,x,y):

self.x=x

self.y=y

shape_details=“Thisisanundescribedshape”

creator=“Noonelaysclaimtocreatingthisshape“

defcreatorName(self,text):

self.creator=text

defdetail(self,text):

self.shape_details=text

defperimeter(self):

return2*self.x+2*self.y

defarea(self):

returnself.x*self.y

defscaleSize(self,scale):

self.x=self.x*scale

self.y=self.y*scale

Nowsquareisalsoconsideredaformoftherectangle,howeveritswidthandlengthareequaltooneanother.Nowifwewanttodefineanewclassusingtheexistingnew_shapeclass,thecodewouldlooklikethis:

classsquare(new_shape):

def__init__(self,x):

self.x=x

self.y=x

Thisisquitesimilartohowwedefinedthenew_shapeclass,exceptthatwehaveusedtheparentclassasthesetofparametersthatneedtobeinherited.Noticehoweasyitwastocaterthisnewobjectwithouthavingtoredefineandwriteitscodeseparately.

Wechangedonlywhatneededtobechanged,borrowingtherest.Wehavemerelyredefined__init__functionofnew_shapesothattheheightandwidth(xandy)becomethesame.However,thenewvariablesdefinedinthechildclasswillneveroverwritetheonespresentinnew_shape.

Now,squareitselfhasbecomeanewclassandwecanuseittocreateanotherclassaswell!Youseeapatternhere?Itslikealegopuzzle,youcreateobjectsandyouusethemasbrickstobuildbetterandmorecomplexobjectsandprograms.

Let’screateadoublesquare,sothattwosquaresarecreatedsidebyside:

class2square(Square):

def__init__(self,y):

self.y=y

self.x=2*y

defperimeter(self):

return2*self.x+3*self.y

Noticethatthistimewehaveanadditionalmethod(afunction)inthecodeaswell.Wehaveredefinedtheperimeterfunctionbecausetheonethatsquarehasinheritedformnew-shapecannotcatertotheneedsofthisnewclass.

Ifyoucreateaninstanceof2square,yourdoublesquareswillallhavethesameattributesandpropertiesdefinedbythe2squareclassandnotthesquareornew_shape.

POINTERSANDDICTIONARIESOFCLASSESPreviously,wehadseenhowvariableswappingworks,e.g.var1=var2wouldswapthelefthandsidevariablewiththevaluestoredintherighthandsidevariable.

Thesamedoesnotholdtruewhenitcomestocreatingclassinstances.Whenyouwriteinstance1=instance2,whatisactuallyhappeningisthatthefirstclassispointingtotheclassontheright.“Pointing”meansthatboththenamesofinstancesrefertothesameclassinstance,andthatthesameclassinstancecanbeusedbyeithername.

Thisbringsustodictionariesofclasses.

Buildingonhowpointerswork,Pythonletsuseasilyassigninstanceofclasstoanentryinalistordictionaryaswell.Butwhydoit?What’sthebenefit?

Itallowsustocreatevirtuallyunlimitednumberofclassinstancestorunfromourprogram.Here’sanexampleofusingpointerstocreatedictionaryinstances.Assumingtheoriginaldefinitionofnew_shape,andthatthesquareand2sqaureclasseshavebeenrun:

#Createadictionary:

dictionary={}

#Next,createsomeinstancesofclassesinthedictionary:

dictionary[“2square1”]=2square(5)

dictionary[“longrectangle”]=new_shape(100,30)

Nowyoucanusethemlikenormalclasses!

dictionary[“2square1”].creatorName(“PythonCoder”)

printdictionary[“2square1”].author

printdictionary[“longrectangle”].area()

Now,youhavereplacedthepreviousnamewehadcreatedforourcreationwithanarguablybetternamebycreatinganewdictionaryentry.

CHAPTER11.DEBUGGING

CodesremindusoftheimportanceofpayingattentioninEnglishgrammarlessons,andhowouroverrelianceonauto-correctfeaturesinwordprocessingsoftwarehasmadeussusceptibletooverlookingsmallmistakes—acommahere,acolonthere,andamisspelledvariablethere,amongothers.

Mistakes,weathersmallorlargecanpullthebrakesonaprogram.Asaresult,yourcodewillnotrunatall,displayerrors,orgiveobnoxiousresults.Thisiswhereyouhavetotroubleshoottheprogram,locatetheproblem,andcorrectit.

Inprogramminglingo,that’scalleddebuggingyourprogram.

Smallmistakessuchaswrongsyntaxordeclaringnon-existingvariables,ormorefundamentalmistakessuchasinsufficientunderstandingoftheproblem(andhencetheobjectsthatneedtobecreatedandtheirinteraction),andincorrectflowofdatacanmakethecodedysfunctional.

Giventhatonlyyoucanbestunderstandyourcode,youwilloftenfindyourselfinapositionwhereyoualonearerightpersontosaveyourcode.However,decadesoftestinghavegivenusafewtipsandtricksfordebuggingyourcode.

However,beforewemoveintothetips,itisimportantthatyoudownloadyourfirstdebugger.

DOWNLOADADEBUGGER

Why?

Pythonalreadyshipsinwithitsbuilt-indebugger.

Yes,Pythoncomesequippedwithadebugger,sportingabasiccommandlineinterfaceandwithvariousfeaturesandoptions.However,itlackscertainfeaturesthatwillsimplifydebuggingforbeginners,includingstacktracesanddifferentiatingcoloringfordifferenttypesofcode.

So,here’sabetteroptionforadebuggingtool.

DownloadPudb2015.3,afullscreenconsolebasedprogramdebugger.IthasamodernGUI-basedenvironment,andallowsyoutodebugyourcoderightwhereyouwriteit:ontheterminal.

CHAPTER12.NEXTUP

ThiseBookismeanttointroduceyoutothebasicsofPythonlanguage:itsfundamentalbuildingblocks,theirsyntax,theirbasicuses,andhowtheyarerelatedtooneanotherincreatinglargerprograms.However,likeanyotherlanguage,theonlywaytoimproveandexcelatitistoconsciouslytrytouseittosolveproblems.

Havingintroducedthebasicbuildingblocksofthelanguage,it’snowlikechess:youknowthecomponents,youknowthebasicrules,andyouknowthemoves(bothlegalandillegal).Readingmoreaboutitwillnothelpyouontheboard.Onlypracticewill.

Sowhatshouldyoudonext?

Pythonisalanguageforcommunicatingwithcomputingdevices,andmostofwhatyouwillbewritingwillneverbevisibleonthefrontend.Imean,howmanyappshaveyouused,orgameshaveyouplayedwhereyouknowthecodelineyou’reonrightnow?

Understandthatyouhaveonlyscratchedthesurface.Asyoustartbuildingcodewiththebasics,youwillcomeacrossadvancedcodesthatyoucanbuildon.ContinuepracticingandsharingyourquestionswithablossomingonlinecommunityofPythoncodesandfans.

PythonisoneofthemostadvancedandoneofthesimplestOOPlanguagesontheplanet.Bepatient,andmasterthebasicsbeforemovingtowardsthemoreadvancedfeaturesofthelanguage.

ABOUTTHEAUTHOR

Inspiredbylegendaryfemalecoder,AugustaAda,VivianhasbeeninthesoftwareengineeringsinceshewasincollegeattheUniversityofSydney,Australia.WhilestudyingatUofS,Viviantookthepathmostfemaleswouldnotstudy.SheenrolledintendingtomajorinArchitecture,butafter2semestersshebegantodesignwebsitesforlocalcharities.HerloveofthewebtookoffandswitchedmajortoComputerScienceandInformation.

Sincegraduatingin2012,Vivianashasgoneontodoawidevarietyoffreelanceprojectsandsub-contractworkinmobileandwebdevelopment.Sheoftenvolunteersinworkshopsandtrainingprogramstohelpthoseinterestedinlearningallaboutsoftwaredevelopment.

Viviantravelstheworldandworksfromherlaptopmostofthetime.Sheisinterestedinhelpingotherslearnhowtoprogramandstartnewcareersinthewebindustry.

ONELASTTHING…IfyouenjoyedthisbookorfounditusefulI’dbeverygratefulifyou’dpostashortreviewonAmazon.YoursupportreallydoesmakeadifferenceandIreadallthereviewspersonallysoIcangetyourfeedbackandmakethisbookevenbetter.

Thanksagainforyoursupport!