What's the python __all__ module level variable for?
<p>I've seen it a lot in python/Lib source code but I don't know what it is for.</p>

<p>I thought it was used to limit accessible members of of a module. So only the elements at <code>__all__</code> will show up when <code>dir(module)</code>.</p>

<p>I did a little example and saw it was not working as I expected.</p>

<p>So... What's the python <code>__all__</code> module level variable for?</p>
