Python 异常处理

一、异常基础

　　1、在编程过程中为了增加友好性，在程序出现bug时一般不会将错误信息显示给用户，而是显示一个提示的页面，通俗来说就是不让用户看见大黄页。

try:
    num1 = input("num1:")
    num2 = input("num2:")
    num1 = int(num1)
    num2 = int(num2)
    reslut = num1 + num2
#先尽量捕获已知的异常最后再捕获万能异常
except ValueError as e:
    print("value err",e)
except IndexError as e:
    print("index err:",e)
except Exception as e:
    print("异常情况如下：",e)

二、自定义异常

class PresleyException(Exception):
    def __init__(self,msg):
        self.message = msg
    def __str__(self):
        return self.message
try:
    raise PresleyException("我的异常")
except PresleyException as e:
    print(e)

三、断言

class PresleyException(Exception):
    def __init__(self,msg):
        self.message = msg
    def __str__(self):
        return self.message

a = 1
try:
    #assert 断言
    #assert a == 1 #如果a == 1那么就过了,因为a=1所以过

    assert a == 2 #因为a =1所以不过，然后走到异常
    #raise PresleyException("我的异常")
except PresleyException as e:
    print(e)

四、finally

class PresleyException(Exception):
    def __init__(self,msg):
        self.message = msg
    def __str__(self):
        return self.message

a = 1
try:
    #assert 断言
    #assert a == 1 #如果a == 1那么就过了,因为a=1所以过
    assert a == 2 #因为a =1所以不过，然后走到异常
    #raise PresleyException("我的异常")
except PresleyException as e:
    print(e)
finally: #无论前面怎么样都执行此下面的步骤
    print("no matter right or wrong,run this anyway")

五、else

#!/usr/bin/python
# -*- coding : utf-8 -*-
# 作者： Presley
# 时间： 2018-11-12
# 邮箱：1209989516@qq.com
# 这是我用来练习异常的测试脚本

class PresleyException(Exception):
    def __init__(self,msg):
        self.message = msg
    def __str__(self):
        return self.message

a = 1
try:
    #assert 断言
    assert a == 1 #如果a == 1那么就过了,因为a=1所以过
    #assert a == 2 #因为a =1所以不过，然后走到异常
    #raise PresleyException("我的异常")
except PresleyException as e:
    print(e)
else:
    print("没有异常")
finally: #无论前面怎么样都执行此下面的步骤
    print("no matter right or wrong,run this anyway")