2023學(xué)年完整公開課版1ThewayofPythonprogramworks

ThewayofPythonprogramworks2LearningtasksLearnhowtorunPythonprograms3TheknowledgeobjectiveFromtwowaystounderstandhowaPythonprogramworksFamiliarwiththeroleofthePythonvirtualmachineoneAbilityaimLanguagetypesthatcanexplainPythoncanexplainhowaPythonprogramrunstwolearningtarget4InterpretedlanguagesandCompiledlanguageComputerLanguageComputersarenotcapableofrecognizinghigh-levellanguages,Sowhenwerunahigh-levellanguageprogram,A"translationmachine"isneededtoconvertahigh-levellanguageintomachinelanguagethatacomputercanunderstand.Thisprocessfallsintotwocategories,Thefirstiscompilation,thesecondisinterpretation.However,Withtheriseofvirtualmachine-basedlanguagessuchasJava,Wecannotdividelanguagespurelyintointerpretedandcompiled.5InterpretedlanguagesandCompiledlanguageComputerLanguageCompiledlanguagesprecedeprogramexecution,first,acompilerisusedtocompiletheprogram,translateaprogramintomachinelanguage.Translationisnolongerrequiredatruntime,justexecuteit.ThemosttypicalexampleistheClanguage.Interpretedlanguageshavenocompilationprocess,whiletheprogramisrunning,theprogramisinterpretedlinebylinethroughtheinterpreter,thenjustrunit,ThemosttypicalexampleisRuby.Javalanguageisfirstandforemostbycompilerscompiledintobytecodefiles,theninterpretedasamachinefilethroughtheinterpreteratruntime.SoJavaisacompiledandinterpretedlanguage.6InterpretedlanguagesandCompiledlanguagePythonlanguagetypePythonisalsoavirtualmachine-basedlanguage.Whentypingpython*.pyonthecommandline,isactuallyactivatedthePython"theinterpreter".Butbeforethe"explanation",thefirstthingyoudoisthesameasJava,itiscompiled.SoweshoulddescribePythonthisway:Pythonisafirstcompiledandtheninterpretedoflanguage.7TherunningofaPythonprogramThePythoninterpreterTheinterpreterisaprogramthatmakesotherprogramsrun.WhenyouwriteaPythonprogram,ThePythoninterpreterwillreadtheprogram,executethecommandstherein,drawtheconclusion.Infact,Theinterpreteristhesoftwarelogiclayerbetweenthecodeandthemachineiscomputerhardware.whenthePythonpackageisinstalledonthemachine,italreadyincludessomeminimalcomponents:ainterpreterandsupportedlibraries.Itdependsontheusage,thePythoninterpretermaytakedifferentforms,butinwhateverform,thePythoncodeyouwritemustrunintheinterpreter.8TherunningofaPythonprogramProgrammerperspectiveInitssimplestform,aPythonprogramissimplyatextfilecontainingPythoncode.Fromtheprogrammerisperspective,wesaveourPythoncodeina.pyfile,executethisfile,standardoutputwillreturnustheresult.Thatis,youentercodeintoafile,executethecodeintheinterpreter.9TherunningofaPythonprogramPythonPerspectivePython'straditionalrunningexecutionmode:theinputsourcecodeisconvertedtobytecode,whichisthenruninthePVM.Codeisautomaticallycompiledandinterpreted.10TherunningofaPythonprogramPythonPerspective1、bytecodecompilationWhentheprogramisexecuted,Pythoninternallycompilesthesourcecodeintobytecodeform.Compilationisasimpletranslationstep.IfthePythonprocesshaswritepermissiononthemachine,itsavesthebytecodeoftheprogramasafilewiththeextension.pyc.Atthenextrun,ifthesourcecodehasnotbeenmodifiedsincethelastsavedbytecode,Pythonwillskipthecompilationandloadthe.pycfiledirectly,increasingthestartupspeed.IfPythoncannotwritethebytecodeonthemachine,theprogramwillstillwork,andthebytecodewillbegeneratedinmemoryanddiscardedattheendoftheprogram.11TherunningofaPythonprogramPythonPerspective2、Pythonvirtualmachine(PVM)Oncetheprogramhasbeencompiledintobytecode(orbytecodeloadedfromanexisting.pycfile),thebytecodeissenttothePVMforexecution.PVMisnotastandaloneprogramanddoesnotrequireinstallation.PVMisalargeloopthatiterativelyrunsbytecodeinstructions,completingoneoperationafteranother.PVMisthePythonrunningengine,representedaspartofthePythonsystem,anditisthe