我在 python/Lib 源代码中看到了很多，但我不知道它是干什么用的.
I've seen it a lot in python/Lib source code but I don't know what it is for.
我认为它用于限制模块的可访问成员.所以只有 __all__ 处的元素会在 dir(module) 时出现.
I thought it was used to limit accessible members of of a module. So only the elements at __all__ will show up when dir(module).
我做了一个小例子，发现它没有按预期工作.
I did a little example and saw it was not working as I expected.
那么... python __all__ 模块级变量是干什么用的?
So... What's the python __all__ module level variable for?
它有两个目的:
任何阅读源代码的人都会知道公开的公共 API 是什么.它不会阻止他们在私有声明中四处寻找，但确实提供了一个很好的警告.
Anybody who reads the source will know what the exposed public API is. It doesn't prevent them from poking around in private declarations, but does provide a good warning not to.
使用 from mod import * 时，只会导入 __all__ 中列出的名称.在我看来，这并不重要，因为导入所有内容真的是个坏主意.
When using from mod import *, only names listed in __all__ will be imported. This is not as important, in my opinion, because importing everything is a really bad idea.
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