Pass list to function by value
<p>I want to pass a list into function by value.
By default, lists and other complex objects passed to function by reference.
Here is some desision:</p>

<pre><code>def add_at_rank(ad, rank):
    result_ = copy.copy(ad)
    .. do something with result_
    return result_
</code></pre>

<p>Can this be written shorter?
In other words, I wanna not to change <strong>ad</strong>.</p>
