class_docstr: analogous to fairseq.data.IndexedCachedDataset
code: def save(self, path):
      assert self.word_buffer is not None
      assert self.word_offsets is not None
      assert self.char_buffer is not None
      assert self.char_offsets is not None
      with PathManager.open(path, "wb") as f:
          np.savez(
              f,
              word_buffer=self.word_buffer,
              word_offsets=self.word_offsets,
              char_buffer=self.char_buffer,
              char_offsets=self.char_offsets,
          )
  
imports: from typing import Any, Dict
  import numpy
  import torch
  from fairseq import data, tokenizer
  from fvcore.common.file_io import PathManager
  from pytorch_translate import vocab_constants
  from pytorch_translate.data.dictionary import TAGS
label_desc: Use image node_id 6 for calling the InMemoryNumpyWordCharDataset obj's underlying member method code with example usage: obj.save(path) without return types