>>> r = RawBSONDocument(BSON.encode({}))
>>> r['f']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "bson/raw_bson.py", line 77, in __getitem__
    return self.__inflated[item]
KeyError: 'f'

>>> from bson.raw_bson import RawBSONDocument
>>> r = RawBSONDocument(BSON.encode({}))
>>> r['f']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "bson/raw_bson.py", line 83, in __getitem__
    return self.__inflated[item]
  File "bson/raw_bson.py", line 79, in __inflated
    raise InvalidBSON('bad object or element length')
bson.errors.InvalidBSON: bad object or element length