title: How to achieve the functionality of UserDict.DictMixin in Python 3?
body: <p>In Python 3 the <code>UserDict.DictMixin</code> class was moved to the <code>collections</code> module. The docs suggest using <code>collections.MutableMapping</code> in its place, however this abstract class does not provide a number of the methods that the <code>DictMixin</code> does/did.</p>
  
  <p>Is there another (or better) way to define them short of grabbing a private copy of the <code>UserDict.Mixin</code> source for importing — or perhaps just copying the needed portions of it — into my own dictionary-like class?</p>