if not hits:
    {}[key]
if len(hits) > 1:
    raise RangeDict.AmbiguityException()
return super().__getitem__(hits[0])
subjects = {(0, 9): 'fail', (9, 15): 'pass', (15, 18): 'merit', (18, 21):
    'Distinction'}
rd = RangeDict(subjects)
for x in range(21):
    pass
3-х мерный словарь