python学习笔记9——第八章 异常
程序员文章站
2022-06-15 22:43:22
...
第八章 异常
1.
(1)捕捉异常,try & except
>>> try:
x = input("x: ")
y = input("y: ")
print x/y
except ZeroDivisionError:
print "The second number can't be zero!"
x: 1
y: 0
The second number can't be zero!
(2)捕捉异常并重新引发
>>> class MuffledCalculator:
muffled = False; #屏蔽开关的标志
def calc(self, expr):
try:
return eval(expr)
except ZeroDivisionError:
if self.muffled: #若屏蔽开着,则捕捉异常并进行处理
print "Division by zero is illegal"
else: #若屏蔽关着,则捕捉异常并重新引发
raise #except捕捉到了异常,raise重新引发异常
>>> calculator = MuffledCalculator()
>>> calculator.calc('10/2')
5
>>> calculator.calc('10/0') #屏蔽机制未打开,因为muffled = False
Traceback (most recent call last):
File "<pyshell#29>", line 1, in <module>
calculator.calc('10/0') #屏蔽机制未打开,因为muffled = False
File "<pyshell#26>", line 5, in calc
return eval(expr)
File "<string>", line 1, in <module>
ZeroDivisionError: integer division or modulo by zero
>>> calculator.muffled = True #打开屏蔽机制
>>> calculator.calc('10/0')
Division by zero is illegal
(3)多个except,捕捉多个不同类型的异常
>>> try:
x = input("x: ")
y = input("y: ")
print x/y
except ZeroDivisionError:
print "Y can't be zero!"
except TypeError:
print "That wasn't a numbber, was it?"
x: 1
y: 'test'
That wasn't a numbber, was it?
(4)一个except捕捉多个类型异常,效果同(3)
>>> try:
x = input("x: ")
y = input("y: ")
print x/y
except(ZeroDivisionError, TypeError, NameError): #NameError找不到名字(变量)时引发
print 'Your numbers were bogus(wrong)...'
(5)捕捉异常对象,想让程序继续运行,又想记录错误时应用
>>> try:
x = input("x: ")
y = input("y: ")
print x/y
except(ZeroDivisionError, TypeError), e: #多个异常时也只需提供一个参数e,是一个元组
print "Invalid input:", e
x: 1
y: 0
Invalid input: integer division or modulo by zero
x: 1
y: 'test'
Invalid input: unsupported operand type(s) for /: 'int' and 'str'
(6)捕捉所有异常,except后不加东西
>>> try:
x = input("x: ")
y = input("y: ")
print x/y
except:
print "Something wrong happend..."
x:
Something wrong happend...
>>>
(7) try & except & else
>>> while True:
try:
x = input("x: ")
y = input("y: ")
print 'x/y is', x/y
except:
print "Invalid input. Please try again."
else: #只有在异常没发生,也就是输入正确的时候,循环才退出
break
x: 1
y: 0
x/y is Invalid input. Please try again.
x: 2
y: 'test'
x/y is Invalid input. Please try again.
x:
Invalid input. Please try again.
x: 1
y: 2
(8) try & finally, try & except & finally, try & except & else & finally
--不管是否发生异常,finally语句块一定会执行
>>> try:
1/0
except NameError:
print "Unknown variable"
else:
print "That went well!"
finally:
print "Cleaning up."
实例
>>> def describePerson(person):
print "Description of", person['name']
print 'Age:', person['age']
try:
print 'Occupation: ' + person['occupation'] #不能用逗号连接,若用逗号,则在异常发生前就打印了pccupation
except KeyError: #键不存在
pass
>>> person = {'name': 'Sun', 'age': 32}
>>> describePerson(person) #捕获异常并处理
Description of Sun
Age: 32
#如果最后一句为print 'Occupation:', person['occupation']
#则出现
>>> describePerson(person)
Description of Sun
Age: 32
Occupation:
#所以要用加号连接,不用逗号,防止在异常发生前就被打印。
上一篇: Python第八章-异常