Python异常课件教学

程序设计错误1语法错误运行时错误逻辑错误6=x*2x=3/0area=2*3.14*3异常（Exception）Traceback(mostrecentcalllast):

File"<pyshell#0>",line1,in<module>1/0ZeroDivisionError:divisionbyzero2>>>1/0SourceTraceback(mostrecentcalllast):

File"<pyshell#1>",line1,in<module>y=x+1NameError:name'x'isnotdefined>>>y=x+1Source用异常对象（exceptionobject）表示异常情况异常查看异常类

dir(__builtins__)3类

名描

述BaseException所有异常的基类Exception常规异常的基类AttributeError对象不存在此属性IndexError序列中无此索引IOError输入/输出操作失败KeyboardInterrupt用户中断执行(通常输入Ctr-C)KeyError映射中不存在此键NameError找不到名字（变量）SyntaxErrorPython语法错误TypeError对类型无效的操作ValueError传入无效的参数ZeroDivisionError除(或取模)运算的第二个参数为0异常处理ify!=0:

print(x/y)else:

print('divisionbyzero')4VStry-except异常处理语句

捕捉异常9.25异常Enterthefirstnumber:aTraceback(mostrecentcalllast):

File"C:\Python\programs\exception1.py",line1,in<module>num1=int(input('Enterthefirstnumber:'))ValueError:invalidliteralforint()withbase10:'a'6#Filename:prog9-1.pynum1=int(input('Enterthefirstnumber:'))num2=int(input('Enterthesecondnumber:'))print(num1

/num2)File9.2.1try-except语句7try-except语句8#Filename:prog9-2.pytry:num1=int(input('Enterthefirstnumber:'))num2=int(input('Enterthesecondnumber:'))

print(num1/num2)except

ValueError:

print('Pleaseinputadigit!')Filetry:

被检测的语句块exceptException:

异常处理语句块try-except语句9#Filename:prog9-3.pytry:num1=int(input('Enter

the

first

number:'))num2=int(input('Enter

the

second

number:'))

print(num1/num2)except

ZeroDivisionError:

print('The

second

number

cannot

be

zero!')File9.2.2多个except子句和一个except块捕捉多个异常10多个except子句11#Filename:prog9-4.pytry:num1=int(input('Enter

the

first

number:'))num2=int(input('Enter

the

second

number:'))

print(num1/num2)except

ValueError:

print('Please

inputadigit!')except

ZeroDivisionError:

print('The

second

number

cannot

be

zero!')File一个except块捕捉多个异常12#Filename:prog9-5.pytry:num1=int(input('Enter

the

first

number:'))num2=int(input('Enter

the

second

number:'))

print(num1/num2)except(ValueError,ZeroDivisionError):

print('Invalid

input!')File空except子句13#Filename:prog9-6.pytry:num1=int(input('Enter

the

first

number:'))num2=int(input('Enter

the

second

number:'))

print(num1/num2)except:

print('Something

went

wrong!')File一了百了：except:as子句14#Filename:prog9-7.pytry:num1=int(input('Enter

the

first

number:'))num2=int(input('Enter

the

second

number:'))

print(num1/num2)except

Exception

aserr:

print('Something

went

wrong!')

print(err)Fileas子句15try:

被检测的语句块except异常类名

as错误原因名:

异常处理语句块print(错误原因名)9.2.3else子句16else子句17#Filename:prog9-8.pytry:num1=int(input('Enterthefirstnumber:'))num2=int(input('Enter

the

second

number:'))

print(num1/num2)except(ValueError,ZeroDivisionError):

print('Invalid

input!')else:

print('Aha,Iamsmart.')FileEnterthefirstnumber:3Enterthesecondnumber:50.6Aha,Iamsmart.加入循环18#Filename:prog9-9.pywhileTrue:

try:num1=int(input('Enterthefirstnumber:'))

num2=int(input('Enter

the

second

number:'))

print(num1/num2)

except

ValueError:

print('Please

input

adigit!')

except

ZeroDivisionError:

print('The

second

number

cannot

be

zero!')

else:

breakFileEnterthefirstnumber:aPleaseinputadigit!Enterthefirstnumber:3Enterthesecondnumber:0Thesecondnumbercannotbezero!Enterthefirstnumber:3Enterthesecondnumber:50.6break语句的位置19#Filename:prog9-9’.pywhileTrue:

try:num1=int(input('Enterthefirstnumber:'))num2=int(input('Enter

the

second

number:'))

print(num1/num2)

break

except

ValueError:

print('Please

input

adigit!')

except

ZeroDivisionError:

print('The

second

number

cannot

be

zero!')File改写prog9-9.pybreak语句的位置20#Filename:prog9-11.pywhileTrue:try:num1=int(input('Enter

the

first

number:'))num2=int(input('Enter

the

second

number:'))

print(num1/num2)

break

exceptExceptionaserr:

print(err)Filebreak语句的位置21#Filename:prog9-12.pyaList=[1,2,3,4,5]i=0whileTrue:

try:

print(aList[i])

except

IndexError:

print('index

error')

break

else:i+=1File9.2.4finally子句22finally子句23#Filename:prog9-13.pydeffinallyTest():

try:x=int(input('Enterthefirstnumber:'))

y=int(input('Enter

the

second

number:'))

print(x/y)

return1

except

Exception

aserr:

print(err)

return0

finally:

print('It

isafinallyclause.')result=finallyTest()print(result)FileEnterthefirstnumber:3Enterthesecondnumber:50.6Itisafinallyclause.1Enterthefirstnumber:3Enterthesecondnumber:0divisionbyzeroIti