class Test(object):
    def __init__(self,name,flag):
        self.filename = name
        self.flag = flag
    
    def __enter__(self):
        ‘‘‘
        @summary: 使用with语句是调用，会话管理器在代码块开始前调用，返回值与as后的参数绑定
        ‘‘‘
        print "__enter__:Open %s"%self.filename
        self.f = open(self.filename,self.flag)
        return self.f
        
    def __exit__(self,Type, value, traceback):
        ‘‘‘
        @summary: 会话管理器在代码块执行完成好后调用（不同于__del__）(必须是4个参数)
        ‘‘‘
        print "__exit__:Close %s"%self.filename
        self.f.close()
        
    def __del__(self):
        print "__del__"
        
if __name__ == "__main__":
    with Test(‘test.txt‘,‘r+‘) as f:
        content = f.read()
        print content
    print "end"