def update_subchunks(self):
        """Auto-updates the existing subchunks data using the 'destination' one."""
        for y in range(16):
            sub = self.destination[:, :, y * 16:16 + (y * 16)]
            if self.destination[:, :, y * 16:].any() or self.binary_data[y] is not None or y in self.subchunks:
                self.binary_data[y] = sub
                if y not in self.subchunks:
                    self.subchunks.append(y)
        self.subchunks.sort()
Auto-updates the existing subchunks data using the 'destination' one.
pymclevel/leveldbpocket.py