code: def get_gpt_tokenizer():
      """GPT (BPE) tokenizer."""
      args = get_retro_args()
      tokenizer_type = args.retro_gpt_tokenizer_type
      if tokenizer_type == "GPT2BPETokenizer":
          assert args.retro_gpt_vocab_file and args.retro_gpt_merge_file
          return _GPT2BPETokenizer(
              vocab_file=args.retro_gpt_vocab_file,
              merge_file=args.retro_gpt_merge_file,
          )
      elif tokenizer_type == "GPTSentencePieceTokenizer":
          assert args.retro_gpt_tokenizer_model is not None
          return _GPTSentencePieceTokenizer(
              args.retro_gpt_tokenizer_model
          )
      else:
          raise Exception(
              "unrecognized gpt tokenizer, '%s'." % tokenizer_type
          )
  
file_path: megatron-lm/tools/retro/utils.py
imports: import os
  import torch
  import types
  from megatron import get_retro_args
  from megatron.tokenizer.tokenizer import _BertWordPieceTokenizer, _GPT2BPETokenizer, _GPTSentencePieceTokenizer
label_desc: Use image node_id 3 for calling a global function with example usage: get_gpt_tokenizer() and returns: _GPT2BPETokenizer, _GPTSentencePieceTokenizer