__init__ in Python: An Overview | Udacity

The __init__ method is the Python equivalent of the C++ constructor in an object-oriented approach. The __init__ function is called every time ... 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Inthisarticle,we’llreviewtheparadigmofobject-orientedprogrammingbeforeexplainingwhyandhowtousethe__init__method.  WhatIsObject-OrientedProgramming? Object-orientedprogramming(OOP)isaprogrammingpatternthatconsistsindefiningobjectsandinteractingwiththem.Anobjectisacollectionofcomplexvariablesandfunctionsandcanbeusedtorepresentrealentitieslikeabutton,anairplane,oraperson. Todeclare,initialize,andmanipulateobjectsinPython,weuseclasses.Theyserveastemplates fromwhichobjectsarecreated.Thefollowingdiagramillustratesthisidea: Wecanseeintheabovediagramthatthedogclasscontainsspecificdogcharacteristics,suchasbreedandeyecolor,aswellastheabilitiestorunandwalk.Let’sstartbydefiningaclassinPython. WhatIsaClass? Aclassdefinesandstructuresalloftheobjectsthatarecreatedfromit.Youcanviewtheclassasanobjectfactory.Let’staketheexampleofafoxterrier—abreedofdog.FromanOOPstandpoint,youcanthinkofdogasaclassthatincludesadog’scharacteristicssuchasitsbreed,oreyecolor.SinceaFoxTerrierisadog,wecancreateadogobjectthatwillinheritthecharacteristicsofitsclass.Classesusemethodsandconstructorstocreateanddefineobjects. User-DefinedAndSpecialMethods Methodsarefunctionswithinaclassthataredesignedtoperformaspecifictask.Pythondifferentiatesbetweenuser-definedmethods,writtenbytheprogrammer,andspecialmethodsthatarebuiltintothelanguage.Auser-definedmethodisafunctioncreatedbytheprogrammertoserveaspecificpurpose.Forinstance,adogclasscouldhaveawalk()methodthatthedogobjectcanuse.Theprogrammercreatesthismethodandhasitperformspecificactions. Specialmethodsareidentifiedbyadoubleunderscoreateithersideoftheirname,suchas__init__.Pythonusesspecialmethodstoenhancethefunctionalityofclasses.Mostofthemworkinthebackgroundandarecalledautomaticallywhenneededbytheprogram.Youcannotcallthemexplicitly.Forinstance,whenyoucreateanewobject,Pythonautomaticallycallsthe__new__method,whichinturncallsthe__init__method.The__str__methodiscalledwhenyouprint()anobject.Ontheotherhand,user-definedmethods,likestefi.run(),arecalledexplicitly. TheConstructor Aconstructorisaspecialmethodthattheprogramcallsuponanobject’screation.Theconstructorisusedintheclasstoinitializedatamemberstotheobject.Withourdogclassexample,youcanuseaconstructortoassigndogcharacteristicstoeachFoxTerrierobject.Thespecialmethod__init__isthePythonconstructor. Withanunderstandingofobjectorientedprogrammingandclasses,let’snowlookathowthe__init__methodworkswithinaPythonprogram. TheImportanceofObjectsinPython Wedon’talwaysseeitwhenwewriteaprogram,butobjectsarecentraltothewayPythonworks.WhenwedeclareasimplevariableinPython,anobjectiscreatedinthebackground.Ifweexecutethefollowingbitofcode: breed="Doberman" Pythonusesthestrclassthatcontainspropertiesandmethods,exactlyliketheonesyoucreateinyourowncode,exceptit’sallhappeninginthebackground. HowDoesthe__init__MethodWork?  The__init__methodisthePythonequivalentoftheC++constructorinanobject-orientedapproach.The__init__ functioniscalledeverytimeanobjectiscreatedfromaclass.The__init__methodletstheclassinitializetheobject’sattributesandservesnootherpurpose.Itisonlyusedwithinclasses.  CreateaClass Let’sbeginbycreatingaclass: classDog: def__init__(self,dogBreed,dogEyeColor): self.breed=dogBreed self.eyeColor=dogEyeColor... First,wedeclaretheclassDogusingthekeywordclass.Weusethekeyworddeftodefineafunctionormethod,suchasthe__init__method.Asyoucansee,the__init__methodinitializestwoattributes:breedandeyeColor.  We’llnowseehowtopasstheseparameterswhendeclaringanobject.Thisiswhereweneedthekeywordselftobindtheobject’sattributestotheargumentsreceived. CreateanObject Nextwe’llcreateanobject,orinstance,oftheclassDog: ...Tomita=Dog("FoxTerrier","brown")... Whenwecreatetheobjecttomita(whichisthedog’sname),wefirstdefinetheclassfromwhichitiscreated(Dog).Wenextpassthearguments“FoxTerrier”and“brown,”whichcorrespondtotherespectiveparametersofthe__init__methodoftheclassDog. The__init__methodusesthekeywordselftoassignthevaluespassedasargumentstotheobjectattributesself.breedandself.eyeColor. AccessObjectAttributes ToaccessanattributeofyourbrandnewFoxTerrierobject,youcanusethedot(.)notationtogetthevalueyouneed.Aprintstatementhelpsusdemonstratehowthisworks: ...print("Thisdogisa",tomita.breed,"anditseyesare",tomita.eyeColor) Executingtheabovecodegivesusthefollowingresult: ThisdogisaFoxTerrieranditseyesarebrown Theprogramaccessedtomita’sattributesanddisplayedthemproperly. TheDefault__init__Constructor InPython,aconstructordoesnotnecessarilyneedparameterspassedtoit.Therecanbedefaultparameters.Aconstructorwithnomandatoryparametersiscalledadefaultconstructor.Let’srewriteourclasswithadefaultconstructor: classDog: def__init__(self,dogBreed="GermanShepherd",dogEyeColor="Brown"): self.breed=dogBreed self.eyeColor=dogEyeColor Ifauserdoesnotenteranyvalues,theconstructorwillassign“GermanShepherd”and“Brown”astheattributes. WecannowcreateaninstanceofDogwithoutspecifyinganyparameter:  tomita=Dog() Sincetherearenoargumentstopass,weuseemptyparenthesesaftertheclassname.Wecanstilldisplaytheobject’sattributes: print("Thisdogisa",tomita.breed,"anditseyesare",tomita.eyeColor) Thisgivesusthefollowingoutput: ThisdogisaGermanShepherdanditseyesareBrown Thissimplecodeworksperfectly. LearnToCodeWithUdacity The__init__methodisparamounttoPython’sobject-orientedprogramming..Inthisarticle,weexplainedtheroleofthe__init__methodwithinthecontextofOOPandclassdefinition.The__init__methodisoneofthenumerousspecialmethodsbuiltintoPython,andprogrammerscanuseitwithorwithoutparametersforeachclasstheycreate. Wanttoreallytakeyourcodingskillstothenextlevel?OurIntroductiontoProgrammingNanodegreeprogramisyournextstep.We’llteachyouthefoundationsofcodingandhaveyouthinkingandproblemsolvinglikeaprogrammer! CompleteCodeExample Example1: classDog: def__init__(self,dogBreed,dogEyeColor): self.breed=dogBreed self.eyeColor=dogEyeColor tomita=Dog("FoxTerrier","brown") print("Thisdogisa",tomita.breed,"andhiseyesare",tomita.eyeColor) Example2: classDog: def__init__(self): self.nbLegs=4 tomita=Dog() print("Thisdoghas",tomita.nbLegs,"legs") Example3: classDog: def__init__(self,dogBreed="GermanShepherd",dogEyeColor="brown"): self.breed=dogBreed self.eyeColor=dogEyeColor tomita=Dog() print("Thisdogisa",tomita.breed,"andhiseyesare",tomita.eyeColor) AlexeyKlochay ViewAllPostsbyAlexeyKlochay Search PopularNanodegrees ProgrammingforDataSciencewithPython DataScientistNanodegree Self-DrivingCarEngineer DataAnalystNanodegree AndroidBasicsNanodegree IntrotoProgrammingNanodegree AIforTrading PredictiveAnalyticsforBusinessNanodegree AIForBusinessLeaders DataStructures&Algorithms SchoolofArtificialIntelligence SchoolofCyberSecurity SchoolofDataScience SchoolofBusiness SchoolofAutonomousSystems SchoolofExecutiveLeadership SchoolofProgrammingandDevelopment RelatedArticles ReintroducingtheDeepLearningNanodegreeProgramfromUdacity UdacityisexcitedtoreintroduceanupdatetoaprograminourSchoolofArtificialIntelligence:the... 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