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')
