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Legbprinciple2learningtasksUnderstandtheprocessofvariablenameresolutionunderthelegbprinciple.3KnowledgeobjectivesUnderstandtheconceptofscopeUnderstandingthelegbprinciplesinPython01CapabilityobjectivesBeabletousethelegbprincipletosolvepracticalproblems02Learningobjectives4VariabledefinitionprocessWhenvariablesareusedingeneralhigh-levellanguages,therearefourproceduresasfollows.Ofcourse,therewillbedifferencesindifferentlanguages.1.Declarevariable:lettheeditorknowtheexistenceofthisvariable;2.Definevariables:allocatememoryspaceforvariablesofdifferentdatatypes;3.Initialization:assignavalueandfillintheallocatedmemoryspace;4.Reference:callmemoryobject(memorydata)byreferenceobject(variablename).5ScopedefinitionWhencreating,changing,andlookingupvariablenamesinPythonprograms,theyarealldoneinaspacewherevariablenamesaresaved.Wecallitnamespace,alsoknownasscope.Python'sscopeisstatic,andthelocationwherethevariablenameisassignedinthesourcecodedeterminestherangethatthevariablecanbeaccessed.Thatis,thescopeofPythonvariablesisdeterminedbythelocationofthevariablesinthesourcecode.6ScopetypeInPython,itisnotstrictlyrequiredtodeclareavariableinadvancewhenusingit,butbeforeusingit,itmustbeboundtoamemoryobject(defined,assigned);thisbindingofvariablenameswillintroducenewvariablesintothecurrentscope,andmaskvariableswiththesamenameintheouterscope.InPython,therearefourtypesofscopes.7ScopetypeL(local)localscopeLocalvariable:includedinthestatementblockdefinedbydefkeyword,thatis,thevariabledefinedinthefunction.Wheneverafunctioniscalled,anewlocalscopeiscreated.E(embedding)nestedscopeEisalsoincludedinthedefkeyword.ThedifferencebetweenEandlisthatforafunction,listhelocalscopedefinedwithinthefunction,whileeistheupperlevelofthefunction,thatis,thelocalscopeoftheparentfunction.8ScopetypeG(global)globalscopeThatis,thevariablesdefinedinthemodulelevel,eachmoduleisaglobalscope.Fromtheexternalpointofview,theglobalvariableofamoduleistheattributeofamoduleobject.Note:thescopeoftheglobalscopeislimitedtoasinglemodulefileB(builtin)builtinscopeVariablesdefinedinfixedmodulesinthesystem,suchaspredefinedin__builtins__Print,input,hemodule.9ScopefindPriorityofsearchvariablename:localscope>nestedscope>globalscope>built-inscope.10LegbprincipleconceptWhenanunidentifiedvariablenameisusedinafunction,pythonsearchesfourscopesinorderofprioritytodeterminethemeaningofthevariablename.Thelocalscope(L)issearchedfirst,followedbythenestedscope(E)ofdeforlambdafunctionsinthepreviousnestingstructure,followedbytheglobalscope(g),andfinallythebuilt-inscope(b).Accordingtothissearchprinciple,stopatthefirstplace.Ifnotfound,aNameErrorexceptionisthrown.11Legbprincipleexample112Legbprincipleexample213Taskimplem

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