def getChunk(self, cx, cz):
        for p in cx, cz:
            if not 0 <= p <= 31:
                raise ChunkNotPresent((cx, cz, self))

        c = self._loadedChunks.get((cx, cz))
        if c is None:
            c = self.chunkFile.loadChunk(cx, cz, self)
            self._loadedChunks[cx, cz] = c
        return c