python异常

一、异常类型
1、属性错误AttributeError

2、索引错误IndexError
3、数值错误’ValueError

4、类型错误TypeError

5、名称错误NameError

6、除零错误ZeroDivisionError
二、捕获异常

程序执行时遇到异常会中断，当需要在遇到异常时做出一些处理而不是中断程序
1、try…except…
(1)

try:
    lsm=int(input('lsm='))
    print(6/lsm)
except:
    print("can't divide 0")
>>>lsm=0
>>>can't divide 0

(2)设置捕获特定的异常
try:
    lsm=int(input('lsm='))
    print(6/lsm)
except(ZeroDivisionError):#指定捕获的异常类型
    print("can't divide 0")
>>>lsm=0
>>>can't divide 0

2、try…except…else
else后面的代码是没发生异常时执行
(1)

try:
    lsm=6/2
except(ZeroDivisionError,NameError) as e:#指定捕获的异常类型
    print(e)
else:
    print(lsm)
>>>3.0

(2)

try:
    lsm=6/0
except(ZeroDivisionError,NameError) as e:#指定捕获的异常类型
    print(e)
else:
    print(lsm)
>>>division by zero

(3)可以多个except分别处理多个异常

try:
    lsm=6/c
except(ZeroDivisionError) as e:#指定捕获的异常类型
    print(e)
except(NameError) as n:#指定捕获的异常类型
    print(n)
else:
    print(lsm)
>>>name 'c' is not defined

3、finally无论程序是否有异常，都会执行的部分
（1）

try:
    lsm=6/c
except(ZeroDivisionError) as e:#指定捕获的异常类型
    print(e)
except(NameError) as n:#指定捕获的异常类型
    print(n)
else:
    print(lsm)
finally:
    print("i'm finally")
>>>name 'c' is not defined
>>>i'm finally

(2)

try:
    lsm=6/2
except(ZeroDivisionError) as e:#指定捕获的异常类型
    print(e)
except(NameError) as n:#指定捕获的异常类型
    print(n)
else:
    print(lsm)
finally:
    print("i'm finally")
>>>3.0
>>>i'm finally

三、assert关键字

assert expression, e

try:
    lsm=input('input a string of length greater than 4:')
    assert len(lsm)>=4,'string is short'
except AssertionError:
    print('string is short')
    lsm=lsm+"_"*(4-len(lsm))
finally:
    print(lsm)
>>>input a string of length greater than 4:lsm
>>>string is short
>>>lsm_

三、raise关键字，主动抛出异常

raise ValueError( ' This isa value error !' )