Python高级笔记（八）with、上下文管理器

1. 上下文管理器

__enter__()方法返回资源对象，__exit__()方法处理一些清除资源

如：系统资源：文件、数据库链接、Socket等这些资源执行完业务逻辑之后，必须要关闭资源

#!/usr/bin/python3
#-*- coding:utf-8 -*-

class File(object):

    def __init__(self, filename, mode):
        self.filename = filename
        self.mode = mode
    
    def __enter__(self):
        print("entering....")
        self.f = open(self.filename, self.mode)
        return self.f
    
    def __exit__(self, *args):
        print("will exit")
        self.f.close()

with File("out.txt", 'w') as f:
    print("writing....")
    f.write('hello, python')

entering....
writing....
will exit

2. 使用 @contextmanager

from contextlib import contextmanager

@contextmanager
def my_open(path, mode):
    f = open(path, mode)
    yield f
    f.close()

with my_open('out.txt', 'w') as f:
    f.write("hello, test")