异常处理

import traceback
try:
    ...
except IndexError as e:  # 根据不同的类型，进行处理，这里是记录日志
    logger.info(e)
except TypeError as e:
    traceback.print_exc()  # 这里是输出堆栈的信息
    retrun e
except Exception as e:
    print(e)
else:
    print(‘没有执行except才会执行else里面的内容‘)
finally:
    print(‘无论如何也会执行finally里面的内容‘)

# try-finally示例
try:
    fh = open("c:\testfile", "r")
    try:
        content = fh.read()
        print(content)
    finally:
        print("关闭文件")
        fh.close()
except IOError:
    print("Error: 没有找到文件或读取文件失败")

案例1
class MyException(Exception):                   #让MyException类继承Exception
    def __init__(self,name,age):
        self.name = name
        self.age = age
try:
    #知识点：主动抛出异常，就是实例化一个异常类
    raise MyException("zhansgan",19)            #实例化一个异常,实例化的时候需要传参数
except MyException as obj:                      #这里体现一个封装，
    print(obj.age,obj.name)                     #捕获的就是MyException类携带过来的信息
 
except Exception as obj:                        #万能捕获，之前的可能捕获不到，这里添加Exception作为
    print(obj)                                                                        # 保底
    
案例2
class CustomError(Exception):
    def __init__(self,ErrorInfo):
        super().__init__() #初始化父类
        self.errorinfo=ErrorInfo
    def __str__(self):
        return self.errorinfo

if __name__ == ‘__main__‘:
    try:
        raise CustomError(‘客户异常‘)
    except CustomError as e:
        print(e)    

自定义/with异常

class opened(object):
    def __init__(self, filename):
        self.handle = open(filename)
        print(‘Resource: %s‘ % filename)
        
    def __enter__(self):
        print(‘[Enter %s]: Allocate resource.‘ % self.handle)
        return self.handle  # 可以返回不同的对象
    
    def __exit__(self, exc_type, exc_value, exc_trackback):
        print(‘[Exit %s]: Free resource.‘ % self.handle)
        if exc_trackback is None:
            print(‘[Exit %s]: Exited without exception.,‘ % self.handle)
            self.handle.close()
        else:
            print("error occur!")  # 句柄泄漏
        #return True
        return False  # 会抛出异常，中断程序的执行
    
    
with opened(r‘e:\xx.txt‘) as fp:
    for line in fp.readlines():
        print(line)
    raise TypeError
print("Dnoe")