code: def source_dictionary(self) -> Optional[Dictionary]:
      return self._source_dictionary
  
imports: import logging
  import sys
  import torch
  from dataclasses import dataclass, field
  from typing import List, Optional, Tuple
  from fairseq.data import Dictionary
  from fairseq.data.codedataset import ExpressiveCodeDataConfig, CodeDataset
  from fairseq.dataclass.configs import FairseqDataclass
  from fairseq.tasks import register_task
  from fairseq.tasks.fairseq_task import FairseqTask
  from omegaconf import MISSING, DictConfig
label_desc: Use image node_id 2 for calling the SpeechUnitLanguageModelingTask obj's underlying member method code with example usage: obj.source_dictionary() and returns: self