Python's self - Python Morsels

self is the first method of every Python class Articles Screencasts Exercises Courses Pastebin Gift / SignUp SignIn Watchasvideo 03:28 Showcaptions Autoplay Auto-expand Signintochangeyoursettings SignintoyourPythonMorselsaccounttosaveyourscreencastsettings. Don'thaveanaccountyet?Signuphere. WhenyoudefineaclassinPython,you'llseeselfeverywhere. Whatisselfandwhyisiteverywhere? APythonclasswithselfineachmethod ThebelowPointhasthreemethods:a__init__method,anis_originmethod,andamove_tomethod. classPoint: def__init__(self,x,y,z): self.move_to(x,y,z) defis_origin(self): returnself.x==self.y==self.z==0 defmove_to(self,x,y,z): self.x,self.y,self.z=x,y,z Wecanmakeaninstanceofthisclass,bycallingit. Wecanaccessattributesandcancallmethodsonthisclassinstance: >>>p=Point(1,2,3) >>>p.x 1 >>>p.is_origin() False >>> Doweneedthatselfargument? EachofthemethodsinourPointclassacceptsselfasitsfirstargument. Whatdoyouthinkwillhappen,ifwedeletethatselfargument? classPoint: def__init__(x,y,z): self.move_to(x,y,z) defis_origin(): returnself.x==self.y==self.z==0 defmove_to(x,y,z): self.x,self.y,self.z=x,y,z NowwhenwecallthePointclasstomakeanewPointobject,we'llseeanerror: >>>p=Point(1,2,3) Traceback(mostrecentcalllast): File"",line1,in TypeError:__init__()takes3positionalargumentsbut4weregiven >>> Theerrorsays__init__(ourinitializermethod)takesthreepositionalarguments,butfourweregiven. WeonlypassedthreeargumentsintoourPointclass;itgotfourargumentsbecauseselfwaspassedinasthefirstargument(beforethethreewespecified). Sowhetheryoulikeitornot,thefirstargumenttoeveryoneofyourmethodsisgoingtobeself,whichmeansweneedtocapturethisselfthingthat'spassedinasthefirstargument. Whatisself? Sowhatisself? Let'stemporarilychangeouris_originmethodheretoreturntheidofself: defis_origin(self): returnid(self) Python'sidfunctionreturnsanumberrepresentingthememorylocationofaparticularobject. Ifwecalltheis_originfunction,wegetanumber. >>>p=Point(1,2,3) >>>p.is_origin() 139775673938080 Ifwelookattheidofthepvariablewemade,we'regoingtogetthesamenumber: >>>id(p) 139775673938080 ThatvariableppointstoaPointobject(remembervariablesarepointersinPython). Thatselfvariableinourmethodcallpointstothesameexactobject. Soselfisreallyjustavariablethatpointstotheinstanceofourclassthatwe'recurrentlyworkingwith. Butwhatdoesselfmean?Couldwerenameit? Whatifwetakeselfeverywhereinthecodeandchangeittothis? classPoint: def__init__(this,x,y,z): this.move_to(x,y,z) defis_origin(this): returnthis.x==this.y==this.z==0 defmove_to(this,x,y,z): this.x,this.y,this.z=x,y,z Wouldourcodestillwork? IfwemakeanewPointobjectagain,we'llseethatweeverythingworksasitdidbefore:wecanstillaccessattributesandwecanstillcallmethods: >>>p=Point(1,2,3) >>>p.x 1 >>>p.is_origin() False FromPython'sperspective,itdoesn'tactuallymatter,whatyoucallself. Youjusthavetoacceptthattheinstanceofyourclasswillbepassedinasthefirstargument. Theselfvariableisjustaverystrongconvention,youshouldcallitself(otherwiseotherPythonprogrammerswillbeconfusedwhenreadingyourcode)butyou'reallowedtocallitsomethingelse. selfisthefirstmethodofeveryPythonclass WhenPythoncallsamethodinyourclass,itwillpassintheactualinstanceofthatclassthatyou'reworkingwithasthefirstargument. Someprogramminglanguagesusethewordthistorepresentthatinstance,butinPythonweusethewordself. WhenyoudefineaclassinPython,everymethodthatyoudefine,mustacceptthatinstanceasitsfirstargument(calledselfbyconvention). Theselfvariablepointstotheinstanceoftheclassthatyou'reworkingwith. Series:Classes Classesareawaytobundlefunctionalityandstatetogether. Theterms"type"and"class"areinterchangeable:list,dict,tuple,int,str,set,andboolareallclasses. You'llcertainlyusequiteafewclassesinPython(remembertypesareclasses)butyoumaynotneedtocreateyourownoften. TotrackyourprogressonthisPythonMorselstopictrail,signinorsignup. 0% Whatisaclass? 04:34 Classesareeverywhere 03:14 Python'sself 03:28 __init__inPython 03:09 DocstringsinPython 04:43 Inheritingoneclassfromanother 04:08 AttributesareeverywhereinPython 02:30 Methodsarejustfunctionsattachedtoclasses 05:02 Whereareattributesstored? 03:07 Howattributelookupsandassignmentswork 03:35 WheredoesPythonlookformethods? 03:22 Restrictingclassattributeswith__slots__ 04:17 Classmethods 03:47 Staticmethods 02:44 WhatcomesafterIntrotoPython? IntrotoPythoncoursesoftenskipoversomefundamentalPythonconcepts. SignupbelowandI'llexplainconceptsthatnewPythonprogrammersoftenoverlook. Website SignupforPythonConceptsBeyondtheBasics ✕ ↑ ConceptsBeyondIntrotoPython IntrotoPythoncoursesoftenskipoversomefundamentalPythonconcepts. SignupbelowandI'llshareideasnewPythonistasoftenoverlook. Website Watchasvideo 03:28 TableofContents NextUp 03:09 __init__inPython The__init__methodisusedtoinitializeaclass.Theinitializermethodacceptsself(theclassinstance)alongwithanyargumentstheclassacceptsandthenperformsinitializationsteps.