code: def save_binary(self, filename):
          
          _safe_call(_LIB.LGBM_DatasetSaveBinary(
              self.construct().handle,
              c_str(filename)))
          return self
docs: Save Dataset to a binary file.
  
          Parameters
          ----------
          filename : string
              Name of the output file.
  
          Returns
          -------
          self : Dataset
              Returns self.