code: def _get_tokenizer(self, tokenizer_name: str) -> Tokenizer:
      if tokenizer_name not in self.VALID_TOKENIZERS:
          raise ValueError(f"Invalid tokenizer: {tokenizer_name}")
  
      # Check if the tokenizer is cached
      if tokenizer_name not in self._tokenizer_name_to_tokenizer:
          self._tokenizer_name_to_tokenizer[
              tokenizer_name
          ] = self._aleph_alpha_client.tokenizer(tokenizer_name)
          hlog(f"Initialized tokenizer: {tokenizer_name}")
      return self._tokenizer_name_to_tokenizer[tokenizer_name]
  
file_path: H2O/h2o_hf/helm/src/helm/proxy/clients/aleph_alpha_client.py
imports: import json
  import requests
  from typing import Any, Dict, List
  from aleph_alpha_client import Client
  from tokenizers import Tokenizer, Encoding
  from helm.common.cache import Cache, CacheConfig
  from helm.common.hierarchical_logger import hlog
  from helm.common.request import Request, RequestResult, Sequence, Token
  from helm.common.tokenization_request import DecodeRequest, DecodeRequestResult, TokenizationRequest, TokenizationRequestResult, TokenizationToken
  from .client import Client, wrap_request_time, truncate_sequence
label_desc: Use image node_id 2 for calling the AlephAlphaClient obj's underlying member method code with example usage: obj._get_tokenizer(tokenizer_name) and returns: self