python 多个with 语句一起使用

在读《流畅的Python》时，偶然看到下面的语句：

with urlopen(URL) as remote, open(JSON, 'wb') as local:
    local.write(remote.read())

突然才发现，原来多个with语句可以写到一起!

我之前都是每个with一个层级，像下面这样：

with open('in_file') as f:
    with open('out_file' 'w') as of:
        for line in f:
            of.write(line)
            ...

这样写每个with语句需要缩进一次，阅读起来逻辑不连续，而且很容易超过每行的字符限制，导致需要换行等问题，不是很方便。

经过这个偶然的发现，以后上面的代码可以这样写了：

with open('in_file') as f, open('out_file' 'w') as of:
    for line in f:
        of.write(line)
        ...

同时看 with 语句的官方文档，发现从Python 3.10版本起，还可以用括号将多个with语句括起来:

with (
    open("face_model_choice.txt") as f,
    open("ttt.txt", "w") as of1,
    open("ttt2.txt", "w") as of2,
):
    for line in f:
        of1.write(line)
        of2.write(line)
		...

这样看起来也更简洁了。