'Returns all entites that have had new things since the given
position. If the position is too old it will return None.'

def get_all_entities_changed(self, stream_pos):

    assert (type(stream_pos) is int)
    if (stream_pos >= self._earliest_known_stream_pos):
        keys = self._cache.keys()
        i = keys.bisect_right(stream_pos)
        return [self._cache[k] for k in keys[i:]]
    else:
        return None
