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POHow to "perfectly" override a dict?
 

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  1. POHow to "perfectly" override a dict?
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    <p>How can I make as "perfect" a subclass of <em>dict</em> as possible? The end goal is to have a simple <em>dict</em> in which the keys are lowercase.</p> <p>It would seem that there should be some tiny set of primitives I can override to make this work, but according to all my research and attempts it seem like this isn't the case:</p> <ul> <li><p>If I <a href="https://stackoverflow.com/a/2390889">override <code>__getitem__</code>/<code>__setitem__</code></a>, then <code>get</code>/<code>set</code> don't work. How can I make them work? Surely I don't need to implement them individually?</p></li> <li><p>Am I preventing pickling from working, and do I need to implement <code>__setstate__</code> etc?</p></li> <li><p>Do I <a href="https://stackoverflow.com/a/2390997">need <code>repr</code>, <code>update</code> and <code>__init__</code></a>?</p></li> <li><p>Should I just <a href="https://stackoverflow.com/a/1622872">use mutablemapping</a> (it seems one shouldn't use <code>UserDict</code> or <code>DictMixin</code>)? If so, how? The docs aren't exactly enlightening.</p></li> </ul> <p>Here is my first go at it, <code>get()</code> doesn't work and no doubt there are many other minor problems:</p> <pre><code>class arbitrary_dict(dict): """A dictionary that applies an arbitrary key-altering function before accessing the keys.""" def __keytransform__(self, key): return key # Overridden methods. List from # https://stackoverflow.com/questions/2390827/how-to-properly-subclass-dict def __init__(self, *args, **kwargs): self.update(*args, **kwargs) # Note: I'm using dict directly, since super(dict, self) doesn't work. # I'm not sure why, perhaps dict is not a new-style class. def __getitem__(self, key): return dict.__getitem__(self, self.__keytransform__(key)) def __setitem__(self, key, value): return dict.__setitem__(self, self.__keytransform__(key), value) def __delitem__(self, key): return dict.__delitem__(self, self.__keytransform__(key)) def __contains__(self, key): return dict.__contains__(self, self.__keytransform__(key)) class lcdict(arbitrary_dict): def __keytransform__(self, key): return str(key).lower() </code></pre>
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