code: def bpe_factory(opt: Opt, shared: TShared) -> "BPEHelper":
      """
      BPE Helper Factory.
  
      Returns the appropriate BPE helper given the opt
      as well as available libraries.
  
      :param opt:
          options
      :param shared:
          shared dict
  
      :return BPEHelper:
          returns the appropriate BPEHelper object
      """
      from parlai.core.dict import DictionaryAgent
  
      tokenizer = opt.get("dict_tokenizer", DictionaryAgent.default_tok)
  
      bpe_helper: Optional[BPEHelper] = None
  
      if tokenizer == "bytelevelbpe":
          # Attempt to instantiate HF tokenizer
          try:
              bpe_helper = HuggingFaceBpeHelper(opt, shared)
          except ImportError:
              if opt["dict_loaded"]:
                  warn_once(
                      ""
                      "\n\n--------------------------------------------------\n\n"
                      "WARNING: You have chosen to use Huggingface's tokenizer.\n"
                      "Please install HuggingFace tokenizer with: pip install tokenizers.\n"
                      "For now, defaulting to the GPT2Tokenizer."
                      "\n\n--------------------------------------------------\n\n"
                  )
                  tokenizer = "slow_bytelevel_bpe"
              else:
                  raise ImportError(
                      "Please install HuggingFace tokenizer with: pip install tokenizers.\n"
                  )
      if tokenizer == "slow_bytelevel_bpe":
          bpe_helper = SlowBytelevelBPE(opt, shared)
      if tokenizer == "gpt2":
          bpe_helper = Gpt2BpeHelper(opt, shared)
      if tokenizer == "bpe":
          bpe_helper = SubwordBPEHelper(opt, shared)
  
      assert (
          bpe_helper is not None
      ), f"bpe_factory called with invalid tokenizer: {tokenizer}"
  
      return bpe_helper
  
imports: from parlai.core.params import ParlaiParser
  from abc import ABC, abstractmethod
  from functools import lru_cache
  import json
  import os
  import random
  import re
  from typing import Dict, List, Optional, Set, Tuple
  from typing_extensions import final
  from parlai.core.build_data import download, make_dir
  from parlai.core.opt import Opt
  from parlai.utils.misc import warn_once
  from parlai.utils.typing import TShared
  from parlai.utils.io import PathManager
  import parlai.utils.logging
label_desc: Use image node_id 1 for calling a global function with example usage: bpe_factory(opt, shared) and returns: bpe_helper