What does this code from types.py do?
<pre><code>try:
    raise TypeError
except TypeError:
    try:
        tb = sys.exc_info()[2]
        TracebackType = type(tb)
        FrameType = type(tb.tb_frame)
    except AttributeError:
        # In the restricted environment, exc_info returns (None, None,
        # None) Then, tb.tb_frame gives an attribute error
        pass
    tb = None; del tb
</code></pre>

<p>I can't understand this code at all. What is it's purpose?</p>
