code: def nbytes(self):
      return np.prod(self.shape) * self.dtype.itemsize
  
file_path: mars/mars/core/entity/fuse.py
imports: import numpy
  from ...serialization.serializables import ReferenceField
  from .chunks import ChunkData, Chunk, CHUNK_TYPE
label_desc: Use image node_id 6 for calling the FuseChunkData obj's underlying member method code with example usage: obj.nbytes() and returns: unknown