title: OrderedDict for older versions of python
body: <p>Ordered dictionaries are extremely useful structures, but unfortunately these are quite recent only working in versions from <a href="http://docs.python.org/dev/py3k/library/collections.html#ordereddict-objects" rel="noreferrer">3.1</a> and <a href="http://docs.python.org/dev/whatsnew/2.7.html#pep-372-adding-an-ordered-dictionary-to-collections" rel="noreferrer">2.7</a>. How can I use an ordered dictionary in older versions?</p>