《Python语言程序设计》课件-第二章（中英文课件）

Python语言程序设计【while循环与循环的中止】PythonLanguageProgramming[Whileloopandlooptermination]知识点【while循环】while循环基本格式程序流程图代码结构while条件表达式：#表达式为真则执行语句1到语句n语句1语句2……语句n其他语句KnowledgePoints[WhileLoop]BasicformatofwhileloopprogramflowchartscodestructureWhileconditionalexpression:

#Iftheexpressionistrue,executestatements1ton

Statement1

Statement2……

Statementnotherstatements知识点【while循环】【例】计算1到100的总和1.确定循环次数，利用循环变量的方式代码结构sum=0

i=1

whilei<=100:

sum=sum+i

i+=1

print("1到100之和为:%d"%(sum))[Example]Calculatethesumof1to1001.Determinethenumberofcycles,utilizingcyclicvariablescodestructuresum=0

i=1

whilei<=100:

sum=sum+i

i+=1

Print("Thesumof1to100is:%d"%

(sum))KnowledgePoints[WhileLoop]知识点【while循环】【例】根据输入的数字，求出它的所有因子。2.循环次数不定，直至表达式为‘0’或‘Flase’代码结构j=2

i=eval(input("请输入一个整数："))

answer="它的所有因子为:"

whilei>j:

ifi%j==0:

answer+=str(j)+","

j+=1

print(answer)[Example]Basedontheinputnumber,findallthefactorsofit.2.Thenumberofcyclesisuncertainuntiltheexpressionis'0'or'Flase'codestructureKnowledgePoints[WhileLoop]j=2

i=eval(input("Pleaseenteraninteger:"))

answer="Allitsfactorsare:"

whilei>j:

ifi%j==0:

answer+=str(j)+","

j+=1

print(answer)知识点【while循环】【例】用while语句在屏幕中打印出数字0-92.循环次数不定，直至表达式为‘0’或‘Flase’代码结构i=0

whilei<10:

print(i)

i=i+1#i的值不断递增，从而确保循环能够终止。[Example]Printthenumbers0-9onthescreenwiththewhilestatementcodestructurei=0

whilei<10:

print(i)

i=i+1#iisincreasingtoensurethattheloopcanbeterminated.KnowledgePoints[WhileLoop]2.Thenumberofcyclesisuncertainuntiltheexpressionis'0'or'Flase'知识点【while循环】【例】无限循环3.通过设置条件表达式永远不为false来实现无限循环

代码结构while1==1:#表达式永远成立

num=int(input("输入一个数字:"))

print("你输入的数字是:",num)

print("再见!")[Example]Infiniteloop3.Realizeinfiniteloopbysettingtheconditionalexpressiontoneverbefalsecodestructurewhile1==1:#Theexpressionisalwaystrue

num=int(input("Enteranumber:"))

print("Thenumberyouenteredis:",,num)

print("Goodbye!")KnowledgePoints[WhileLoop]知识点【while循环】【例】while…else条件语句4.while循环使用else语句代码结构count=0

whilecount<5:

print(count,"小于5")

count=count+1

else:

print(count,"大于或等于5")[Example]While.elseconditionalstatement4.WhileloopusingelsestatementcodestructureKnowledgePoints[WhileLoop]count=0

whilecount<5:

print(count,"lessthan5")

count=count+1

else:

print(count,"greaterthanorequalto5")知识点【while循环】【例】简单语句组5.简单语句组代码结构while1==1:print('HelloDerisweng!')如果while循环体中只有一条语句，可以将该语句与while写在同一行中。[Example]Groupofsimplestatements5.Groupsofsimplestatementscodestructurewhile1==1:print('HelloDerisweng!')Ifthereisonlyonestatementinthebodyofthewhileloop,thestatementcanbewrittenonthesamelineaswhile.KnowledgePoints[WhileLoop]知识点【循环的中止】【例】求20以内的所有质数（素数）1.利用break中止循环的流程代码结构i=2

whilei<21:#表示求质数的范围是从2-21

j=2#对于每个i因子，都从2开始计算

whilej<i/2:#如果在2-i/2的范围内有把i整除的数，则i不是质数

ifi%j==0:

break

#若已经整除就没有必要测试其他因子，终止循环

j+=1

ifj>=i/2:

#如果关于j的循环都已经进行完毕，说明在2-i/2的范围内无因子，i是质数

print(i,'是质数')

i+=1Example:Findallprimenumbersupto20.1.Usebreaktoabortthecycleprocesscodestructurei=2

whilei<21:#indicatesthattherangeofprimenumberisfrom2-21

j=2#Foreachifactor,startfrom2

whilej<i/2:#Ifthereisanumberwithintherangeof2-i/2thatdividesi,iisnotaprimenumber

ifi%j==0:

break#Ifithasbeendivided,itisunnecessarytotestotherfactorsandterminatetheloop

j+=1

ifj>=i/2:

#Ifthecycleaboutjhasbeencompleted,itmeansthatthereisnofactorintherangeof2-i/2,andiisaprimenumber

Print(i,'isaprimenumber')

i+=1KnowledgePoints[Abortingthecycle]知识点【循环的中止】1.break语句可以从循环语句的循环体内跳出循环。2.continue语句仅仅是从循环语句的循环体内跳到下一个迭代中。1.Thebreakstatementcanjumpoutoftheloopfromtheloopbodyoftheloopstatement.2.Thecontinuestatementonlyjumpsfromtheloopbodyoftheloopstatementtothenextiteration.KnowledgePoints[Abortingthecycle]Python语言程序设计【常用运算】PythonLanguageProgramming[CommonOperations]Python语言支持的运算符知识点【常用运算】算术运算符、关系运算符逻辑运算符、赋值运算符位运算符、成员运算符、身份运算符OperatorssupportedbyPythonlanguageKnowledgePoints[CommonOperations]arithmeticoperators,relationaloperatorslogicaloperators,assignmentoperatorsbitwiseoperators,membershipoperators,identityoperators知识点【常用运算】1.算术运算符运算符描述+两个对象相加-得到负数或是两个数相减*两个数相乘或是返回一个被重复若干次的字符串/两个数相除%取模：返回除法的余数**幂：x**y，返回x的y次幂//取整：返回商的整数部分123a,b=26,7

c=a//b

print("c=a//b,c=",c)【例】取整//3输出结果：1.thearithmeticoperatorsoperatorsDescription+Twoobjectsaddedtogether-togetanegativenumberortosubtracttwonumbers*Multiplytwonumbersorreturnastringrepeatedseveraltimes/Dividingtwonumbers%modulo:returnstheremainderofthedivision**Power:x**y,returnxtotheypower//rounding:returnstheintegerpartofthequotient123a,b=26,7

c=a//b

print("c=a//b,c=",c)[Example]Rounding//3Outputresult：KnowledgePoints[CommonOperations]知识点【常用运算】2.关系运算符运算符描述==等于!=不等于>

大于<

小于>=大于等于<=小于等于12x,y=35,10

print(x!=y)【例】不等于！=True输出结果：2.RelationaloperatorsoperatorsDescription==Equivalent!=Notequalto>

Greaterthan<

Lessthan>=greaterthanorequalto<=lessthanorequalto12x,y=35,10

print(x!=y)[Example]Notequalto!=TrueKnowledgePoints[CommonOperations]Outputresult：知识点【常用运算】3.逻辑运算符运算符描述and布尔"与"or布尔"或"not布尔"非"1234x,y=35,10

print(xandy)

print(xory)

print(notx)【例】逻辑运算符1035False输出结果：3.LogicaloperatorsoperatorsDescriptionandBoolean"vs."orBoolean"or"notBoolean"non"1234x,y=35,10

print(xandy)

print(xory)

print(notx)[Example]Thelogicaloperator1035FalseKnowledgePoints[CommonOperations]Outputresult：知识点【常用运算】4.赋值运算符运算符描述=x=y将y赋值给x+=x+=y等效于x=x+y-=x-=y等效于x=x-y*=x*=y等效于x=x*y/=x/=y等效于x=x/y%=x%=y等效于x=x%y**=x**=y等效于x=x**y//=x//=y等效于x=x//y123x,y=10,3

x/=y

print(x)【例】赋值运算/=3.3333333333333335输出结果：4.theassignmentoperatoroperatorsDescription=X=yassignsytox+=X+=yisequivalenttox=x+y-=X-=yisequivalenttox=x-y*=X*=yisequivalenttox=x*y/=X/=yisequivalenttox=x/y%=X%=yisequivalenttox=x%y**=X**=yisequivalenttox=x**y//=X//=yisequivalenttox=x//y123x,y=10,3

x/=y

print(x)[Example]Assignmentoperation/=3.3333333333333335KnowledgePoints[CommonOperations]Outputresult：知识点【常用运算】5.位运算符运算符描述&按位与运算符：参与运算的两个值,如果两个相应位都为1,则该位的结果为1，否则为0|按位或运算符：只要对应的二个二进位有一个为1时，结果位就为1。^按位异或运算符：当两对应的二进位相异时，结果为1~按位取反运算符：对数据的每个二进制位取反，即把1变为0，把0变为1。<<

左移动运算符：运算数的各二进位全部左移若干位，由"<<"右边的数指定移动的位数，高位丢弃，低位补0。>>

右移动运算符：把">>"左边的运算数的各二进位全部右移若干位，">>"右边的数指定移动的位数1234a=9#9=00001001

b=3#3=00000011

c=0

c=a&b#1=00000001【例】按位与5.bitwiseoperatorsoperatorsDescription&Bybitwiththeoperator:thetwovaluesinvolvedintheoperation,ifthetwocorrespondingbitsare1,theresultofthebitis1,otherwise0|Bitwiseoroperator:Wheneveroneofthetwocorrespondingbinarybitsisone,theresultbitisone.^Bitwisedifferentoroperator:whenthetwocorrespondingbinarybitsaredifferent,theresultis1~Bitwiseinverseoperator:invertseachbinarybitofdata,i.e.,changes1to0and0to1.<<

Leftshiftoperator:allbinarybitsoftheoperatorareshiftedleftbyanumberofbits,thenumbertotherightof"<<"specifiesthenumberofbitstobeshifted,thehigherbitsarediscardedandthelowerbitsarezeroed.>>

Rightshiftoperator:shiftsallbinarydigitsoftheoperatortotheleftof">>"totherightbyacertainnumberofdigits,thenumbertotherightof">>"specifiesthenumberofdigitstobeshifted,andthenumbertotherightof">>"specifiesthenumberofdigitstobeshifted1234a=9#9=00001001

b=3#3=00000011

c=0

c=a&b#1=00000001[Example]BybitwithKnowledgePoints[CommonOperations]知识点【常用运算】6.成员运算符运算符描述in如果在指定的序列中找到值返回True，否则返回False。notin如果在指定的序列中没有找到值返回True，否则返回False。FalseTrue输出结果：1234a=6

clist=[1,2,3,4,5]

print(ainclist)

print(anotinclist)【例】成员运算6.MembershipoperatorsoperatorsDescriptioninIfavalueisfoundinthespecifiedsequence,itreturnsTrue;otherwise,itreturnsFalse.notinIfnovalueisfoundinthespecifiedsequence,trueisreturned;otherwise,falseisreturned.FalseTrue1234a=6

clist=[1,2,3,4,5]

print(ainclist)

print(anotinclist)[Example]ThemembershipoperationKnowledgePoints[CommonOperations]Outputresult：知识点【常用运算】7.身份运算符运算符描述isis是判断两个标识符是不是引用自一个对象isnotisnot是判断两个标识符是不是引用自不同对象FalseTrueFalseTrue输出结果：1234567a,b=6,10

print(aisb)

print(aisnotb)

print(id(a)==id(b))

#id方法的返回值就是对象的内存地址

b=6

print(id(a)==id(b))【例】身份运算7.identityoperatorsoperatorsDescriptionisIsistodeterminewhethertwoidentifiersarereferencedfromanobjectisnotIsnottojudgewhethertwoidentifiersarereferencedfromdifferentobjectsFalseTrueFalseTrue1234567a,b=6,10

print(aisb)

print(aisnotb)

print(id(a)==id(b))

#Thereturnv