Lookup an item in the cache and return an iterator
        that reads chunksize bytes of data at a time.  The underlying
        file will be closed when all data has been read

def load_iter(self, key, chunksize=None, noexpire=None):
        '''Lookup an item in the cache and return an iterator
        that reads chunksize bytes of data at a time.  The underlying
        file will be closed when all data has been read'''
        return chunk_iterator(self.load_fd(key, noexpire=noexpire),
                              chunksize=chunksize)