Python: UserDict
<p>I was reading "Diving into Python". And I ran into this piece of code:</p>

<pre><code>    class UserDict:
        def __init__(self, dict=None):
            self.data = {}
            if dict is not None: self.update(dict)
</code></pre>

<p>Question: why is it "self.update" instead of "self.data.update"?</p>
