def discardChunk(self, cx, cz):
        " discards the chunk renderer for this chunk and compresses the chunk "
        if (cx, cz) in self.chunkRenderers:
            self.bufferUsage -= self.chunkRenderers[cx, cz].bufferSize
            self.chunkRenderers[cx, cz].forgetDisplayLists()
            del self.chunkRenderers[cx, cz]
 discards the chunk renderer for this chunk and compresses the chunk 
renderer.py