《Python语言程序设计》课件-第六章（中英文课件）

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Python语言程序设计《字典的定义》PythonLanguageProgrammingDictionaryDefinitions同现实中的字典相似，Python的字典利用”Key－Value”机制对存入字典的数据进行快速查找定位。案例字典的定义Similartothedictionaryinreality,Python'sdictionaryusesthe"KeyValue"mechanismtoquicklysearchandlocatethedatastoredinthedictionary.Casedictionarydefinitions案例字典的定义dict1={'张三':25,'李四':16,'王五':40}d={key1:value1,key2:value2}【例】一个简单的字典实例字典注意事项：（1）键必须是唯一的，但值可以不唯一。（2）值可以取任何数据类型，但键必须是不可变的，如字符串、数字或元组。（3）字典的键值是“只读”的，所以不能对键和值分别进行初始化。键用列表类型可以吗？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案例字典的定义dic={}dic.keys=(1,2,3,4,5,6)dic.values=("a","b","c","d","e","f")【例】值是只读的，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问题1:键必须是唯一还是不唯一的？唯一的问题2:字典中的Value值可以重复吗？提问可以Question1:Dokeyshavetobeuniqueornon-unique?TheoneandonlyQuestion2:Canthevalueinthedictionaryberepeated?AskaquestionYes,youcan问题3:字典中的键用列表类型可以吗？提问值可以取任何数据类型，但键必须是不可变的，如字符串、数字或元组Question3:Isitoktousealisttypeforkeysinadictionary?Thevaluecantakeanydatatype,butthekeymustbeimmutable,suchasastring,number,ortupleAskaquestionPython语言程序设计《访问字典里的值》PythonLanguageProgrammingAccesstoDictionaryValues案例访问字典里的值dict={'Name':'DerisWeng','Age':7,'Class':'First'}print("dict['Name']:",dict['Name'])print("dict['Age']:",dict['Age'])访问字典中的值可以通过dict[Key]的方式，即把相应的键放到方括弧[]中进行访问。【例】通过直接引用访问字典中的值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案例访问字典里的值dict={'Name':'DerisWeng','Age':7,'Class':'First'}print("dict['Christopher']:",dict['Christopher'])如果使用字典里没有对应的键，则访问数据时会报错。【例】访问字典中没有的键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案例访问字典里的值dict={'Name':'DerisWeng','Age':7,'Class':'First'}print(“dict[‘Christopher’]:”,dict.get(‘Christopher’))利用get方法访问【例】利用get方法，访问字典中没有的键dict[‘Christopher’]:Nonedict={'Name':'DerisWeng','Age':7,'Class':'First'}print(“dict[‘Christopher’]:”,dict.get(‘Christopher’))Accesswithgetmethod[Example]Usethegetmethodtoaccesskeysnotinthedictionarydict[‘Christopher’]:NoneToaccessthevaluesinthedictionaryCase问题:根据key得到value的方法有哪几种？dict[Key]dict.get（Key）提问Question:Whatarethemethodstogetthevalueaccordingtothekey?dict[Key]dict.get（Key）AskaquestionPython语言程序设计《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'])通过直接引用赋值的方式对字典进行修改【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问题:对字典进行修改时，key在字典中存在与不存在会有什么区别？如果dict[Key]中的Key在字典中不存在，则赋值语句将向字典中添加新内容，即增加新的键值对；如果dict[Key]中的Key在字典中存在，则赋值语句将修改字典中的内容。提问Question:Whenmodifyingadictionary,whatisthedifferencebetweentheexistenceandnonexistenceofakeyinthedictionary?Ifthekeyindict[Key]doesnotexistinthedictionary,theassignmentstatementwilladdnewcontenttothedictionary,thatis,addanewkeyvaluepair;Ifthekeyindict[Key]existsinthedictionary,theassignmentstatementwillmodifythecontentinthedictionary.AskaquestionPython语言程序设计《删除字典元素》PythonLanguageProgrammingDeletingDictionaryElements31可以用del命令删除单一的元素或者删除整个字典，也可以用clear清空字典。【例】删除字典元素dict={'Name':'Runoob','Age':7,'Class':'First'}

deldict[‘Name’]#删除键‘Name’dict.clear()#删除字典deldict#删除字典print(“dict[‘Age’]:”,dict[‘Age’])print(“dict[‘School’]:”,dict[‘School’])会发生异常，因为执行del操作后字典不再存在。案例删除字典元素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语言程序设计《字典键的特性》PythonLanguageProgrammingCharacterizationofDictionaryKeys35两个重要的点需要记住：【例】重复出现的情况dict={'Name':'DerisWeng','Age':7,'Name':'DerisWeng'}

print(“dict[‘Name’]:”,dict[‘Name’])dict[‘Name’]:DerisWeng1）不允许同一个键出现两次。创建时如果同一个键被赋值两次，后一个值会被记住。案例字典键的特性36Twoimportantpointstoremember.[Example]Repeatedoccurrencesdict={'Name':'DerisWeng','Age':7,'Name':'DerisWeng'}

print(“dict[‘Name’]:”,dict[‘Name’])dict[‘Name’]:DerisWeng1)Donotallowthesamekeytoappeartwice.Ifthesamekeyisassignedtwiceduringcreation,thelattervaluewillberemembered.CharacterizationofdictionarykeysCase37两个重要的点需要记住：【例】不能用列表作为键dict={['Name‘]:'DerisWeng','Age':7}

print(“dict[‘Name’]:”,dict[‘Name’])报错2）键必须不可变，所以可以用数字，字符串或元组充当，而用列表就不行。案例字典键的特性38[Example]Youcan'tusealistasakeydict={['Name‘]:'DerisWeng','Age':7}

print(“dict[‘Name’]:”,dict[‘Name’])Reportanerror2)Thekeymustbeimmutable,soitcanbefilledwithnumbers,stringsortuples,butnotwithlists.CharacterizationofdictionarykeysCaseTwoimportantpointstoremember.Python语言程序设计39《字典的方法》PythonLanguageProgramming40TheDictionaryApproach41【字典的方法】知识点6dict.clear()

删除字典内所有元素dict.copy()

返回一个字典的浅复制dict.fromkeys()

创建一个新字典，以序列seq中元素做字典的键，val为字典所有键对应的初始值dict.get(key,default=None)

返回指定键的值，如果值不在字典中返回default值keyindict

如果键在字典dict里返回true，否则返回false2字典知识要点42[Dictionarymethod]Knowledgepoint6dict.clear()

Deleteallelementsinthedictionarydict.copy()

Returnsashallowcopyofadictionarydict.fromkeys()

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

Returnthevalueofthespecifiedkey.Ifthevalueisnotinthedictionary,returnthedefaultvaluekeyindict

Ifthekeyreturnstrueinthedictionarydict,otherwiseitreturnsfalse2DictionaryKnowledgePoints43radiansdict.items()

以列表返回可遍历的(键,值)元组数组radiansdict.keys()

以列表返回一个字典所有的键radiansdict.setdefault(key,default=None)

和get()类似,但如果键不存在于字典中，将会添加键并将值设为defaultradiansdict.update(dict2)

把字典dict2的键/值对更新到dict里radiansdict.values()

以列表返回字典中的所有值2字典知识要点[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】知识点6pop(key[,default])

删除字典给定键key所对应的值，返回值为被删除的值。key值必须给出。否则，返回default值。popitem()

随机返回并删除字典中的一对键和值。2字典知识要点46pop(key[,default])

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

Randomlyreturnsandremovesapairofkeysandvaluesfromthedictionary.2DictionaryKnowledgePoints[Dictionarymethod]Knowledgepoint6Python语言程序设计47《字典内置函数》PythonLanguageProgramming48DictionaryBuilt-inFunctions49【字典内置函数】知识点7函数及描述实例len(dict)

计算字典元素个数，即键的总数。>>>dict=

{'Name':

'Runoob',

'Age':7,

'Class':

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

输出字典，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)

返回输入的变量类型，如果变量是字典就返回字典类型。>>>dict=

{'Name':

'Runoob',

'Age':7,

'Class':

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

'dict'>2字典知识要点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语言程序设计51《集合的定义+添加集合元素》PythonLanguageProgramming52DefinitionofaCollection+AddingCollectionElements知识要点53【集合的定义】知识点1集合：确定的一堆“东西（元素）”，无序的，不重复的思考：对比列表？KnowledgePoints54[Definitionofset]Knowledgepoint1Set:adefinitepileof"things(elements)",unordered,non-repeatingThink:Compareandcontrastlists?知识要点55set1={'张三'，'李四'，'王五'}【例】定义一个简单的集合实例集合注意事项：（1）所有元素放在花括号{}里。（2）元素间以逗号(,)分隔。（3）可以有任意数量的元素（4）不能有可变元素（例如，列表、集合、字典）【集合的定义】知识点1【例】定义一个空集合set1=set()注意：不能使用{}定义空集合，因为{}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知识要点57【添加集合元素】知识点2添加集合元素有两种方式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)

添加单个元素KnowledgePoints58[Addcollectionelement]Knowledgepoint2Therearetwowaystoaddcollectionelements1Usetheaddmethod2.Usetheupdatemethod123name={'tom','danny'}name.add('smith')print(name){'tom','danny','smith'}[Example]Useadd(elementvalue)toaddasingleelement知识要点59【添加集合元素】知识点2添加集合元素有两种方式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)

添加多个元素123name={'tom','danny'}name.update(['king','james'],{'kevin','smith'})print(name){'kevin','james','king','smith','tom','danny'}注意：update参数可以是任意多个列表或集合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语言程序设计61《删除集合元素》PythonLanguageProgramming62DeletionofSetElements知识要点63【删除集合元素】知识点3删除集合元素有四种方式 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)

删除指定元素KnowledgePoints64Therearefourwaystodeleteelementsofacollection,the