《Python語言程序設計》課件-第六章（中英文課件）

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Python語言程序設計《字典的定義》PythonLanguageProgrammingDictionaryDefinitions同現實中的字典相似，Python的字典利用”Key－Value”機制對存入字典的數據進行快速查找定位。案例字典的定義Similartothedictionaryinreality,Python'sdictionaryusesthe"KeyValue"mechanismtoquicklysearchandlocatethedatastoredinthedictionary.Casedictionarydefinitions案例字典的定義dict1={'張三':25,'李四':16,'王五':40}d={key1:value1,key2:value2}【例】一個簡單的字典實例字典注意事項：（1）鍵必須是唯一的，但值可以不唯一。（2）值可以取任何數據類型，但鍵必須是不可變的，如字符串、數字或元組。（3）字典的鍵值是“只讀”的，所以不能對鍵和值分別進行初始化。鍵用列表類型可以嗎？Dict1={'ZhangSan':25,'LiSi':16,'WangWu':40}d={key1:value1,key2:value2}[Example]AsimpleexampleofadictionarythatDictionaryNotes.(1)Thekeymustbeunique,butthevaluemaynotbeunique.(2)Thevaluecantakeanydatatype,butthekeymustbeimmutable,suchasastring,numberortuple.(3)Thekeysandvaluesofthedictionaryare"read-only",sothekeysandvaluescannotbeinitializedseparately.Isitokaytousealisttypeforkeys?Casedictionarydefinitions案例字典的定義dic={}dic.keys=(1,2,3,4,5,6)dic.values=("a","b","c","d","e","f")【例】值是只讀的，不可以修改AttributeError:'dict'objectattribute'keys'isread-onlyAttributeError:'dic'objectattribute'values'isread-onlydic={}dic.keys=(1,2,3,4,5,6)dic.values=("a","b","c","d","e","f")[Example]Thevalueisread-onlyandcannotbemodifiedAttributeError:'dict'objectattribute'keys'isread-onlyAttributeError:'dic'objectattribute'values'isread-onlyCasedictionarydefinitions問題1:鍵必須是唯一還是不唯一的？唯一的問題2:字典中的Value值可以重復嗎？提問可以Question1:Dokeyshavetobeuniqueornon-unique?TheoneandonlyQuestion2:Canthevalueinthedictionaryberepeated?AskaquestionYes,youcan問題3:字典中的鍵用列表類型可以嗎？提問值可以取任何數據類型，但鍵必須是不可變的，如字符串、數字或元組Question3:Isitoktousealisttypeforkeysinadictionary?Thevaluecantakeanydatatype,butthekeymustbeimmutable,suchasastring,number,ortupleAskaquestionPython語言程序設計《訪問字典里的值》PythonLanguageProgrammingAccesstoDictionaryValues案例訪問字典里的值dict={'Name':'DerisWeng','Age':7,'Class':'First'}print("dict['Name']:",dict['Name'])print("dict['Age']:",dict['Age'])訪問字典中的值可以通過dict[Key]的方式，即把相應的鍵放到方括弧[]中進行訪問。【例】通過直接引用訪問字典中的值dict['Name']:DerisWengdict['Age']:7Toaccessthevaluesinthedictionarydict={'Name':'DerisWeng','Age':7,'Class':'First'}print("dict['Name']:",dict['Name'])print("dict['Age']:",dict['Age'])Thevaluesinthedictionarycanbeaccessedbydict[Key],thatis,placingthecorrespondingkeyinthesquarebracket[].[Example]Accessingavalueinadictionarybydirectreferencedict['Name']:DerisWengdict['Age']:7Case案例訪問字典里的值dict={'Name':'DerisWeng','Age':7,'Class':'First'}print("dict['Christopher']:",dict['Christopher'])如果使用字典里沒有對應的鍵，則訪問數據時會報錯。【例】訪問字典中沒有的鍵Traceback(mostrecentcalllast):File"test1.py",line5,in<module>print("dict['Christopher']:",dict['Christopher'])KeyError:'Christopher'dict={'Name':'DerisWeng','Age':7,'Class':'First'}print("dict['Christopher']:",dict['Christopher'])Ifyouuseadictionarythatdoesnothaveacorrespondingkey,youwillgetanerrorwhenaccessingthedata.[Example]AccessingakeythatisnotinthedictionaryTraceback(mostrecentcalllast):File"test1.py",line5,in<module>print("dict['Christopher']:",dict['Christopher'])KeyError:'Christopher'ToaccessthevaluesinthedictionaryCase案例訪問字典里的值dict={'Name':'DerisWeng','Age':7,'Class':'First'}print(“dict[‘Christopher’]:”,dict.get(‘Christopher’))利用get方法訪問【例】利用get方法，訪問字典中沒有的鍵dict[‘Christopher’]:Nonedict={'Name':'DerisWeng','Age':7,'Class':'First'}print(“dict[‘Christopher’]:”,dict.get(‘Christopher’))Accesswithgetmethod[Example]Usethegetmethodtoaccesskeysnotinthedictionarydict[‘Christopher’]:NoneToaccessthevaluesinthedictionaryCase問題:根據key得到value的方法有哪幾種？dict[Key]dict.get（Key）提問Question:Whatarethemethodstogetthevalueaccordingtothekey?dict[Key]dict.get（Key）AskaquestionPython語言程序設計《修改字典》PythonLanguageProgrammingModifyingDictionaries案例修改字典dict={'Name':'DerisWeng','Age':7,'Class':'First'}dict['Age']=18;

dict['School']="WZVTC"

print("dict['Age']:",dict['Age'])print("dict['School']:",dict['School'])通過直接引用賦值的方式對字典進行修改【例】修改字典dict['Age']:18dict['School']:WZVTC#更新Age#添加信息CaseModifythedictionarydict={'Name':'DerisWeng','Age':7,'Class':'First'}dict['Age']=18;

dict['School']="WZVTC"

print("dict['Age']:",dict['Age'])print("dict['School']:",dict['School'])modificationstothedictionarybydirectreferenceassignment[Example]Modifythedictionarydict['Age']:18dict['School']:WZVTC#UpdateAge#Addinformation問題:對字典進行修改時，key在字典中存在與不存在會有什么區別？如果dict[Key]中的Key在字典中不存在，則賦值語句將向字典中添加新內容，即增加新的鍵值對；如果dict[Key]中的Key在字典中存在，則賦值語句將修改字典中的內容。提問Question:Whenmodifyingadictionary,whatisthedifferencebetweentheexistenceandnonexistenceofakeyinthedictionary?Ifthekeyindict[Key]doesnotexistinthedictionary,theassignmentstatementwilladdnewcontenttothedictionary,thatis,addanewkeyvaluepair;Ifthekeyindict[Key]existsinthedictionary,theassignmentstatementwillmodifythecontentinthedictionary.AskaquestionPython語言程序設計《刪除字典元素》PythonLanguageProgrammingDeletingDictionaryElements31可以用del命令刪除單一的元素或者刪除整個字典，也可以用clear清空字典。【例】刪除字典元素dict={'Name':'Runoob','Age':7,'Class':'First'}

deldict[‘Name’]#刪除鍵‘Name’dict.clear()#刪除字典deldict#刪除字典print(“dict[‘Age’]:”,dict[‘Age’])print(“dict[‘School’]:”,dict[‘School’])會發生異常，因為執行del操作后字典不再存在。案例刪除字典元素32Youcanusethedelcommandtodeleteasingleelementordeletetheentiredictionary,orclearthedictionary.[Example]Deletingdictionaryelementsdict={'Name':'Runoob','Age':7,'Class':'First'}

Deldict['Name']#Deletekey'Name'Dict.clear()#DeletedictionaryDeldict#Deletedictionaryprint(“dict[‘Age’]:”,dict[‘Age’])print(“dict[‘School’]:”,dict[‘School’])Anexceptionoccursbecausethedictionarynolongerexistsafterthedeloperation.DeletingdictionaryelementsCasePython語言程序設計《字典鍵的特性》PythonLanguageProgrammingCharacterizationofDictionaryKeys35兩個重要的點需要記住：【例】重復出現的情況dict={'Name':'DerisWeng','Age':7,'Name':'DerisWeng'}

print(“dict[‘Name’]:”,dict[‘Name’])dict[‘Name’]:DerisWeng1）不允許同一個鍵出現兩次。創建時如果同一個鍵被賦值兩次，后一個值會被記住。案例字典鍵的特性36Twoimportantpointstoremember.[Example]Repeatedoccurrencesdict={'Name':'DerisWeng','Age':7,'Name':'DerisWeng'}

print(“dict[‘Name’]:”,dict[‘Name’])dict[‘Name’]:DerisWeng1)Donotallowthesamekeytoappeartwice.Ifthesamekeyisassignedtwiceduringcreation,thelattervaluewillberemembered.CharacterizationofdictionarykeysCase37兩個重要的點需要記住：【例】不能用列表作為鍵dict={['Name‘]:'DerisWeng','Age':7}

print(“dict[‘Name’]:”,dict[‘Name’])報錯2）鍵必須不可變，所以可以用數字，字符串或元組充當，而用列表就不行。案例字典鍵的特性38[Example]Youcan'tusealistasakeydict={['Name‘]:'DerisWeng','Age':7}

print(“dict[‘Name’]:”,dict[‘Name’])Reportanerror2)Thekeymustbeimmutable,soitcanbefilledwithnumbers,stringsortuples,butnotwithlists.CharacterizationofdictionarykeysCaseTwoimportantpointstoremember.Python語言程序設計39《字典的方法》PythonLanguageProgramming40TheDictionaryApproach41【字典的方法】知識點6dict.clear()

刪除字典內所有元素dict.copy()

返回一個字典的淺復制dict.fromkeys()

創建一個新字典，以序列seq中元素做字典的鍵，val為字典所有鍵對應的初始值dict.get(key,default=None)

返回指定鍵的值，如果值不在字典中返回default值keyindict

如果鍵在字典dict里返回true，否則返回false2字典知識要點42[Dictionarymethod]Knowledgepoint6dict.clear()

Deleteallelementsinthedictionarydict.copy()

Returnsashallowcopyofadictionarydict.fromkeys()

Createanewdictionary,usetheelementsinthesequenceseqasthedictionarykeys,andvalistheinitialvaluecorrespondingtoallthekeysinthedictionarydict.get(key,default=None)

Returnthevalueofthespecifiedkey.Ifthevalueisnotinthedictionary,returnthedefaultvaluekeyindict

Ifthekeyreturnstrueinthedictionarydict,otherwiseitreturnsfalse2DictionaryKnowledgePoints43radiansdict.items()

以列表返回可遍歷的(鍵,值)元組數組radiansdict.keys()

以列表返回一個字典所有的鍵radiansdict.setdefault(key,default=None)

和get()類似,但如果鍵不存在于字典中，將會添加鍵并將值設為defaultradiansdict.update(dict2)

把字典dict2的鍵/值對更新到dict里radiansdict.values()

以列表返回字典中的所有值2字典知識要點[Dictionarymethod]Knowledgepoint644radiansdict.items()

Returnsanarrayoftraversable(key,value)tuplesasalistradiansdict.keys()

Returnsallthekeysofadictionaryasalistradiansdict.setdefault(key,default=None)

Similartoget(),butifthekeydoesnotexistinthedictionary,thekeywillbeaddedandthevaluewillbesettodefaultradiansdict.update(dict2)

Updatethekey/valuepairofdict2todictradiansdict.values()

Returnsallthevaluesinthedictionaryasalist2DictionaryKnowledgePoints[Dictionarymethod]Knowledgepoint645【字典的方法】知識點6pop(key[,default])

刪除字典給定鍵key所對應的值，返回值為被刪除的值。key值必須給出。否則，返回default值。popitem()

隨機返回并刪除字典中的一對鍵和值。2字典知識要點46pop(key[,default])

Deletethevaluecorrespondingtothekeygiveninthedictionary.Thereturnvalueisthedeletedvalue.Thekeyvaluemustbegiven.Otherwise,thedefaultvalueisreturned.popitem()

Randomlyreturnsandremovesapairofkeysandvaluesfromthedictionary.2DictionaryKnowledgePoints[Dictionarymethod]Knowledgepoint6Python語言程序設計47《字典內置函數》PythonLanguageProgramming48DictionaryBuilt-inFunctions49【字典內置函數】知識點7函數及描述實例len(dict)

計算字典元素個數，即鍵的總數。>>>dict=

{'Name':

'Runoob',

'Age':7,

'Class':

'First'}>>>len(dict)3str(dict)

輸出字典，以可打印的字符串表示。>>>dict=

{'Name':

'Runoob',

'Age':7,

'Class':

'First'}>>>str(dict)"{'Name':'Runoob','Class':'First','Age':7}"type(variable)

返回輸入的變量類型，如果變量是字典就返回字典類型。>>>dict=

{'Name':

'Runoob',

'Age':7,

'Class':

'First'}>>>type(dict)<class

'dict'>2字典知識要點50[DictionaryBuilt-inFunctions]Knowledgepoint7functionsanddescriptionsInstancelen(dict)

Countsthenumberofdictionaryelements,i.e.,thetotalnumberofkeys.>>>dict=

{'Name':

'Runoob',

'Age':7,

'Class':

'First'}>>>len(dict)3str(dict)

Outputsthedictionaryasaprintablestring.>>>dict=

{'Name':

'Runoob',

'Age':7,

'Class':

'First'}>>>str(dict)"{'Name':'Runoob','Class':'First','Age':7}"type(variable)

Returnsthetypeoftheinputvariable,orthedictionarytypeifthevariableisadictionary.>>>dict=

{'Name':

'Runoob',

'Age':7,

'Class':

'First'}>>>type(dict)<class

'dict'>2DictionaryKnowledgePointsPython語言程序設計51《集合的定義+添加集合元素》PythonLanguageProgramming52DefinitionofaCollection+AddingCollectionElements知識要點53【集合的定義】知識點1集合：確定的一堆“東西（元素）”，無序的，不重復的思考：對比列表？KnowledgePoints54[Definitionofset]Knowledgepoint1Set:adefinitepileof"things(elements)",unordered,non-repeatingThink:Compareandcontrastlists?知識要點55set1={'張三'，'李四'，'王五'}【例】定義一個簡單的集合實例集合注意事項：（1）所有元素放在花括號{}里。（2）元素間以逗號(,)分隔。（3）可以有任意數量的元素（4）不能有可變元素（例如，列表、集合、字典）【集合的定義】知識點1【例】定義一個空集合set1=set()注意：不能使用{}定義空集合，因為{}表示空字典KnowledgePoints56Set1={'ZhangSan','LiSi','WangWu'}[Example]DefineasimplecollectioninstancethatAssemblyNotes.(1)Allelementsareplacedincurlybraces{}.(2)Elementsareseparatedbyacomma(,).(3)canhaveanynumberofelements(4)Cannothavemutableelements(e.g.,lists,sets,dictionaries).[Example]Defineanemptysetthatset1=set()Caution.Youcan'tuse{}todefineanemptycollection,Since{}denotestheemptydictionary,the[Definitionofset]Knowledgepoint1知識要點57【添加集合元素】知識點2添加集合元素有兩種方式1.使用add方法2.使用update方法123name={'tom','danny'}name.add('smith')print(name){'tom','danny','smith'}【例】使用add(元素值)

添加單個元素KnowledgePoints58[Addcollectionelement]Knowledgepoint2Therearetwowaystoaddcollectionelements1Usetheaddmethod2.Usetheupdatemethod123name={'tom','danny'}name.add('smith')print(name){'tom','danny','smith'}[Example]Useadd(elementvalue)toaddasingleelement知識要點59【添加集合元素】知識點2添加集合元素有兩種方式1.使用add方法2.使用update方法123name={'tom','danny'}name.update(['king','james'])print(name){'king','james','tom','danny'}【例】使用update(任意列表或集合)

添加多個元素123name={'tom','danny'}name.update(['king','james'],{'kevin','smith'})print(name){'kevin','james','king','smith','tom','danny'}注意：update參數可以是任意多個列表或集合KnowledgePoints60Therearetwowaystoaddcollectionelements1Usetheaddmethod2.Usetheupdatemethod123name={'tom','danny'}name.update(['king','james'])print(name){'king','james','tom','danny'}[Example]Useupdate(anylistorset)toaddmultipleelements123name={'tom','danny'}name.update(['king','james'],{'kevin','smith'})print(name){'kevin','james','king','smith','tom','danny'}Caution.Theupdateparametercanbeanynumberoflistsorcollections[Addcollectionelement]Knowledgepoint2Python語言程序設計61《刪除集合元素》PythonLanguageProgramming62DeletionofSetElements知識要點63【刪除集合元素】知識點3刪除集合元素有四種方式 1.使用remove方法2.使用discard方法

3.使用pop方法4.使用clear方法123name={'king','james','tom','danny'}name.remove('james')print(name){'danny','tom','king'}【例】使用remove(指定元素)

刪除指定元素KnowledgePoints64Therearefourwaystodeleteelementsofacollection,the