python:好用的 with 语法

手动清理资源占用是个很痛苦的事情，比如刚学编程时候，老鸟就建议：写完open xxx 之后一定要写一个配对儿的 close，然后再往他俩中间写逻辑。

python 现在有个好玩的东西，利用上下文可以自动释放掉一个对象：

class test(): def __init__(self,msg): print(msg) def __enter__(self): print('Enter Object test') def __exit__(self, exc_type, exc_val, exc_tb): print('Exit Object test') object=test('Hello') print('***head of code block***') with object as t: print('Did something here...') print('***end of code block***') 

运行结果如下：

Hello ***head of code block*** Enter Object test Did something here... Exit Object test ***end of code block*** Process finished with exit code 0

于是，对于系统自带的文件操作就有了下面这样的用法：

content='' with open('test.txt','a',encoding='UTF-8') as f: f.write('Hello World\n') with open('test.txt','r',encoding='UTF-8') as f: content=f.read() print(content)

*注意两个f不是同一个对象

是不是很爽？几下就搞定了O(∩_∩)O