python中文汇总-英文introduction-to programming with for beginners

IntroductiontoProgrammingwithVivianCopyright©2015bySoftwareDevelopment欢迎加Python欢迎加Python编程学习交，群里免费提供500+本Python书籍 .ThisbookcontainsmaterialprotectedunderInternationalandFederalCopyrightLawsandTreaties.Anyunauthorizedreprintoruseofthismaterialisprohibited.Nopartofthisbookmaybereproducedortransmittedinanyformorbyanymeans,electronicormechanical,includingphotocopying,recording,orbyanyinformationstorageandretrievalsystemwithoutexpresswrittenpermissionfromtheauthor/Anyunauthorizedbroadcasting;publicperformance,copyingorre-recordingwillconstituteaninfringementofcopyright.Permissiongrantedtoreproducefor alandeducationaluseonly.Commercialcopying,hiring,lendingisprohibited.Maybeusedfreeofcharge.Sellingwithoutpriorwrittenconsentprohibited.Obtainpermissionbeforeredistributing.InallcasesthisnoticemustremainFurtherLimitOfLiability/Di erOfWarranty:ThePublisherAndTheAuthorMakeNoRepresentationsOrWarrantiesWithRespectToTheAccuracyOrCompletenessOfTheContentsOfThisWorkAndSpecificallyDi AllWarranties,IncludingWithoutLimitationWarrantiesOfFitnessForAParticularPurpose.NoWarrantyMayBeCreatedOrExtendedBySalesOrPromotionalMaterials.TheAdviceAndStrategiesContainedHereinMayNotBeSuitableForEverySituation.ThisWorkIsSoldWithTheUnderstandingThatThePublisherIsNotEngagedInRenderingLegal,Accounting,OrOtherProfessionalServices.IfProfessionalAssistanceIsRequired,TheServicesOfACompetentProfessional ShouldBeSought.NeitherThePublisherNorTheAuthorShallBeLiableForDamagesArisingHerefrom.TheFactThatAnOrganizationOrWebsiteIsReferredToInThisWorkAsACitationAnd/OrAPotentialSourceOfFurtherInformationDoesNotMeanThatTheAuthorOrThePublisherEndorsesTheInformationTheOrganizationOrWebsiteMayPror mendationsItMayMake.Further,ReadersShouldBeAwareThatInternetWebsitesListedInThisWorkMayHaveChangedOrDisappearedBetweenWhenThisWorkWasWrittenAndWhenItIsRead.Everyefforthasbeenmadeinthepreparationofthisbooktoensuretheaccuracyoftheinformationpresented.However,theinformationcontainedinthisbookissoldwithoutwarranty,eitherexpressorimplied.Neithertheauthor,norLearntoCodeProductions,anditsdealersanddistributorswillbeheldliableforanydamagescausedorallegedtobecauseddirectlyorindirectlybythisbook.TableofTableofChapter1.WhyYouShouldLearnProgrammingChapter2.WhyPythonisthePerfectLanguageChapter3.GettingStarted:Pre-reqsChapter4.Variables,Expressions,Statement,StringsChapter5.FunctionsChapter6.Conditionals,FlowControl,DecisionsChapter7.IterationsChapter8.Lists,Dictionaries,TuplesChapter9.ObjectOrientedProgrammingChapter10.Classes,Objects,InheritanceChapter11.DebuggingChapter12.NextWhyThisTheadage“penismightierthansword”isbestservedbyprogramminglanguages.Youliterallytypeandcommunicatesolutionstoproblemsonacomputer,anditcomestoThisbookintroducesPython,thesimplestandcurrentlyoneofthemostpowerfulObjectOrientedProgramminglanguagesontheplanet.ThebookshowshowitissimilartolearninganewdialectofEnglish,onemeantforthecomputingdevicesyouholdinyourItwillintroduceyoutothebasicsofPythonlanguage:itsfundamentalbuildingblocks,theirsyntax,theirbasicuses,andhowtheyarerelatedtooneanotherincreatinglargerThisbookismeantfornovicesandbeginners.Hence,itusessimplereallifeexamples,offersshortcodeswithexplanations,andcontinuouslylinksbacktoearlierchaptersandbuildsonthem.Chapter1.WhyYouShouldLearnTheriseofsmartdevices,wirelessconnectivity,andincreasedusermobilityinofficesmadecomputersanintegralpartofourlifestyles.Asourrelianceonsmartdevicesandvariousappstocompleteadiverserangeofactivitiesincreases,learningtocodeisingakintolearningasecondNormally,welearnsecondlanguagestoincreaseourreach, egeographicandculturalbarriers,andtobeabletocommunicatewithpeoplefromdiversecultures.Smartdeviceshavebroughtdownbarriersacrossdifferentcultures,andhave eoneofourmosttrustedcompanions.However,wearenotabletoeffectivelycommunicateandinstructoursmartcompanionstoperformtheactionsthatwedesire.Learningtoeffectivelycommunicatewithcomputersandsmartdevices,andbeingabletoinstructthemtoperformdifferenttasksisfast ingsomethingmorethananaddedskill—itis ingpartofwhatitmeanstobehumaninofDigitalNatives.7ReasonsforLearningtoLearntoprogramandyouwillbeabletoexperiencethefollowingseven,awe-inspiringrealitiesofbeingaDigitalNative.It’stheonlytimewhenwritingcanliterallysolveTheadage“penismightierthansword”isbestservedbyprogramminglanguages.Youliterallytypeandcommunicatesolutionstoaproblemonacomputer,anditcomestoIt’samazingtorealizehowpowerfulthisformofcommunicationis.MostofsmartphoneusershavevisitedAppStoresandseenarangeofapps,eachsolvingauniqueproblemforus.Knowingaprogramminglanguagemeansthatyoucanbreakaproblemintosmallerproblemsandcreateprogramsforyourselfandothers.Somanyproblems,nomatterhowtrivialcannowberesolvedsimplybywritingthemoutinaprogramminglanguage.ProgrammingtransformsyourcomputerandsmartphoneintoaHumanslandedonthemoonrelyingoncomputingpoweratleasta1000timeslesspowerfulthanthecomputingpowerofoursmartphones.By2016,over2billionpeoplewillbeusingsmartphonesacrosstheglobe.Justimaginewhatthisprocessingpowercanbeputtousefor.ImaginewhatyoucancreateanddeveloponyourPCforusewithyoursmartphones: alizedapps,games,tools,andmore.ThepossibilitiesareProgrammingsimplifiestasksbyautomatingWeliveinaworldwhereefficiencyisthehallmarkofeverything.Nobodywantstoperformtediousandrepetitivetasksifyoucanpayforasolutionthatcanautomateit.Thisrangesfromofficetasksto alones.Bylearningtocode,youcancreatesimplescriptsthatsimplifytasks.Thinkofgeneratingmacrosin Office(ExcelandWord)orscriptsthatsimplifytasksyouhavetoperformregularlyatworke.g.creatingfoldersforprojects,completingforms,creatingshortcuts,addingmorefeaturestoexistingsoftware,etc.Itdevelopsyourability anddisciplinedInstructingcomputersrequiresthatgivethemstep-by-stepinstructionsthatlinkpre-determinedinputstoexpected es.Tocommunicatetothecomputer,youhavetowriteinanexplicitlanguage,fromproblemtosolution.Thisrequiresbreakingdownproblemsintosimplerones,andthenorganizingthemintoinputsandProgrammingteachesyoutoorganizethoughtsandbreakdownaproblemintoconstituents,identifyingexternalfactorsandtriggers,osimplerchunksofprogrammablecode.Thistrainsyourmindtothinkclearlyandsystematically,filteringoutinformationthathasnobearingsonthesolution,andfindingthesimplestsolutiontotheproblem.FuturejobswillrequiresoftwareCurrently,programmingmaybeaskilltoboastyourchancesofentryintothemarket,howeverasorganizationsfocusonincreasinginterdepartmentalcollaboration,theybegintopreferpeoplewithinter-disciplinaryskillsets.Inthelongrun,beingabletoprogram easkillneededtosurviveinthetechnologymarket.Becauseit’snothardtoIfyoucancomprehendEnglishlanguage,learningtoprogramissimplyamatteroflearningthelogicbehindprogrammingwords.Overtheyears,programminglanguages emoreintuitive,utilizingcommandsthatclearlystatetheirpurposeandhenceallowyoutonearlyconstruc tences“If-Then”,“Else”,“Print”,“Switch”,arejustthemostcommonlyusedcommandsinprogramminglanguage.Allyouhavetoslearnthegrammar,andwithpracticeyouwillbeabletowritethoseshortessaysthatidentifytheproblem,itscomponentsandinputs,andtheoutputsforeachprogramminghasgreatEarningAsyougetbetteratprogramming,youcaneasilyleverageyourproblemsolvingskillstodevelopsoftwareforsale.Thisincludesworkingasafreelancer—buildingapps,develocustomsoftware,creatinganddesigningwebsites,orhelclientscompletetasksusingexistingsoftwareandplatforms ExcelandWord,Flash,Java,InConclusion—PreparetoProgrammingisanadd-ontoyourcurrentunderstandingoftheEnglishlanguage.Thinkofitasanewdialect,onethatyourcomputerandsmartdeviceunderstands,onethathasalotofbenefitsinthemodernworld,iseasytolearnandonethatwillsoon eamusthavefordigitalnatives.Chapter2.WhyPythonisthePerfectInanagewheremachinesare inghighlyin ligentandarecontinuouslysimplifyinghuman-machineinteractions,itonlymakessensetouseanin programminglanguage.ExistingstaticallytypedlanguagessuchasPascal,C,orothersubsetsofC++andJavaintroduceverbosesyntaxthatcloudtheactualprocessofproblem positionanddesignofdatatypesthathavetobeprogrammed.Hence,forsomeonewhodoesnotknowhowtocode,theselanguagesseemunnatural.Furthermore,theadditionalcomplexityofthesyntaxonlyslowsdownthepaceofingrainingthemethodologyofprogramming.ThisiswherePythonbringsinthepowerofsimpleandconsistentsyntax,backedbyalargestandardlibrarywithrealproblems.NotwithstandingtheriseinitspopularityinAmericancollegesasreportedbytheAssociationforComputingMachinery,PythonhaseffectivelyreplacedJavaasthefirstlanguageofchoiceforbuddingprogrammers.SowhatismakingPythontheperfectlanguageaftertwodecadesofbeinginthe#1—MinimalInstallingandrunningPythonisextremelysimple.Allyouhaveto sdownloadthefileandeitherrunitthroughtheTerminalprogram(forMac),orthePowerSprogram(Windows),andLoandbehold!You’rerunningPython.#2—WritingaprogramisakintowritinginPythonisauniversallanguage.Thismeansthatitssyntaxandcodinglingoisexceptionallysimplifiedandeasy.PythonistheclosestthingtowritingalogicalargumentinEnglish.Thecommandsaresimpleandtheadditionalbaggageofgrammar(programmingsyntaxsuchasbrackets,colons,quotes,etc)isminimal.Yougrasphowtosystematicallybreakdownaproblemintosimplersteps,andyoucaneasilycodeitinPython.Inaphrase:agreatfirstexperienceforanyThestandardfirsthands-onprogrammingexperiencethatallbeginnersgothroughistoprintsomethingonthescreenusingcoding.Thisisnormallythewords“oWorld”,amongothers.Pythonmakesitliterallyamatterofwritingao Comparethistothefollowing publicstaticvoidmain(String[]args) o, Furthermore,whenyoumoveaheadintothecourse,otherexamplesofsimplifiedprogrammingwillleapout,includingsimplereading/writingofinformation,stringprocessing,GUI’s,websitecode,Databases,websites,etc.Itssimplicityandeaseofprogrammingisthereasonwhyithasbeenadoptedbysomanypeopleandforsuchawiderangeoftasks.Thisisfurthermadeenjoyablebythefactthataverylargecommunityofenthusiasticdevelopersisalwaysabuzztoaidnewcomerseinitiatedintothe#3—PythoniseasytoPythonisdesignedtobeaneasy“Readability”ofacodemayandseemunimportantrightnow,butit esthedefiningfactorwhenthecode eslargerandmorecomplex.Readabilityisveryimportant,becauseunlikeacoursebook,thechapters(orchunksofcode)arenotalwaysarrangedtoworkinastep-by-steporlinearorder.Attimescodingblocksinthefarrecessesofthecodeneedtobecalledearlier,orlater,multipletimesthroughoutthecode,andsoon.Easeofreadabilityisimportantforsharingacodebetweenateam,fortroubleshootingaprogram,andformakingchangestoit.Intraditionallanguages,reading increasinglydifficultasbecauseofallthenon-Englishgrammaticalsyntax.Pythonusesindentationtogivestructuretothecode,andthoughprogrammerswhoaremigratingfromadifferentlanguagetoPythonmaybeheardcomplainingaboutthelack(andnearabsence)ofbraces,itisoneofthekeybenefitsofPython:itsimplyde-clutterstheworkenvironment!Thinkofindentationsliketheheadingsinyourwordprocessingsoftware(H1,H2,H3,H4,H5,andsoon).Incodingtheheadingsarenormallycurlybrackets(“{}”)thathavetobeaddedatthestartandendoftheparagraph.Asaresult,twotypesofcommunicationarehappeningsimultaneously:bracestolthemachineabouttheprogram,andtheindentationstolthereader(anotherprogrammer)whattheprogramisabout.NowimagineNOThavingtoaddbracketsandindentationandfollowalegendyouhavecreatedearliertokeepyourprogramreadable.Pythondoesthisbyofferingasinglestructuretodenoteaprogram:makingiteasierforhumansandcomputersaliketoreaditwithease.#4—YoudonothavetocompiletheprogramtorunWhenyou’relearningsomethingnew,mistakesareboundtohappen.Howthosemistakesareshowntoyouoftenplaysacrucialroleinhowmotivatedyouaretotryagain,orhowaffectedyouarebythemistakethatyouhavemade.WithPython,allerrorsareidentifiedatruntimeinsteadofshowingafailuretocompileerror.Thismakesiteasiertoidentifyandfixmistakesimmedia Thisisincrediblyusefulwhenyouwillbedesigningacomplexalgorithmwherechangesaremadecontinuously.Whereotherprogramminglanguageswillwastetimetakingyouthroughthecompile-run-debugcycle,Pythonsimplyshowstheresult(ortheproblem)inthesameinterpreter.Hence,youcanmakeinnumerablechangestoapieceofcodeandexecuteitinreal-timeintheinterpreter.Thisbooststhelearningprocessasyoucanconsciouslymakeerrors,seeitsimpact,andtroubleshoottheprogram.Thisdramaticallyreducesthedevelopmentcycle, esespeciallyusefulforrapidprototyofyourcode.#5—PythonisPythonisanopenontwoOpensourceasprogrammingBuiltusingOpenAsanopensourceplatform,itsliberaldistributionlicenseallowsthelanguagetobeusedforcodingprograms/appsthatcanseamlesslybeintegratedasanextensionofotherproprietylanguages.Intermsofcodingarchitecture,Pythonisgreatatintrospectionbecausethecodeisbasedondiscretechunksofprograms(knownasobjects).Wewillgettechnicallater,butforthemoment“beingopen”meansthatitwillbereallyhardforyoutowritedirtycodeorsidesteppropercodingmethodstosolveproblems.Hence,Pythonforcesyoutowritebettercodefromthebeginning,andthisprovesveryhelpfulduringdebugging.欢迎加Python编程欢迎加Python编程学习交，群里免费提供500+本Python书籍Chapter3.GettingStarted:Pre-ThereareonlytwoprerequisitesforgettingstartedwithinstallingandusingPython:Reasonableknowledgeofusingacomputerandinternet.Acompellingdesireforlearninganewlanguageforcommunicatingwith欢迎加Python欢迎加Python编程学习交，群里免费提供500+本Python书籍InstallingPythononDownloadthelatestversionofPythonfromtheofficialWebsite.NOTE:NOTE:Twoversionsofthelanguageareavailable,Python2.xandPython3.xThedifference,inallitssimplicityisthatPython2.xislegacyi.e.itistheonethathasbeeninstalledonmostdevicesandhenceisthecurrentnormforPython,whereas,Python3.xisthepresentandfutureofthelanguage.TheWindowsversionisdownloadedasanMkage,andcanbeinstalledwithadouble-clickontheopensfile.AllowthewizardtoinstallPythontothedefauForPython3.xitwillbeC:\Python3x\—(xbeingreplacedbytheversionyou’vedownloaded,thelatestbeing2.7)NOTENOTE:ThedifferentfoldersmeanthatyoucaninstallmultipleversionsofPythononthesamesystemwithoutcausingany However,asingleinterpreteractsasthedefaultapplicationforPythonfiletypes. That’sit.YoucanusePython;however,itis mendedthatyouinstallthelibrariesandtoolsdescribednextbeforeworkingonwritingyourcode.Inparticular,Setuptoolsisamustinstallasitallowsyoutoeasilyuseotherthird-partyPythonlibraries.Setuptools+FromalltheSetuptools,thisisthemostcrucialthird-partyPythonsoftwarebecauseitextendsthecapabilitiesofthepackagingandinstallationfacilities(offeredinthedistutilspresentinthestandardlibrary).OncetheSetuptoolsisaddedtoyourPythonsystemanddirectory,allPythoncompliantthird-partysoftwarecanbeaddedusingasinglecommand.Furthermore,withtheSetuptoolsinstalled,youcanaddanetworkinstallationcapabilitytothesoftwarethatyouPython3,generally,comesequippedwithPIP.YoucandownloadthelatestversionoftheSetuptoolsforWindowsHERE.NowinstallPIP,areplacementforthePythoncommandeasy_installandwhichintroducesun-installationofdifferentpackages.VirtualNext,youhavetoinstallaVirtualEnvironment,virtualenv,atooltokeepeach欢迎加入非Python编程学习交 ，群里免费提供500+本Python书籍self-containedandseparatefromoneanother.Thinkofitthisway:whenyouwriteacode,itleveragesthePythonworkenvironmenttoreduceitssize(e.g.usingsomepre-madefunctionsfromthePythonlibrary).Hence,whenitissaved,onlytheessentialinformationneededforthesavedfiletobereopenedandruninthePythonworkenvironment.NowyoucreateanothercodeandsaveNowthenewprojectmayusedifferentlibraryobjectsfromPython,however,unlessamechanismexiststokeeptheirrelianceseparatefromoneanother,oneprogramcaneasilywiththeAvirtualenvironmentseparatesalldependenciesrequiredbydifferentprojectsinseparateplaces.Hence,eachprogramcansafelyruninitsownsafehaven.DownloaditfromThesecondAstrongdesiretolearnhowtowritecomputerIfyoudon’tknowhowtoprogramandarenewofPython,thenunderstandthataswithanynewlanguage,ittakestime,practice,andperseveranceinfaceofmistakesandsmallfailures.Hence,youmusthaveastrongdesiretolearnthelanguagetosucceed.StrongdesiretoPythonrequiresfocusedeffortinlearningthebasics,learninganewmethodforlogicallybreakingdownaproblemintoconstituentparts,learninganewprogrammingmethodology(Pythonisanobjectorientedprogramminglanguage),andpracticingcodingbehaviorinanewcodingenvironment.Don’texpectamiracletoYouwon’tlearnitbysimply ofthisAswithanylanguage(spokenorcoded),practiceandexperiencematteralot.Simplyreadingandmemorizingsyntaxwillnotbringamiraculoustransformationandmakeyouanaptprogrammerinthefield.Unlessyouarewilledbyatruedesiretolearnthenewlanguage,learningtoprogramcaneboring,mistakeswillcompoundasade-motivatingfactor,andyouwillnotingraina yticprocessofbreakingdownproblemsandwritingPractice,morepractice,andevenmoreAlllanguagesarelearnedbyrepetitionandYouhavetolearnhowtoputtogetherphrasesandcreatemeaningfulsentencesoutofthem.WithPython,itisaboutusingthesyntaxandcommandstocreatechunksofcodethatcanperformanaction(takeinput,compute,displayanoutput,etc.),anddosoThisbookwillofferyouthebasicsofthelanguage,butyoumustwillyourselftoputyourbraininhighgearandwriteALOTofcodefordifferentproblems.Onlythenwilltheinformationthatissharedinthisbookwillstickwithyou.Thinkofthethingsyouhave egoodatovertheyears:talking,surfing,gaming,playingmusic,generalknowledgeaboutfashion,writinggoodessays,humor,andmore.Allofthemneededtobepracticedagainandagaintogainsufficientcommandandconfidenceinyouabilities.ProgrammingwithPythonisquitesimilartothatChapter4.Variables,Expressions,Statement,RememberthoseEnglishgrammarlessons?How“eachsentence”ismadeofasubjectandanobject,hasnouns,pronouns,auxiliaryverbs,andadjectives,andthelike?Justrememberhowwordsandauxiliaryverbswereusedtocreatesentences,andhowthesesentencesareusedtocommunicatemorecomplexthoughts.ThisiswhatwearegoingtodoPython(andmostotherprogramminglanguages)aremadeofsomeuniversalbasiccomponents.Theseinclude(inorderofincreasingcomplexity)variables,expressions,statements,andstrings.Thenamesareself-explanatory.Let’sseetheminAvariableisthe“x”youtriedtofindinmostofyourmathclasses.InprogrammingitisdatatypecapableofcontainingchangeableTheabilitytomanipulatevariableinaprogramminglanguageisoneofthemostpowerfulfeaturesinthecodingworld.Hence,wemustbeginbyunderstanding“values”inValuesanddataValuesarecategorizedaccordingtothetypeofdatatheycanhandle.Forexample,“o,Programming!”,“2”,and“2.3”areallconsideredvaluesinPython,excepteachbelongstoadifferentcategoryordifferentdatatype.NOTE:NOTE:Datatypedonatesthedifferenttypesofdatathatcanbeusede.g.characters,numbers,floatpoint(decimalnumbers),etc.Thenumeric2isanintegerbecauseitcontainsawholenumber,whereasthe“ Programming!”isastringbecauseitcontainsastringofletters,and“2.3”isafloatbecauseithasdecimalnumber.YourPythoninterpreterisabletoidentifyandusestringsasasinglevalueenclosedwithinthequotationmarks.Ifinconfusionaboutthetype,let lyouthedatatypeofyourvaluewiththe()>>>>>>type o, <type >>>type <type Notethatthestringsarealwayscontainedwithinquotes“”.Hence,ifyouweretoputnumericvalueswithinthesequotes,theyautomatically estrings.>>>type <type Furthermore,whenwritingstrings,avoidusingcommastoseparatetens,hundreds,andthousands.Forexample,ifyouwanttowritetwohundredthousandas2,00,000,Pythonwouldreafollows:>>>print(2,000,000) 20 UnexpectedThat’sbecausecommasareinterpretedbyPythonasseparators.Hence,youseethreevalues:2,0,and0.NOTE:NOTE:Thesyntaxforprintisprint(x)with‘x’beingreplacedbystrings(“string”)ornormalnumericvalue(2)ThisThisisdifferentfromPython2,wherethesyntaxissimply:printx,print2,orprintOthertypesincludefloat(fordecimal>>>type<type>>>type<typeNOTE:NOTE:Youcanuseboth,single(‘’)anddouble(“”)quotesforwritingstringsinPython.AND,youcanusedoublequoteswithinsinglequotes.Forexample:(‘Hesaid,“Loandbehold!”‘)Let’sstartwithRememberhowbasicequationswerecreatedinQuestion:IfSamboughttwoeBooksfor$3,howmuchwillitcosttopurchase5eBooks?Wenormallybeganwithsupposing“x”asthecostof5eBooks.Oncesupposed,“x”canbeusedanywhereinthesolutionandanyonecaneasilyfigure(interpret)that“x”isreferringtothe“Costof5eBooks”definedinthebeginning.Inprogramming,avariableisthenamethatreferstoachangeablevalue—onethatcanbechangedandautomaticallyupdatedatwill.Likemath,variableshavetobedeclared/created(supposed)andthenassignedavalue.Inpython,thevalueofavariableisassignedusingtheassignmentstatement:>>>message>>>message=“I’mprogrammingwith>>>x=>>>yr=Noticehoweachtypeofdataisassignedinasimilarmanner,startingwithastring,aninteger,andafloatingpointnumber.Themostimportantthingistheequalsign“=”thatseparatesthenameofthevariable(lefthandside)fromthevalueofthevariable(righthandside).Theequalsign“=”isknownastheassignmentoperator.Theleft-hand,right-handdivideisarule.Deviationisnotpermitted.Ifyoureversetheorder,it esmeaninglessfortheinterpreter.Hence,thefollowingmakesno>>>“I’m>>>“I’mprogrammingwithPython!”=>>>2015=>>>365.25=TypesofVariablesalsohavetypes.Intheexampleabove,themessageisastring,‘x’isaninteger,and‘yr’isafloat.Youcanverifythetypeofthevariableusing>>><type>>>>>><type>>><type>>><typeNotehowthetypeofthevariablecorrespondstothetypeofthevalueitNamingYourVariables,TheCertainnamingconventionsareusedwhennamingvariables.Thesearesimplystandardsthatareusedtostandardizehowcodeiswrittenandtokeepitclean.Thisgainsimportanceasyourcodegetslongerandyourvariables emoredescriptive.Additionally,certainpythonruleslimithowyourvariablecanbeassigned.YourvariableAlwaysbegin Neveruseillegalcharacters($,&,*,NeveruseaPythonTherefore,thefollowingwillresultinsyntax>>>14numbers=“What>>>14numbers=“WhatarethosefourteenSyntaxError:invalid>>>Increase$=SyntaxError:invalid>>>class=“PythonBasicsSyntaxError:invalidNow“class”isaPythonkeyword,whi eansitispartofitsrulesandstructure.Pythonhasthirty-onesuch Keepthistablehandy,andiftheinterpretercomplainsaboutsyntaxerror,checkyourvariablenaming!Likenormallanguage,astatementisaninstruction.InPython,youcanexecuteprimarilytwokindsofstatements:printandassignment.Theformerproducesavaluewhilethelaterdoesnothing.Whenyouwriteastatement,theinterpreterexecutesitandtriestodisplayprint(3) t= print Theabovecodewillproducethe TheassignmentstatementusedforcreatingavariableproducesnoAsinlanguage,anexpressionisacompletethought,withapremiseandaconclusion.Inpython,anexpressionhasinputs,adefined/expecteduseofthoseinputs,andanexpectedwayofeitherdirectlydisplayinganoutputorcomputingittodisplayanoutput.Generally,meaningfulexpressionsareacombinationofvariables,values,statements,andoperatorsthatforcestheinterpretertoevaluateitanddisplayresults:>>>>>>1+2Avalueandavariableitselfaresimpleexpressionsin>>>>>>>>>However,theseexpressionssimplyprint/displaytheexpression.Evaluatinganexpressionisnotsimilartosimplyprintingavalue.Takethe>>>message>>>message=“Writing>>>“WritingNoticehowthequotationmarksaredisplayedintheoutput.However,whenusingprint(),onlythecontentsofthestringaredisplayed:>>>>>>printWritingThisisbecausetheprint()statementfetchesthevalueofthevariable(theNow,anexpressionallbyitselfisalegalstatement.Youcanwriteasmanyasyouwant,butunlessyouusecertainoperatorsandcommandstocommunicatethepurposeoftheexpression,NOOUTPUTwillbedisplayed.Forinstance:“Python,“Python,13+NooutputwillbeThisiswhereoperatorsandoperandscomeintoOperatorsandAcodeissupposedtoperformcertaincomputationsontheexpressionstogeneratepredictableoutputs.Computationsareperformedusingoperators—specialsymbolswhichyoumaythinkofasshortformsfordifferentThevaluethattheoperatorusesiscalledanoperand.Herearesomet-t-(1+2+3)*(6-Howthesymbolshavebeenused+,-,/,*(formultiplication)arethesamewaytheyareusedinmathematics.Now,whenavariableisusedwithoperator(s)tocreateanexpression,theinterpreterfetchesandcomputesthevalueassignedtothatvariable.However,thereisacaveat.Thoughaddition,multiplication,subtraction,andexponentiation(representedbythedoubleasteriskoperator**)haveasingleuseandgenerateanexpectedresult,divisiondoesnot.Let’ssaythefollowingexpressionis>>>t>>>t=>>>Butwhatifwantedtoperformanintegerdivisionwheretheanswerisalwaysroundedofftotheclosestintegervalue?Let’s>>>>>>Thisiswhere“//”isusedtoindicateour>>>>>>2Anotherwayof ingistoassigndatatypestotheanswer(afloat),butwewillcometothatlater.OrderOfYoucanusemultipleoperatorsinasingleexpression;howevertheirevaluationisdependedontherulesofprecedence.Pythonfollowsthesameruleasisappliedformathematicaloperators.RememberPEMDAStomemorizetheorder:Parentheses—Expressionsintheparenthesisarealwaysevaluatedfirst.Hence,3*(4-1)is9.Parenthesisarealsoagreatwayformakingiteasiertoreadtheexpressionsuchas(t*100)/60Exponentiation—(**)hasthenexthighestprecedence.Hence,3**1+1is4andnot9,whereas4*1**3is4andnot64.MultiplicationandDivision—Bothhavethesameprecedence,albeithigherthanadditionandsubtractionAdditionandSubtraction—Alsohavethesameprecedence,albeitlowerthanmultiplicationanddivision.Whatifmultiplicationanddivisioncomeinthesameexpression?Forexample:t*100/60Operatorsthathavethesameprecedenceareevaluatedfromtheirappearancefromlefttoright.Hence,intheexpressiont*100/60,multiplicationhappensfirst,followedbyOperationsandGenerally,youcannotperformanymathematicaloperationsonstrings.Thisincludesinstanceswherethestringslooklikenumbers,oronlyhavenumbersinthem.Thefollowingexampleshowsanillegalmathematicaloperationonasetofstrings:mess