def set_block(self, x,y,z, id, data=0):
        """Sets the block a x, y, z to the specified id, and optionally data."""
        offset = y + z*128 + x*128*16
        self.blocksList[offset] = id
        if (offset % 2 == 1):
            # offset is odd
            index = (offset-1)//2
            b = self.dataList[index]
            self.dataList[index] = (b & 240) + (data & 15) # modify lower bits, leaving higher bits in place
        else:
            # offset is even
            index = offset//2
            b = self.dataList[index]
            self.dataList[index] = (b & 15) + (data << 4 & 240)
Sets the block a x, y, z to the specified id, and optionally data.