code: def build_preprocess_fn(
      cls, args: argparse.Namespace, train: bool
  ) -> Optional[
      Callable[[str, Dict[str, np.array]], Dict[str, np.ndarray]]
  ]:
      assert check_argument_types()
      if args.use_preprocessor:
          retval = SLUPreprocessor(
              train=train,
              token_type=args.token_type,
              token_list=args.token_list,
              transcript_token_list=None
              if "transcript_token_list" not in args
              else args.transcript_token_list,
              bpemodel=args.bpemodel,
              non_linguistic_symbols=args.non_linguistic_symbols,
              text_cleaner=args.cleaner,
              g2p_type=args.g2p,
              # NOTE(kamo): Check attribute existence for backward compatibility
              rir_scp=getattr(args, "rir_scp", None),
              rir_apply_prob=getattr(args, "rir_apply_prob", 1.0),
              noise_scp=getattr(args, "noise_scp", None),
              noise_apply_prob=getattr(args, "noise_apply_prob", 1.0),
              noise_db_range=getattr(args, "noise_db_range", "13_15"),
              short_noise_thres=getattr(args, "short_noise_thres", 0.5),
              speech_volume_normalize=getattr(args, "rir_scp", None),
              **getattr(args, "preprocessor_conf", {}),
          )
      else:
          retval = None
      assert check_return_type(retval)
      return retval
  
imports: import argparse
  import logging
  from typing import Callable, Dict, Optional, Tuple
  import numpy
  from typeguard import check_argument_types, check_return_type
  from espnet2.asr.ctc import CTC
  from espnet2.asr.decoder.abs_decoder import AbsDecoder
  from espnet2.asr.decoder.mlm_decoder import MLMDecoder
  from espnet2.asr.decoder.rnn_decoder import RNNDecoder
  from espnet2.asr.decoder.transducer_decoder import TransducerDecoder
  from espnet2.asr.decoder.transformer_decoder import DynamicConvolution2DTransformerDecoder, DynamicConvolutionTransformerDecoder, LightweightConvolution2DTransformerDecoder, LightweightConvolutionTransformerDecoder, TransformerDecoder
  from espnet2.asr.encoder.abs_encoder import AbsEncoder
  from espnet2.asr.encoder.branchformer_encoder import BranchformerEncoder
  from espnet2.asr.encoder.conformer_encoder import ConformerEncoder
  from espnet2.asr.encoder.contextual_block_conformer_encoder import ContextualBlockConformerEncoder
  from espnet2.asr.encoder.contextual_block_transformer_encoder import ContextualBlockTransformerEncoder
  from espnet2.asr.encoder.hubert_encoder import FairseqHubertEncoder, FairseqHubertPretrainEncoder
  from espnet2.asr.encoder.longformer_encoder import LongformerEncoder
  from espnet2.asr.encoder.rnn_encoder import RNNEncoder
  from espnet2.asr.encoder.transformer_encoder import TransformerEncoder
  from espnet2.asr.encoder.vgg_rnn_encoder import VGGRNNEncoder
  from espnet2.asr.encoder.wav2vec2_encoder import FairSeqWav2Vec2Encoder
  from espnet2.asr.frontend.abs_frontend import AbsFrontend
  from espnet2.asr.frontend.default import DefaultFrontend
  from espnet2.asr.frontend.fused import FusedFrontends
  from espnet2.asr.frontend.s3prl import S3prlFrontend
  from espnet2.asr.frontend.windowing import SlidingWindow
  from espnet2.asr.postencoder.abs_postencoder import AbsPostEncoder
  from espnet2.asr.postencoder.hugging_face_transformers_postencoder import HuggingFaceTransformersPostEncoder
  from espnet2.asr.preencoder.abs_preencoder import AbsPreEncoder
  from espnet2.asr.preencoder.linear import LinearProjection
  from espnet2.asr.preencoder.sinc import LightweightSincConvs
  from espnet2.asr.specaug.abs_specaug import AbsSpecAug
  from espnet2.asr.specaug.specaug import SpecAug
  from espnet2.asr_transducer.joint_network import JointNetwork
  from espnet2.layers.abs_normalize import AbsNormalize
  from espnet2.layers.global_mvn import GlobalMVN
  from espnet2.layers.utterance_mvn import UtteranceMVN
  from espnet2.slu.espnet_model import ESPnetSLUModel
  from espnet2.slu.postdecoder.abs_postdecoder import AbsPostDecoder
  from espnet2.slu.postdecoder.hugging_face_transformers_postdecoder import HuggingFaceTransformersPostDecoder
  from espnet2.slu.postencoder.conformer_postencoder import ConformerPostEncoder
  from espnet2.slu.postencoder.transformer_postencoder import TransformerPostEncoder
  from espnet2.tasks.asr import ASRTask
  from espnet2.text.phoneme_tokenizer import g2p_choices
  from espnet2.torch_utils.initialize import initialize
  from espnet2.train.abs_espnet_model import AbsESPnetModel
  from espnet2.train.class_choices import ClassChoices
  from espnet2.train.preprocessor import SLUPreprocessor
  from espnet2.train.trainer import Trainer
  from espnet2.utils.get_default_kwargs import get_default_kwargs
  from espnet2.utils.nested_dict_action import NestedDictAction
  from espnet2.utils.types import float_or_none, int_or_none, str2bool, str_or_none
label_desc: Use image node_id 2 for calling the SLUTask obj's underlying member method code with example usage: obj.build_preprocess_fn(cls, args, train) and returns: retval