异常处理
在日常编程中我们经常会遇见很多BUG，总的来说bug分为两大类：语法错误跟逻辑错误
语法错误在程序启动就会报出，所以这种错误很容易被发现，容易改正。
今天要讲的是程序中的各种逻辑错误，这种错误不易被发现。
1、什么是异常
异常是错误发生的信号，
程序一旦出错，如果程序中还没有相应的处理机制
那么该错误就会产生一个异常抛出来
程序的运行也随之终止
2、一个异常分为三部分：
1、异常的追踪信息
2、异常的类型
3、异常的值
3、异常的分类：
1、语法异常：
这类异常应该在程序执行前就改正
print('start....')
x=1
x+=1
if
print('stop....')
2、逻辑上的异常
# IndexError # l=['a','b'] # l[100] # KeyError # d={'a':1} # d['b'] # AttributeError: # class Foo: # pass # # Foo.x # import os # os.aaa # ZeroDivisionError # 1 / 0 # FileNotFoundError # f=open('a.txt','r',encoding='utf-8') # ValueError: I/O operation on closed file. # f=open('a.txt','r',encoding='utf-8') # f.close() # f.readline() #ValueError: invalid literal for int() with base 10: 'aaaaa' # int('aaaaa') # TypeError # for i in 333: # pass #NameError # x # func() # def func(): # import os # os.xxxx # # func()
# 语法：
# 单分支
# try:
# print('start.....')
# x=1
# y
# l=[]
# l[3]
# d={'a':1}
# d['b']
# print('end....')
# except NameError:
# print('变量名没有定义')
#
#
# print('other.....')
# 多分支
# try:
# print('start.....')
# x=1
# # y
# l=[]
# l[3]
# d={'a':1}
# d['b']
# print('end....')
# except NameError:
# print('变量名没有定义')
# except KeyError:
# print('字典的key不存在')
# except IndexError:
# print('索引超出列表的范围')
#
#
# print('other.....')
# 多种异常采用同一段逻辑处理
# try:
# print('start.....')
# x=1
# # y
# l=[]
# # l[3]
# d={'a':1}
# d['b']
# print('end....')
# except (NameError,KeyError,IndexError):
# print('变量名或者字典的key或者列表的索引有问题')
# print('other.....')
# 万能异常
# try:
# print('start.....')
# x=1
# # y
# l=[]
# # l[3]
# d={'a':1}
# # d['b']
# import os
# os.aaa
# print('end....')
# except Exception:
# print('万能异常---》')
#
#
# print('other.....')
# 获取异常的值
# try:
# print('start.....')
# x=1
# y
# l=[]
# l[3]
# d={'a':1}
# d['b']
# import os
# os.aaa
# print('end....')
# except Exception as e:
# print('万能异常---》',e)
#
#
# print('other.....')
# try:
# print('start.....')
# x=1
# # y
# l=[]
# l[3]
# d={'a':1}
# d['b']
# import os
# os.aaa
# print('end....')
# except NameError as e:
# print('NameError: ',e)
#
# except KeyError as e:
# print('KeyError: ',e)
#
# except Exception as e:
# print('万能异常---》',e)
#
#
# print('other.....')
# try....else...
# else: 不能单独使用，必须与except连用，意思是：else的子代码块会在被检测的代码没有出现过任何异常的情况下执行
# try:
# print('start.....')
# # x=1
# # # y
# # l=[]
# # l[3]
# # d={'a':1}
# # d['b']
# # import os
# # os.aaa
# print('end....')
# except NameError as e:
# print('NameError: ',e)
#
# except KeyError as e:
# print('KeyError: ',e)
#
# except Exception as e:
# print('万能异常---》',e)
#
# else:
# print('在被检测的代码块没有出现任何异常的情况下执行')
# print('other.....')
# try...finally....
# try:
# print('start.....')
# # x=1
# # # y
# # l=[]
# # l[3]
# # d={'a':1}
# # d['b']
# # import os
# # os.aaa
# print('end....')
# except NameError as e:
# print('NameError: ',e)
#
# except KeyError as e:
# print('KeyError: ',e)
#
# except Exception as e:
# print('万能异常---》',e)
#
# else:
# print('在被检测的代码块没有出现任何异常的情况下执行')
# finally:
# print('无论有没有异常发生，都会执行')
# print('other.....')
# finally的子代码块中通常放回收系统资源的代码
# try:
# f=open('a.txt',mode='w',encoding='utf-8')
# f.readline()
#
# finally:
# f.close()
#
# print('other....')
# 主动触发异常
# raise TypeError('类型错误')
# class People:
# def __init__(self,name):
# if not isinstance(name,str):
# raise TypeError('%s 必须是str类型' %name)
#
# self.name=name
#
# p=People(123)
# 断言
# print('part1........')
# # stus=['egon','alex','wxx','lxx']
# stus=[]
#
#
# # if len(stus) <= 0:
# # raise TypeError
# assert len(stus) > 0
#
# print('part2.........')
# print('part2.........')
# print('part2.........')
# print('part2.........')
# print('part2.........')
# print('part2.........')
# 自定义异常
# class RegisterError(BaseException):
# def __init__(self,msg,user):
# self.msg=msg
# self.user=user
#
# def __str__(self):
# return '<%s：%s>' %(self.user,self.msg)
#
# raise RegisterError('注册失败','teacher')
