Python datatype suitable for my cache
<p>I'm searching for the a datatype for a cache, basically I need the functionality of a dict, i.e. random access based on a key, which has a limited number of entries so that when the limit is reached the oldest item gets automatically removed.
Furthermore I need to be able to store it via shelve or pickle and rely on Python 2.4.
Should I subclass dict and add a list to it? Any suggestions?</p>

<p><strong>Edit:</strong><br />
I have not mentioned the scale, I need to keep track of already read items which consist of a signature by which they are identified and I only want to keep track of about a few hundred of them.
collections.deque seem nice but that's a list and I need random access. So dict would seem suitable, however somehow I need to expire items if the limit is hit which means I need to keep track the order in which they have been added.</p>
