Python 中的 With

在 Python 中,与文件相关的操作涉及到读写,经常需要用到 open 和 close,文件打开后,然后关闭,但是 with 的使用可以很好的规避 close。


with open('file_path', 'w') as file: 
    file.write('hello world !') 

同样,在有相关需求的场景中,我们也可以自行构建支持 with 的对象,可以通过定义 enterexit 的方式,如:

# a simple file writer object 
class MessageWriter(object): 
    def __init__(self, file_name): 
        self.file_name = file_name 
    def __enter__(self): 
        self.file = open(self.file_name, 'w') 
        return self.file
    def __exit__(self): 
# using with statement with MessageWriter 
with MessageWriter('my_file.txt') as xfile: 
    xfile.write('hello world')

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