Rounded Dictionary Access in Python

roundingdict.py

class RoundingDict(dict):
    def __getitem__(self, key):
        if key in self:
            return dict.__getitem__(self, key)
        try:
            values = [abs(x - key) for x in self.keys()]
            return self.values()[values.index(min(values))]
        except (TypeError, ValueError):
            raise KeyError(key)

if __name__ == "__main__":
    # Useful for storing sparse numeric lookup tables
    x = RoundingDict({5: "Some low value...", 50: "Middle of the road.", 100: "Top end!"})
    
    print "What's 22?"
    print x[22]

    print "What about 78?"
    print x[78]

    # Or, in my case, for storing audio samples:
    velocity_map = RoundingDict({0: "snare_soft.wav", 64: "snare_med.wav", 127: "snare_loud.wav"})
    
    print "What samples should I use for a snare roll?"
    for velocity in xrange(0, 127, 10):
        print velocity_map[velocity]