2023学年完整公开课版74Openingandclosingoffiles

Openingandclosingoffiles2learningtasksOpenthefilecorrectlyusingPythonsyntax.3KnowledgeobjectivesLearnhowtoopenandclosefilesinPythonUnderstandtheroleofclosingfiles01CapabilityobjectivesAbilitytoopenandclosefilesAbilitytoreadfileseasily02Learningobjectives4FileoperationconceptPythonprovidesalargenumberoffunctionsandmethodstooperateonfiles.Ingeneral，youcanusethefileobjecttodomostofthefunctions.5FileoperationmethodOpenafilebeforeworkingonit.Python'sbuilt-inopen()functionopensafileandcreatesafileobject.Throughthisobject，wecancallrelatedmethodstoreadandwritefiles.6OpenfileOpenfunctionSyntax:open(name[，mode[，buffering]])Parameter:Name:thenameofthefiletoaccess(string).Mode:fileopenmode:readonly，write，append，etc.Optionalparameter，read-onlybydefault.Buffering:filebuffer.0:nobuffer，dataiswrittendirectlytotheharddisk.1:Withbuffer，thedataiswrittentothememoryfirst.Whenusingtheflushorclosefunction，thedatawillbeupdatedtotheharddisk.Greaterthan1:indicatesthesizeofthebufferinbytes.Negativevalue(default-1):thebuffersizeisthesystemdefault.Returnvalue:fileobject.7ClosefilecauseAfterthefileoperation，closethefile.Ifnot，waituntilthegarbagecollectiontoautomaticallyreleasetheresources.Butthetimingofgarbagecollectionisuncertainanduncontrollable，whichmayleadtoaseriesofresourceproblemsandleadtoerrors.Inaddition，datamaybelostduetobuffering.8ClosefileClose

methodTheclose()methodisusedtocloseanopenfile.Theclosedfilecannolongerbereadorwritten，otherwisethevalueerrorerrorwillbetriggered.Whenafileobjectisreferencedtoanotherfile，pythonautomaticallyclosesthepreviousfileobject.Usingtheclose()methodtoclosefilesisagoodhabit.Syntax:fileObject.close();Noparameternoreturn.9OpenandClosefilewith…as…grammerInPython，youcanusewithopen()asvar_Name:syntaxsecurityopenfile.Inthisway，theuseofwithkeywordwillautomaticallycleanup(close())whenexitingthefileoperation.Ifyouneedtocleanupbeforethat，youcanalsodisplaythecalltoclose()method.10OpenandClosefileexample111OpenandClosefileexam