异常处理

一:何为异常处理

 

 1.异常是错误发生的信号,一旦程序出错就会产生一个异常,如果该异常没有被应用程序

处理,那么该异常就会抛出来,程序的执行页随之中止

异常包含三个部分:

　　1 traceback异常的追踪信息

　　2 异常的类型

　　3 异常的信息

错误被分为两大类:

　　1 语法上的错误:子啊程序运行前就应该立即修正

　　2 逻辑上的错误

2 .为何要异常处理

　　避免程序因为异常而崩溃,所以在应用程序中应该对一场进行处理,从而增强程序的健壮性

3 怎么异常处理

try:

　　code1

　　code2

　　code3

except NameError:

　　当抛出的异常是NameError时执行的子代码块

except...:

　　pass

except...:
　　pass

else:

　　pass

finally:

　　pass

# 1. 常见的逻辑错误导致的异常
# print('adsfsadf'

# age=input('>>: ').strip()
# print(age > 10) #TypeError

# for i in 10: #TypeError
#     pass

# import os
# os.xxx #AttributeError

# 1 / 0 #ZeroDivisionError:

# print('=====1')
# print('=====2')
# print('=====3')
# l=[1,2,3]
# l[1000] #IndexError
# print('=====4')
# d={'x':1,'y':2}
# d['z'] #KeyError
# print('=====5')

# 2. 异常处理

# 异常处理的单分支
# try:
#     print('=====1')
#     print('=====2')
#     print('=====3')
#     d = {'x': 1, 'y': 2}
#     d['z']  # KeyError
#     print('=====4')
#     l = [1, 2, 3]
#     l[1000]  # IndexError
#     print('=====5')
# except IndexError:
#     print('IndexError')
#
# print('other code')

# 异常处理的多分支
# try:
#     print('=====1')
#     print('=====2')
#     print('=====3')
#     d = {'x': 1, 'y': 2}
#     d['z']  # KeyError
#     print('=====4')
#     l = [1, 2, 3]
#     l[1000]  # IndexError
#     print('=====5')
# except KeyError as e:
#     print('KeyError',e)
# except IndexError as e:
#     print('IndexError',e)
#
#
# print('other code')




# try:
#     print('=====1')
#     print('=====2')
#     print('=====3')
#     d = {'x': 1, 'y': 2}
#     # d['z']  # KeyError
#     print('=====4')
#     l = [1, 2, 3]
#     l[1000]  # IndexError
#     print('=====5')
# except (KeyError,IndexError) as e:
#     print(e)
# print('other code')

# 万能异常类型Exception:可以匹配任意类型的异常
# try:
#     print('=====1')
#     print('=====2')
#     print('=====3')
#     d = {'x': 1, 'y': 2}
#     # d['z']  # KeyError
#     # xxx
#     print('=====4')
#     l = [1, 2, 3]
#     l[1000]  # IndexError
#     print('=====5')
# except IndexError as e:
#     print('IndexError:', e)
# except KeyError as e:
#     print('KeyError:', e)
# except Exception as e:
#     print('Exception:',e)
#
# print('other code')

# try... else...
# try:
#     print('=====1')
#     print('=====2')
#     print('=====3')
#     d = {'x': 1, 'y': 2}
#     # d['z']  # KeyError
#     # xxx
#     print('=====4')
#     l = [1, 2, 3]
#     # l[1000]  # IndexError
#     print('=====5')
# except IndexError as e:
#     print('IndexError:', e)
# except KeyError as e:
#     print('KeyError:', e)
# except Exception as e:
#     print('Exception:',e)
# else:
#     print('else必须放到后面,else的子代码块会在被检测的代码没有异常的情况下执行')
# # print('other code')

# try... finally...
# try:
#     f=open('a.txt','w')
#     print('=====1')
#     print('=====2')
#     print('=====3')
#     d = {'x': 1, 'y': 2}
#     # d['z']  # KeyError
#     # xxx
#     'xx' > 10
#     print('=====4')
#     l = [1, 2, 3]
#     # l[1000]  # IndexError
#     print('=====5')
#
# except IndexError as e:
#     print('IndexError:', e)
# except KeyError as e:
#     print('KeyError:', e)
# # except Exception as e:
# #     print('Exception:',e)
# else:
#     print('else必须放到后面,else的子代码块会在被检测的代码没有异常的情况下执行')
# finally:
#     print('无论被检测的代码有没有异常都会执行')
#     f.close()


# 主动触发异常
# print('===>1')
# print('===>2')
# raise TypeError('类型错误')
# print('===>3')

# class People:
#     def __init__(self,name,age):
#         self.__name=name
#         self.__age=age
#
#     def tell_info(self):
#         print(self.__name,self.__age)
#
#     def set_info(self,name,age):
#         if not isinstance(name,str):
#             raise TypeError('名字必须是str类型')
#         if not isinstance(age,int):
#             raise TypeError('年龄必须是int类型')
#         self.__name=name
#         self.__age=age
#
# obj=People('egon',18)
# # print(obj.__dict__)
# # obj.tell_info()
#
# obj.set_info('egon',123)
# obj.tell_info()
#


# 自定义异常类型(了解)
# class MyException(BaseException):
#     def __init__(self,msg):
#         super().__init__()
#         self.msg=msg
#
#     def __str__(self):
#         return '<%s>' %self.msg
#
# raise MyException('我自定义的异常')



# 断言(了解)
print('上半部分,生产数据')
l=[1,2,3,4]

# if len(l) != 5:
#     raise TypeError('列表的长度必须为5')
assert len(l) == 5

print('下半部分,处理数据')