class_docstr: Abstract class for building a vocabulary from a dataset.
class_docstr_tok: ["Abstract","class","for","building","a","vocabulary","from","a","dataset","."]
docstr: Dump vocabulary to the specified file.
  
  Parameters
  ----------
  fname: str
      A json file fname to save vocabulary.
docstr_tok: ["Dump","vocabulary","to","the","specified","file",".","Parameters","--","--","--","--","--","fname",":","str","A","json","file","fname","to","save","vocabulary","."]
code: def save(self, fname: str):
      """Dump vocabulary to the specified file.
  
      Parameters
      ----------
      fname: str
          A json file fname to save vocabulary.
      """
      raise NotImplementedError()
  
imports: from deepchem.data import Dataset
label_desc: Use image node_id 3 for calling the VocabularyBuilder obj's underlying member method code with example usage: obj.save(fname) without return types