Polymorphism in Python - PYnative

Polymorphism in Python is the ability of an object to take many forms. In simple words, polymorphism allows us to perform the same action in ... Home»Python»PythonObject-OrientedProgramming(OOP)»PolymorphisminPython Object-OrientedProgramming(OOP)hasfouressentialcharacteristics:abstraction,encapsulation,inheritance,andpolymorphism. ThislessonwillcoverwhatpolymorphismisandhowtoimplementtheminPython.Also,you’lllearnhowtoimplementpolymorphismusingfunctionoverloading,methodoverriding,andoperatoroverloading. TableofcontentsWhatisPolymorphisminPython?PolymorphisminBuilt-infunctionlen()PolymorphismWithInheritanceExample:MethodOverridingOverrrideBuilt-inFunctionsPolymorphismInClassmethodsPolymorphismwithFunctionandObjectsPolymorphismInBuilt-inMethodsMethodOverloadingOperatorOverloadinginPythonOverloading+operatorforcustomobjectsOverloadingthe*OperatorMagicMethods WhatisPolymorphisminPython? PolymorphisminPythonistheabilityofanobjecttotakemanyforms.Insimplewords,polymorphismallowsustoperformthesameactioninmanydifferentways. Forexample,Jessaactsasanemployeewhensheisattheoffice.However,whensheisathome,sheactslikeawife.Also,sherepresentsherselfdifferentlyindifferentplaces.Therefore,thesamepersontakesdifferentformsasperthesituation. Apersontakesdifferentforms Inpolymorphism,amethodcanprocessobjectsdifferentlydependingontheclasstypeordatatype.Let’sseesimpleexamplestounderstanditbetter. PolymorphisminBuilt-infunctionlen() Thebuilt-infunctionlen()calculatesthelengthofanobjectdependinguponitstype.Ifanobjectisastring,itreturnsthecountofcharacters,andIfanobjectisalist,itreturnsthecountofitemsinalist. Thelen()methodtreatsanobjectasperitsclasstype. Example: students=['Emma','Jessa','Kelly'] school='ABCSchool' #calculatecount print(len(students)) print(len(school)) Output 3 10 Polymorphiclen()function PolymorphismWithInheritance Polymorphismismainlyusedwithinheritance.Ininheritance,childclassinheritstheattributesandmethodsofaparentclass.Theexistingclassiscalledabaseclassorparentclass,andthenewclassiscalledasubclassorchildclassorderivedclass. Usingmethodoverridingpolymorphismallowsustodefinesmethodsinthechildclassthathavethesamenameasthemethodsintheparentclass.Thisprocessofre-implementingtheinheritedmethodinthechildclassisknownasMethodOverriding. Advantageofmethodoverriding Itiseffectivewhenwewanttoextendthefunctionalitybyalteringtheinheritedmethod.Orthemethodinheritedfromtheparentclassdoesn’tfulfilltheneedofachildclass,soweneedtore-implementthesamemethodinthechildclassinadifferentway.Methodoverridingisusefulwhenaparentclasshasmultiplechildclasses,andoneofthatchildclasswantstoredefinethemethod.Theotherchildclassescanusetheparentclassmethod.Duetothis,wedon’tneedtomodificationtheparentclasscode Inpolymorphism,Pythonfirstcheckstheobject’sclasstypeandexecutestheappropriatemethodwhenwecallthemethod.Forexample,IfyoucreatetheCarobject,thenPythoncallsthespeed()methodfromaCarclass. Let’sseehowitworkswiththehelpofanexample. Example:MethodOverriding Inthisexample,wehaveavehicleclassasaparentanda‘Car’and‘Truck’asitssub-class.Buteachvehiclecanhaveadifferentseatingcapacity,speed,etc.,sowecanhavethesameinstancemethodnameineachclassbutwithadifferentimplementation.Usingthiscodecanbeextendedandeasilymaintainedovertime. PolymorphismwithInheritance classVehicle: def__init__(self,name,color,price): self.name=name self.color=color self.price=price defshow(self): print('Details:',self.name,self.color,self.price) defmax_speed(self): print('Vehiclemaxspeedis150') defchange_gear(self): print('Vehiclechange6gear') #inheritfromvehicleclass classCar(Vehicle): defmax_speed(self): print('Carmaxspeedis240') defchange_gear(self): print('Carchange7gear') #CarObject car=Car('Carx1','Red',20000) car.show() #callsmethodsfromCarclass car.max_speed() car.change_gear() #VehicleObject vehicle=Vehicle('Truckx1','white',75000) vehicle.show() #callsmethodfromaVehicleclass vehicle.max_speed() vehicle.change_gear() Output: Details:Carx1Red20000 Carmaxspeedis240 Carchange7gear Details:Truckx1white75000 Vehiclemaxspeedis150 Vehiclechange6gear Asyoucansee,duetopolymorphism,thePythoninterpreterrecognizesthatthemax_speed()andchange_gear()methodsareoverriddenforthecarobject.So,itusestheonedefinedinthechildclass(Car) Ontheotherhand,theshow()methodisn’toverriddenintheCarclass,soitisusedfromtheVehicleclass. OverrrideBuilt-inFunctions InPython,wecanchangethedefaultbehaviorofthebuilt-infunctions.Forexample,wecanchangeorextendthebuilt-infunctionssuchaslen(),abs(),ordivmod()byredefiningtheminourclass.Let’sseetheexample. Example Inthisexample,wewillredefinethefunctionlen() classShopping: def__init__(self,basket,buyer): self.basket=list(basket) self.buyer=buyer def__len__(self): print('Redefinelength') count=len(self.basket) #counttotalitemsinadifferentway #pairofshoesandshir+pant returncount*2 shopping=Shopping(['Shoes','dress'],'Jessa') print(len(shopping)) Output Redefinelength 4 PolymorphismInClassmethods Polymorphismwithclassmethodsisusefulwhenwegroupdifferentobjectshavingthesamemethod.wecanaddthemtoalistoratuple,andwedon’tneedtochecktheobjecttypebeforecallingtheirmethods.Instead,Pythonwillcheckobjecttypeatruntimeandcallthecorrectmethod.Thus,wecancallthemethodswithoutbeingconcernedaboutwhichclasstypeeachobjectis.Weassumethatthesemethodsexistineachclass. Pythonallowsdifferentclassestohavemethodswiththesamename. Let’sdesignadifferentclassinthesamewaybyaddingthesamemethodsintwoormoreclasses.Next,createanobjectofeachclassNext,addallobjectsinatuple.Intheend,iteratethetupleusingaforloopandcallmethodsofaobjectwithoutcheckingitsclass. Example Inthebelowexample,fuel_type()andmax_speed()aretheinstancemethodscreatedinbothclasses. classFerrari: deffuel_type(self): print("Petrol") defmax_speed(self): print("Maxspeed350") classBMW: deffuel_type(self): print("Diesel") defmax_speed(self): print("Maxspeedis240") ferrari=Ferrari() bmw=BMW() #iterateobjectsofsametype forcarin(ferrari,bmw): #callmethodswithoutcheckingclassofobject car.fuel_type() car.max_speed() Output Petrol Maxspeed350 Diesel Maxspeedis240 Asyoucansee,wehavecreatedtwoclassesFerrariandBMW.Theyhavethesameinstancemethodnamesfuel_type()andmax_speed().However,wehavenotlinkedboththeclassesnorhaveweusedinheritance. Wepackedtwodifferentobjectsintoatupleanditeratethroughitusingacarvariable.ItispossibleduetopolymorphismbecausewehaveaddedthesamemethodinbothclassesPythonfirstcheckstheobject’sclasstypeandexecutesthemethodpresentinitsclass. PolymorphismwithFunctionandObjects Wecancreatepolymorphismwithafunctionthatcantakeanyobjectasaparameterandexecuteitsmethodwithoutcheckingitsclasstype.Usingthis,wecancallobjectactionsusingthesamefunctioninsteadofrepeatingmethodcalls. Example classFerrari: deffuel_type(self): print("Petrol") defmax_speed(self): print("Maxspeed350") classBMW: deffuel_type(self): print("Diesel") defmax_speed(self): print("Maxspeedis240") #normalfunction defcar_details(obj): obj.fuel_type() obj.max_speed() ferrari=Ferrari() bmw=BMW() car_details(ferrari) car_details(bmw) Output Petrol Maxspeed350 Diesel Maxspeedis240 PolymorphismInBuilt-inMethods ThewordpolymorphismistakenfromtheGreekwordspoly(many)andmorphism(forms).Itmeansamethodcanprocessobjectsdifferentlydependingontheclasstypeordatatype. Thebuilt-infunctionreversed(obj)returnstheiterablebyreversingthegivenobject.Forexample,ifyoupassastringtoit,itwillreverseit.Butifyoupassalistofstringstoit,itwillreturntheiterablebyreversingtheorderofelements(itwillnotreversetheindividualstring). Letusseehowabuilt-inmethodprocessobjectshavingdifferentdatatypes. Example: students=['Emma','Jessa','Kelly'] school='ABCSchool' print('Reversestring') foriinreversed('PYnative'): print(i,end='') print('\nReverselist') foriinreversed(['Emma','Jessa','Kelly']): print(i,end='') Output: Reversestring evitanYP Reverselist KellyJessaEmma MethodOverloading Theprocessofcallingthesamemethodwithdifferentparametersisknownasmethodoverloading.Pythondoesnotsupportmethodoverloading.Pythonconsidersonlythelatestdefinedmethodevenifyouoverloadthemethod.PythonwillraiseaTypeErrorifyouoverloadthemethod. Example defaddition(a,b): c=a+b print(c) defaddition(a,b,c): d=a+b+c print(d) #thebelowlineshowsanerror #addition(4,5) #Thislinewillcallthesecondproductmethod addition(3,7,5) Toovercometheaboveproblem,wecanusedifferentwaystoachievethemethodoverloading.InPython,tooverloadtheclassmethod,weneedtowritethemethod’slogicsothatdifferentcodeexecutesinsidethefunctiondependingontheparameterpasses. Forexample,thebuilt-infunctionrange()takesthreeparametersandproducedifferentresultdependinguponthenumberofparameterspassedtoit. Example: foriinrange(5):print(i,end=',') print() foriinrange(5,10):print(i,end=',') print() foriinrange(2,12,2):print(i,end=',') Output: 0,1,2,3,4, 5,6,7,8,9, 2,4,6,8,10, Let’sassumewehaveanarea()methodtocalculatetheareaofasquareandrectangle.Themethodwillcalculatetheareadependinguponthenumberofparameterspassedtoit. Ifoneparameterispassed,thentheareaofasquareiscalculatedIftwoparametersarepassed,thentheareaofarectangleiscalculated. Example:User-definedpolymorphicmethod classShape: #functionwithtwodefaultparameters defarea(self,a,b=0): ifb>0: print('AreaofRectangleis:',a*b) else: print('AreaofSquareis:',a**2) square=Shape() square.area(5) rectangle=Shape() rectangle.area(5,3) Output: AreaofSquareis:25 AreaofRectangleis:15 OperatorOverloadinginPython Operatoroverloadingmeanschangingthedefaultbehaviorofanoperatordependingontheoperands(values)thatweuse.Inotherwords,wecanusethesameoperatorformultiplepurposes. Forexample,the+operatorwillperformanarithmeticadditionoperationwhenusedwithnumbers.Likewise,itwillperformconcatenationwhenusedwithstrings. Theoperator + isusedtocarryoutdifferentoperationsfordistinctdatatypes.ThisisoneofthemostsimpleoccurrencesofpolymorphisminPython. Example: #add2numbers print(100+200) #concatenatetwostrings print('Jess'+'Roy') #mergertwolist print([10,20,30]+['jessa','emma','kelly']) Output: 300 JessRoy [10,20,30,'jessa','emma','kelly'] Overloading+operatorforcustomobjects Supposewehavetwoobjects,andwewanttoaddthesetwoobjectswithabinary+operator.However,itwillthrowanerrorifweperformadditionbecausethecompilerdoesn’taddtwoobjects.Seethefollowingexampleformoredetails. Example: classBook: def__init__(self,pages): self.pages=pages #creatingtwoobjects b1=Book(400) b2=Book(300) #addtwoobjects print(b1+b2) Output TypeError:unsupportedoperandtype(s)for+:'Book'and'Book' Wecanoverload+operatortoworkwithcustomobjectsalso.Pythonprovidessomespecialormagicfunctionthatisautomaticallyinvokedwhenassociatedwiththatparticularoperator. Forexample,whenweusethe+operator,themagicmethod__add__()isautomaticallyinvoked.Internally+operatorisimplementedbyusing__add__()method.Wehavetooverridethismethodinourclassifyouwanttoaddtwocustomobjects. Example: classBook: def__init__(self,pages): self.pages=pages #Overloading+operatorwithmagicmethod def__add__(self,other): returnself.pages+other.pages b1=Book(400) b2=Book(300) print("Totalnumberofpages:",b1+b2) Output Totalnumberofpages:700 Overloadingthe*Operator The*operatorisusedtoperformthemultiplication.Let’sseehowtooverloadittocalculatethesalaryofanemployeeforaspecificperiod.Internally*operatorisimplementedbyusingthe__mul__()method. Example: classEmployee: def__init__(self,name,salary): self.name=name self.salary=salary def__mul__(self,timesheet): print('Workedfor',timesheet.days,'days') #calculatesalary returnself.salary*timesheet.days classTimeSheet: def__init__(self,name,days): self.name=name self.days=days emp=Employee("Jessa",800) timesheet=TimeSheet("Jessa",50) print("salaryis:",emp*timesheet) Output Wrokedfor50days salaryis:40000 MagicMethods InPython,therearedifferentmagicmethodsavailabletoperformoverloadingoperations.Thebelowtableshowsthemagicmethodsnamestooverloadthemathematicaloperator,assignmentoperator,andrelationaloperatorsinPython. OperatorNameSymbolMagicmethodAddition+__add__(self,other)Subtraction-__sub__(self,other)Multiplication*__mul__(self,other)Division/__div__(self,other)FloorDivision//__floordiv__(self,other)Modulus%__mod__(self,other)Power**__pow__(self,other)Increment+=__iadd__(self,other)Decrement-=__isub__(self,other)Product*=__imul__(self,other)Division/+__idiv__(self,other)Modulus%=__imod__(self,other)Power**=__ipow__(self,other)Lessthan<__lt__>__gt__(self,other)Lessthanorequalto<=__le__(self,other)Greaterthanorequalto>=__ge__(self,other)Equalto==__eq__(self,other)Notequal!=__ne__(self,other)magicmethods Didyoufindthispagehelpful?Letothersknowaboutit.SharinghelpsmecontinuetocreatefreePythonresources. TweetF sharein shareP Pin AboutVishal FounderofPYnative.comIamaPythondeveloperandIlovetowritearticlestohelpdevelopers.FollowmeonTwitter.AllthebestforyourfuturePythonendeavors! 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