《Python语言程序设计》课件-第四章 （中英文课件）

Python语言程序设计【函数的定义和调用】PythonLanguageProgramming[Definitionandinvocationoffunctions]def

function_name(arg1,arg2[,...]): statement [returnvalue]知识点【函数的定义和调用】函数定义示例函数的调用def函数名(参数列表):

函数体defsumOf(a,b):

returna+ba=1

b

=2

c=sumOf(a,b)

print(str(c))1.函数通过def定义注意：该行结尾一定要加上冒号!!def

function_name(arg1,arg2[,...]): statement [returnvalue]KnowledgePoints[Definitionandinvocationoffunctions]functiondefinitionExamplefunctioniscalledDeffunctionname(parameterlist):

functionbodydefsumOf(a,b):

returna+ba=1

b

=2

c=sumOf(a,b)

print(str(c))1.FunctionsaredefinedbydefNote:Makesuretoputacolonattheendofthatline!!!!def

function_name(arg1,arg2[,...]): statement [returnvalue]知识点【函数的定义和调用】2.函数名的要求（1）函数名必须以下划线或字母开头，可以包含任意字母、数字或下划线的组合。不能使用任何的标点符号，空格也不可以；（2）函数名是区分大小写的；（3）函数名不能用保留字。3.函数形参和实参函数中的参数名称为‘形参’，调用函数时传递的值为‘实参’。def

function_name(arg1,arg2[,...]): statement [returnvalue]2.Requirementsforfunctionnames(1)functionnamemuststartwithanunderscoreorletter,cancontainanycombinationofletters,numbersorunderscores.Cannotuseanypunctuation,spacesarenotallowed;(2)Functionnamesarecase-sensitive;(3)Functionnamescannotusereservedwords.3.functionformandrealparametersThenameoftheparameterinthefunctionis'formalparameter',Thevaluepassedwhenthefunctioniscalledisa'realparameter'.KnowledgePoints[Definitionandinvocationoffunctions]知识点【函数的定义和调用】3.函数形参和实参函数定义时的参数名称为‘形参’，调用函数时传递的值为‘实参’。观察2：调用函数fun（）前后k的值的变化观察1：形参和实参形参：a实参：k没有任何变化！！！3.functionformandrealparametersThenameoftheparameterwhendefiningthefunctionis'formalparameter',andthevaluepassedwhencallingthefunctionis'realparameter'.Observe2:Changeofkvaluebeforeandaftercallingfunctionfun()Observation1:FormalandrealparametersFormalparameter:aActualparameter:kNothinghaschanged!!!!KnowledgePoints[Definitionandinvocationoffunctions]提问【函数的定义和调用】问题1:

关于函数名，下列说法正确的是（）A.函数名必须以下划线和数字开头B.函数名可以包含任意字母、数字或下划线的组合C.函数名能使用任何的标点符号D.函数名不区分大小写问题2:

说出函数形参和实参的区别。Askaquestion[Definitionandinvocationoffunctions]Question1:Regardingfunctionnames,thefollowingstatementsarecorrect()A.FunctionnamesmuststartwithanunderscoreandanumberB.Thefunctionnamecancontainanycombinationofletters,numbers,orunderscoresC.FunctionnamescanuseanypunctuationD.FunctionnamesarenotcasesensitiveQuestion2:Namethedifferencebetweenformalandrealparametersofafunction.Python语言程序设计【函数参数】PythonLanguageProgramming[FunctionParameters]知识点【函数参数】函数的参数分类：1.必需参数2．默认参数3．关键字参数4.不定长参数5.匿名函数中的参数KnowledgePoints[FunctionArguments]Classificationofargumentstofunctions：1.Requiredparameters2.Defaultparameters3.Keywordparameters4.Indefinitelengthparameters5.Parametersinanonymousfunctions知识点【函数参数】1.必需参数指的是函数要求传入的参数，调用时必须以正确的顺序传入，并且调用时的数量必须和声明时一致，否则会出现语法错误。【例】带必需参数的函数sayHello1234567defsayHello(name):

print("Hello!"+name)

return

#调用sayHello函数

sayHello("DerisWeng")

sayHello()调用sayHello(“DerisWeng”)Hello!DerisWeng调用sayHello()报错!!![FunctionArguments]1.Requiredparametersreferstothefunctionrequiredtopassparameters,thecallmustbepassedinthecorrectorder,andthenumberofcallsmustbeconsistentwiththedeclaration,otherwisetherewillbesyntaxerrors.[Example]SayHellofunctionwithrequiredparameters1234567defsayHello(name):

print("Hello!"+name)

return

#CallthesayHellofunction

sayHello("DerisWeng")

sayHello()CallsayHello("DerisWeng")Hello!DerisWengCallsayHello()ErrorReporting!!!!KnowledgePoints知识点【函数参数】2.默认参数指的是当函数中的参数设置了默认值，在调用函数时，如果没有给该参数传递任何值，则函数将会使用默认值。【例】带默认参数的函数sayHello1234567defsayHello(name,times=1):

print(("Hello!"+name)*times)

return

#调用sayHello函数

sayHello("DerisWeng")

sayHello("DerisWeng",3)调用sayHello(“DerisWeng”)Hello!DerisWeng调用sayHello(“DerisWeng”,3)Hello!DerisWengHello!DerisWengHello!DerisWeng[FunctionArguments]2.thedefaultparametersmeansthatwhenadefaultvalueissetforaparameterinafunction,thefunctionwillusethedefaultvalueifnovalueispassedtotheparameterwhenthefunctioniscalled.[Example]ThefunctionsayHellowithdefaultparameters1234567defsayHello(name,times=1):

print(("Hello!"+name)*times)

return

#CallthesayHellofunction

sayHello("DerisWeng")

sayHello("DerisWeng",3)CallsayHello("DerisWeng")Hello!DerisWengCallsayHello("DerisWeng",3)Hello!DerisWengHello!DerisWengHello!DerisWengKnowledgePoints知识点【函数参数】2.默认参数在声明函数形参时，先声明没有默认值的形参，然后再声明有默认值的形参。即默认值必须在非默认参数之后。上面这么定义是不允许的。123defsayHello(times=1,name):

print(("Hello!"+name)*times)

return是否正确？[FunctionArguments]Whendeclaringafunction'sformalparameter,firstdeclaretheformalparameterwithoutadefaultvalue,andthendeclaretheformalparameterwithadefaultvalue.Thatis,thedefaultvaluemustcomeafterthenon-defaultparameter.Theabovedefinitionisnotallowed.123defsayHello(times=1,name):

print(("Hello!"+name)*times)

returnIsthatcorrect?KnowledgePoints2.thedefaultparameters知识点【函数参数】3.关键字参数指的是如果某个函数有很多参数，在调用的时候通过参数名来对参数进行赋值。【例】使用关键字参数调用函数1234567defsayHello(name,times=1):

print(("Hello!"+name)*times)

return

#调用sayHello函数

sayHello(name="DerisWeng")

sayHello(times=3,name="DerisWeng")调用sayHello(name=“DerisWeng”)Hello!DerisWeng调用sayHello(times=3,name=“DerisWeng”)Hello!DerisWengHello!DerisWengHello!DerisWengKnowledgePoints[FunctionArguments]3.KeywordparametersThisreferstothefactthatifafunctionhasalotofparameters,theparameternamesareusedtoassignvaluestotheparameterswhenthefunctioniscalled.[Example]Callingafunctionwithakeywordargument1234567defsayHello(name,times=1):

print(("Hello!"+name)*times)

return

#CallthesayHellofunction

sayHello(name="DerisWeng")

sayHello(times=3,name="DerisWeng")CallsayHello(name="DerisWeng")Hello!DerisWengCallsayHello(times=3,name="DerisWeng")Hello!DerisWengHello!DerisWengHello!DerisWeng知识点【函数参数】4.不定长参数指的是函数的参数可以根据需要变化个数。【例】带有不定长参数的函数sayHello123456789defsayHello(name,*vars):

print("你好:")

print(name)

forvarinvars:

print(var)

return

#调用sayHello函数

sayHello("DerisWeng")

sayHello("DerisWeng","好好学习","天天向上")调用sayHello(“DerisWeng”)你好:DerisWeng调用sayHello(“DerisWeng”,“好好学习”,“天天向上”)你好:DerisWeng好好学习天天向上KnowledgePoints[FunctionArguments]4.IndefinitelengthparametersThisreferstothefactthatthenumberofargumentstoafunctioncanbevariedasneeded.[Example]SayHellofunctionwithvariablelengthparameter123456789defsayHello(name,*vars):

Print("Hello:")

print(name)

forvarinvars:

print(var)

return

#CallthesayHellofunction

sayHello("DerisWeng")

SayHello("DerisWeng","Studyhard","Makeprogresseveryday")CallsayHello("DerisWeng")HelloDerisWengCallsayHello("DerisWeng","goodgoodstudy","daydayup")Hello.DerisWenggoodgoodstudyDaybyday知识点【函数参数】5.匿名函数中的参数匿名函数指的是不用def关键字对函数进行定义，直接使用lambda来创建函数。。【例】利用lambda创建sum函数1234sum=lambdaa,b:a+b

#调用sum函数

print(sum(5,10))调用print(sum(5,10))15KnowledgePoints[FunctionArguments]5.parametersinanonymousfunctionsAnonymousfunctionreferstotheuseoflambdatocreateafunctionwithoutdefiningthefunctionwiththedefkeyword[Example]Uselambdatocreatesumfunction1234sum=lambdaa,b:a+b

#Callthesumfunction

print(sum(5,10))Callprint(sum(5,10))15知识点【函数参数】5.匿名函数中的参数匿名函数指的是不用def关键字对函数进行定义，直接使用lambda来创建函数。【例】利用lambda创建sayHello函数1234sayHello=lambdaname,times:print((“Hello!"+name)*times)

#调用sum函数sayHello("Derisweng",2)Hello!DeriswengHello!Derisweng[FunctionArguments]5.parametersinanonymousfunctionsAnonymousfunctionsrefertotheuseoflambdatocreatefunctionswithoutusingthedefkeywordtodefinethem.[Example]CreatesayHellofunctionwithlambda1234sayHello=lambdaname,times:print((“Hello!"+name)*times)

#CallthesumfunctionsayHello("Derisweng",2)Hello!DeriswengHello!DeriswengKnowledgePoints提问【函数参数】问题:

以下程序输出结果为？

deffun(x,y):

x=x+y

y=x-y

x=x-y

print(x,y)

x=2

y=3

fun(x,y)

print(x,y)Askaquestion[FunctionArguments]Question:Theoutputofthefollowingprogramis?deffun(x,y):

x=x+y

y=x-y

x=x-y

print(x,y)

x=2

y=3

fun(x,y)

print(x,y)Python语言程序设计【return语句】PythonLanguageProgramming[returnstatement]知识点【return语句】return语句用来返回函数的结果或者退出函数。【例】return不为None的情况123456defsum(a,b):

returna+b

#调用sum函数

total=sum(5,10)

print(total)不带参数值的return语句返回None，带参数值的return语句返回的就是参数的值。15输出结果：KnowledgePoints[returnstatement]returnstatementUsedtoreturntheresultofafunctionortoexitafunction.[Example]IfreturnisnotNone123456defsum(a,b):

returna+b

#Callthesumfunction

total=sum(5,10)

print(total)ThereturnstatementwithoutparametervaluereturnsNone,andthereturnstatementwithparametervaluereturnstheparametervalue.15Outputresult：知识点【return语句】return语句用来返回函数的结果或者退出函数。【例】return为None的情况123defsayHello(name):

print("Hello!"+name)

return#此处return可以不用写函数并非一定要包含return语句。如果函数没有包含return语句，Python将认为该函数返回的是None，即returnNone。None表示没有任何东西的特殊类型。KnowledgePoints[returnstatement][Example]WhenreturnisNone123defsayHello(name):

print("Hello!"+name)

Return#NoneedtowritereturnhereThefunctiondoesnothavetocontainareturnstatement.Ifthefunctiondoesnotcontainareturnstatement,PythonwillassumethatthefunctionreturnsNone,thatis,returnNone.Noneindicatesaspecialtypewithoutanything.returnstatementUsedtoreturntheresultofafunctionortoexitafunction.提问【return语句】问题:

如何让函数向调用者返回一个值？AskaquestionQuestion:HowcanImakeafunctionreturnavaluetothecaller?[returnstatement]Python语言程序设计【全局变量与局部变量】PythonLanguageProgramming[GlobalandLocalVariables]知识点【全局变量与局部变量】局部变量指在函数定义内声明的变量。【例】函数内为局部变量1234567defsum(a,b):

total=a+b#total在这里是局部变量.

print("函数内是局部变量:",total)

returntotal

#调用sum函数

sum(5,10)它们与函数外（即便是具有相同的名称）的其他变量没有任何关系。即变量的作用域只在函数的内部。函数内是局部变量:15输出结果：KnowledgePoints[GlobalandLocalVariables]localvariablesReferstoavariabledeclaredwithinafunctiondefinition.[Example]Alocalvariableinsideafunction1234567defsum(a,b):

Total=a+b#totalisalocalvariablehere

Print("Localvariableinfunction:",total)

returntotal

#Callthesumfunction

sum(5,10)Theyhavenothingtodowithothervariablesoutsidethefunction(eveniftheyhavethesamename).Thatis,thevariablesarescopedonlyinsidethefunction.Functionsarelocalizedwithinfunctions:15Outputresult:知识点【全局变量与局部变量】全局变量在函数外部声明的变量称为全局变量，程序中的任何地方都可以读取它。【例】利用global实现函数内访问全局变量12345678defshowName():

globalname

print("你的姓名："+name)

name="Weng"

#调用showName函数

name="Deris"

showName()

print(("你现在的姓名："+name))如果需要在函数内部访问全局变量，一般要用到global关键字。你的姓名：Deris你现在的姓名：Weng输出结果：globalvariablesAvariabledeclaredoutsideafunctioniscalledaglobalvariableandcanbereadanywhereintheprogram.[Example]Usingglobaltoaccessglobalvariableswithinafunction12345678defshowName():

globalname

Print("Yourname:"+name)

name="Weng"

#CalltheshowNamefunction

name="Deris"

showName()

Print(("Yourcurrentname:"+name))Ifyouneedtoaccessglobalvariableswithinafunction,yougenerallyneedtousetheglobalkeyword.Yourname:DerisYourcurrentname:WengKnowledgePoints[GlobalandLocalVariables]Outputresult:知识点【全局变量与局部变量】全局变量【例】没有用global的情况下，无法在函数内部修改全局变量。123456789name="Deris"

defsayHello():

print("hello"+name+"!")

defchangeName(newName):

name=newName

#调用函数

sayHello()

changeName("Weng")

sayHello()helloDeris!helloDeris!输出结果：globalvariables[Example]Whenglobalisnotused,globalvariablescannotbemodifiedinsidethefunction.123456789name="Deris"

defsayHello():

print("hello"+name+"!")

defchangeName(newName):

name=newName

#Callingfunctions

sayHello()

changeName("Weng")

sayHello()helloDeris!helloDeris!KnowledgePoints[GlobalandLocalVariables]Outputresult:知识点【全局变量与局部变量】全局变量【例】用global在函数内部修改全局变量。12345678910name="Deris"

defsayHello():

print("hello"+name+"!")

defchangeName(newName):

globalname

name=newName

#调用函数

sayHello()

changeName("Weng")

sayHello()helloDeris!helloWeng!输出结果：globalvariables[Example]Useglobaltomodifyglobalvariableswithinafunction.12345678910name="Deris"

defsayHello():

print("hello"+name+"!")

defchangeName(newName):

globalname

name=newName

#Callingfunctions

sayHello()

changeName("Weng")

sayHello()helloDeris!helloWeng!KnowledgePoints[GlobalandLocalVariables]Outputresult:提问【全局变量与局部变量】问题:全局变量与局部变量有什么区别？Askaquestion[GlobalandLocalVariables]Question:Whatisthedifferencebetweenaglobalvariableandalocalvariable?Python语言程序设计【函数作用域+模块+缩进格式】PythonLanguageProgramming[DocumentString+FormattedOutput+Built-inFunctions]知识点【函数作用域】变量的作用域指的是变量在程序中的哪些地方可以访问或者可见。1.每个模块都有自已的全局作用域。2.函数定义的对象属局部作用域，只在函数内有效，不会影响全局作用域中的对象。3.赋值对象属局部作用域，除非使用global关键字进行声明。12345678910name="Deris"

defsayHello():

print("hello"+name+"!")

defchangeName(newName):

globalname

name=newName

#调用函数

sayHello()

changeName("Weng")

sayHello()KnowledgePoints[FunctionScope]thescopeofthevariablereferstowhereintheprogramthevariableisaccessibleorvisible.1.eachmodulehasitsownglobalscope.2.functiondefinitionoftheobjectisalocalscope,onlyinthefunctionisvalid,willnotaffecttheglobalscopeoftheobject.3.Theassignmentobjectislocallyscopedunlessdeclaredwiththeglobalkeyword.12345678910name="Deris"

defsayHello():

print("hello"+name+"!")

defchangeName(newName):

globalname

name=newName

#Callingfunctions

sayHello()

changeName("Weng")

sayHello()课后练习【函数作用域】问题:课后请查阅一下什么是LEGB规则？After-schoolexercises[FunctionScope]Question:WhatareLEGBrulesafterclass?知识点【模块】模块一个包含所有定义的函数和变量的文件，模块必须以.py为后缀名。pythonhello.py这是“hello.py”模块hello12345678#hello.py

defsayHello():

str="hello"

print(str)

if__name__=="__main__":

print("这是hello.py模块")

sayHello()模块可以从其他程序中引入(import)，引入后就可以用模块中的函数和功能，从而达到代码复用的作用。>>>importhello>>>hello.__name__'hello'KnowledgePoints[Module]ModuleAfilecontainingalldefinedfunctionsandvariables.Themodulemusthavethesuffix.py.pythonhello.pyThisisthe"hello.py"modulehello12345678#hello.py

defsayHello():

str="hello"

print(str)

if__name__=="__main__":

Print("Thisisthehello.pymodule")

sayHello()Modulescanbeimportedfromotherprograms,andthenthefunctionsandfunctionsinthemodulecanbeusedtoachievecodereuse.>>>importhello>>>hello.__name__'hello'课后练习【模块】问题:模块的__name__的作用和用法？After-schoolexercises[Module]Question:Whatisthefunctionandusageofthe__name__ofthemodule?知识点【编程缩进格式】缩进指在代码行开始部分的空格。123456defsum(a,b):

returna+b

#调用sum函数

total=sum(5,10)

print(total)代码行开头的前导空白用于确定语句的分组，同样的缩进级别的语句属于同一语句块。（四个空格）或Tab（不建议使用）KnowledgePoints[ProgrammingIndentFormat]Indentreferstoaspaceatthebeginningofalineofcode.123456defsum(a,b):

returna+b

#Callthesumfunction

total=sum(5,10)

print(total)Leadingwhitespaceatthebeginningofalineofcodeisusedtodeterminethegroupingofstatementswiththesamelevelofindentationintothesamestatementblock.(fourspaces)orTab(notrecommended)知识点【编程缩进格式】缩进的错误用法！运行这段程序的结果如下：File"例1-3.py",line2print('IamPython');^ndentationError:unexpectedindent12print('Hello,')

print('IamPython')#注意此处特地在前面留了一个空格KnowledgePoints[ProgrammingIndentFormat]Wronguseofindentation!Theresultofrunningthisprogramisasfollows.File"Example1-3.py",line2print('IamPython');^ndentationError:unexpectedindent12print('Hello,')

Print('IamPython')#Notethataspaceisspeciallyleftinfront课后练习【编程缩进格式】问题:平级的语句行（代码块）的缩进可以不同吗？After-schoolexercises[ProgrammingIndentFormat]Question:Cantheindentationofleveledstatementlines(codeblocks)bedifferent?Python语言程序设计【文档字符串+格式化输出+内置函数】PythonLanguageProgramming[DocumentString+FormattedOutput+Built-inFunctions]知识点【文档字符串】文档字符串Python用三个引号标识文档字符串的开始和结尾。123456importmath

defarea(radius):

"""

returntheareaofcircle

"""

returnmath.pi*