Python classmethod() - Programiz

A class method is a method that is bound to a class rather than its object. It doesn't require creation of a class instance, much like staticmethod. The ... CourseIndex ExploreProgramiz Python JavaScript SQL C C++ Java Kotlin Swift C# DSA LearnPythonpractically andGetCertified. ENROLL PopularTutorials GettingStartedWithPython PythonifStatement whileLoopinPython PythonLists DictionariesinPython StartLearningPython PopularExamples Addtwonumbers Checkprimenumber Findthefactorialofanumber PrinttheFibonaccisequence Checkleapyear ExplorePythonExamples ReferenceMaterials Built-inFunctions ListMethods DictionaryMethods StringMethods Viewall LearningPaths Challenges LearnPythonInteractively TryforFree Courses BecomeaPythonMaster BecomeaCMaster BecomeaJavaMaster ViewallCourses Python JavaScript SQL C C++ Java Kotlin Swift C# DSA LearnPythonpractically andGetCertified. ENROLLFORFREE! 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Theclassmethod()methodreturnsaclassmethodforthegivenfunction. Example classStudent: marks=0 defcompute_marks(self,obtained_marks): marks=obtained_marks print('ObtainedMarks:',marks) #convertcompute_marks()toclassmethod Student.print_marks=classmethod(Student.compute_marks) Student.print_marks(88) #Output:ObtainedMarks:88 classmethod()Syntax Thesyntaxofclassmethod()methodis: classmethod(function) classmethod()isconsideredun-PythonicsoinnewerPythonversions,youcanusethe@classmethoddecoratorforclassmethoddefinition. Thesyntaxis: @classmethod deffunc(cls,args...) classmethod()Parameters classmethod()methodtakesasingleparameter: function-Functionthatneedstobeconvertedintoaclassmethod classmethod()ReturnValue classmethod()methodreturnsaclassmethodforthegivenfunction. Whatisaclassmethod? Aclassmethodisamethodthatisboundtoaclassratherthanitsobject.Itdoesn'trequirecreationofaclassinstance,muchlikestaticmethod. Thedifferencebetweenastaticmethodandaclassmethodis: Staticmethodknowsnothingabouttheclassandjustdealswiththeparameters Classmethodworkswiththeclasssinceitsparameterisalwaystheclassitself. Theclassmethodcanbecalledbothbytheclassanditsobject. Class.classmethod() Oreven Class().classmethod() Butnomatterwhat,theclassmethodisalwaysattachedtoaclasswiththefirstargumentastheclassitselfcls. defclassMethod(cls,args...) Example1:Createclassmethodusingclassmethod() classPerson: age=25 defprintAge(cls): print('Theageis:',cls.age) #createprintAgeclassmethod Person.printAge=classmethod(Person.printAge) Person.printAge() Output Theageis:25 Here,wehaveaclassPerson,withamembervariableageassignedto25. WealsohaveafunctionprintAgethattakesasingleparameterclsandnotselfweusuallytake. clsacceptstheclassPersonasaparameterratherthanPerson'sobject/instance. Now,wepassthemethodPerson.printAgeasanargumenttothefunctionclassmethod.Thisconvertsthemethodtoaclassmethodsothatitacceptsthefirstparameterasaclass(i.e.Person). Inthefinalline,wecallprintAgewithoutcreatingaPersonobjectlikewedoforstaticmethods.Thisprintstheclassvariableage. Whendoyouusetheclassmethod? 1.Factorymethods Factorymethodsarethosemethodsthatreturnaclassobject(likeconstructor)fordifferentusecases. ItissimilartofunctionoverloadinginC++.Since,Pythondoesn'thaveanythingassuch,classmethodsandstaticmethodsareused. Example2:Createfactorymethodusingclassmethod fromdatetimeimportdate #randomPerson classPerson: def__init__(self,name,age): self.name=name self.age=age @classmethod deffromBirthYear(cls,name,birthYear): returncls(name,date.today().year-birthYear) defdisplay(self): print(self.name+"'sageis:"+str(self.age)) person=Person('Adam',19) person.display() person1=Person.fromBirthYear('John',1985) person1.display() Output Adam'sageis:19 John'sageis:31 Here,wehavetwoclassinstancecreator,aconstructorandafromBirthYearmethod. Theconstructortakesnormalparametersnameandage.While,fromBirthYeartakesclass,nameandbirthYear,calculatesthecurrentagebysubtractingitwiththecurrentyearandreturnstheclassinstance. ThefromBirthYearmethodtakesPersonclass(notPersonobject)asthefirstparameterclsandreturnstheconstructorbycallingcls(name,date.today().year-birthYear),whichisequivalenttoPerson(name,date.today().year-birthYear) Beforethemethod,wesee@classmethod.ThisiscalledadecoratorforconvertingfromBirthYeartoaclassmethodasclassmethod(). 2.Correctinstancecreationininheritance Wheneveryouderiveaclassfromimplementingafactorymethodasaclassmethod,itensurescorrectinstancecreationofthederivedclass. Youcancreateastaticmethodfortheaboveexamplebuttheobjectitcreates,willalwaysbehardcodedasBaseclass. But,whenyouuseaclassmethod,itcreatesthecorrectinstanceofthederivedclass. Example3:Howtheclassmethodworksfortheinheritance? fromdatetimeimportdate #randomPerson classPerson: def__init__(self,name,age): self.name=name self.age=age @staticmethod deffromFathersAge(name,fatherAge,fatherPersonAgeDiff): returnPerson(name,date.today().year-fatherAge+fatherPersonAgeDiff) @classmethod deffromBirthYear(cls,name,birthYear): returncls(name,date.today().year-birthYear) defdisplay(self): print(self.name+"'sageis:"+str(self.age)) classMan(Person): sex='Male' man=Man.fromBirthYear('John',1985) print(isinstance(man,Man)) man1=Man.fromFathersAge('John',1965,20) print(isinstance(man1,Man)) Output True False Here,usingastaticmethodtocreateaclassinstancewantsustohardcodetheinstancetypeduringcreation. ThisclearlycausesaproblemwheninheritingPersontoMan. fromFathersAgemethoddoesn'treturnaManobjectbutitsbaseclassPerson'sobject. ThisviolatestheOOPparadigm.UsingaclassmethodasfromBirthYearcanensuretheOOP-nessofthecodesinceittakesthefirstparameterastheclassitselfandcallsitsfactorymethod. PreviousTutorial: Pythoncompile() NextTutorial: Pythoncomplex() Shareon: Didyoufindthisarticlehelpful? Sorryaboutthat. Howcanweimproveit? Feedback* Leavethisfieldblank PythonReferencesPythonLibraryPythonstaticmethod()PythonLibraryPythonsetattr()PythonLibraryPythongetattr()PythonLibraryPythonproperty() TryPROforFREE LearnPythonInteractively