src/transformers/models/auto/tokenization_auto.py/tokenizer_class_from_name
def tokenizer_class_from_name(class_name: str):
    if class_name == "PreTrainedTokenizerFast":
        return PreTrainedTokenizerFast

    for module_name, tokenizers in TOKENIZER_MAPPING_NAMES.items():
        if class_name in tokenizers:
            module_name = model_type_to_module_name(module_name)

            module = importlib.import_module(f".{module_name}", "transformers.models")
            return getattr(module, class_name)

    return None