异常处理

1 什么是异常？

异常是错误发生的信号，一旦程序出错，就会产生一个异常，应用程序未处理该异常，异常便会抛出，程序随之终止

2、常见异常类型

I:语法错误应该在程序运行前修正

if 1 >2
    print('xxxxx')

II:逻辑错误

x

l=[]
l[10000] #IndexError

class Foo:
    pass
Foo.x #AttributeError:

k={'x':1}
k['y'] #KeyError

1/0 #ZeroDivisionError

for i in 3: #TypeError:
    pass


age=input('>>: ') #ValueError
age=int(age)

3、如何处理异常

print('====>start<=====')

try:
    l=[]
    print(l[1111])
    print('====>1')
    print('====>2')
    print('====>3')
except IndexError:
    pass

print('====>end<=======')



print('====>start<=====')
try:
    l=[]
    print(l[1111])
    print('====>1')
    print('====>2')
    print('====>3')
except IndexError as e:
    print('===>',e)

print('====>end<=======')




print('====>start<=====')
try:
    l=[]
    # print(l[1111])
    print('====>1')
    d={}
    d['k']
    print('====>2')
    print('====>3')
except IndexError as e:
    print('===>',e)
except KeyError as e:
    print('----',e)

print('====>end<=======')



print('====>start<=====')
try:
    l=[]
    # print(l[1111])
    print('====>1')
    d={}
    d['k']
    print('====>2')
    print('====>3')
except IndexError:
    pass
except KeyError:
    pass
except Exception as e:
    print('万能异常--->',e)

print('====>end<=======')



print('====>start<=====')
try:
    l=[]
    print(l[1111])
    # print('====>1')
    d={}
    # d['k']
    # print('====>2')
    # print('====>3')
except IndexError:
    pass
except KeyError:
    pass
except Exception as e:
    print('万能异常--->',e)
else:
    print('没有异常发生的时候触发')
finally:
    print('有没有异常都触发')


print('====>end<=======')



'''
try:
    conn=connect('1.1.1.1',3306)
    conn.execute('select * from db1.t1')
finally:
    conn.close()
'''

# stus=['egon','alex','wxxx']
ip_list=[
    # '1.1.1.1:8080',
    # '1.1.1.2:8081',
    # '1.1.1.3:8082',
]

if len(ip_list) == 0:
    raise TypeError
assert len(ip_list) > 0

print('从ip_list取出ip地址，验证可用性')



class MyException(BaseException):
    def __init__(self,msg):
        super(MyException,self).__init__()
        self.msg=msg

    def __str__(self):
        return '<%s>' %self.msg

raise MyException('类型错误') #异常的值：print(obj)




age=input('>>: ')
if age.isdigit():
    age=int(age)

    if age > 50:
        print('====>too big')