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:
          if train:
              retval = preprocessor_choices.get_class(
                  args.preprocessor
              )(
                  spk2utt=args.spk2utt,
                  train=train,
                  **args.preprocessor_conf,
              )
          else:
              retval = preprocessor_choices.get_class(
                  args.preprocessor
              )(
                  train=train,
                  **args.preprocessor_conf,
              )
  
      else:
          retval = None
      assert check_return_type(retval)
      return retval
  
imports: import argparse
  from typing import Callable, Collection, Dict, List, Optional, Tuple
  import numpy
  import torch
  from typeguard import check_argument_types, check_return_type
  from espnet2.asr.encoder.abs_encoder import AbsEncoder
  from espnet2.asr.frontend.abs_frontend import AbsFrontend
  from espnet2.asr.frontend.asteroid_frontend import AsteroidFrontend
  from espnet2.asr.frontend.default import DefaultFrontend
  from espnet2.asr.frontend.fused import FusedFrontends
  from espnet2.asr.frontend.melspec_torch import MelSpectrogramTorch
  from espnet2.asr.frontend.s3prl import S3prlFrontend
  from espnet2.asr.frontend.windowing import SlidingWindow
  from espnet2.asr.specaug.abs_specaug import AbsSpecAug
  from espnet2.asr.specaug.specaug import SpecAug
  from espnet2.layers.abs_normalize import AbsNormalize
  from espnet2.layers.global_mvn import GlobalMVN
  from espnet2.layers.utterance_mvn import UtteranceMVN
  from espnet2.spk.encoder.ecapa_tdnn_encoder import EcapaTdnnEncoder
  from espnet2.spk.encoder.rawnet3_encoder import RawNet3Encoder
  from espnet2.spk.espnet_model import ESPnetSpeakerModel
  from espnet2.spk.loss.aamsoftmax import AAMSoftmax
  from espnet2.spk.loss.aamsoftmax_subcenter_intertopk import ArcMarginProduct_intertopk_subcenter
  from espnet2.spk.loss.abs_loss import AbsLoss
  from espnet2.spk.pooling.abs_pooling import AbsPooling
  from espnet2.spk.pooling.chn_attn_stat_pooling import ChnAttnStatPooling
  from espnet2.spk.projector.abs_projector import AbsProjector
  from espnet2.spk.projector.rawnet3_projector import RawNet3Projector
  from espnet2.tasks.abs_task import AbsTask
  from espnet2.torch_utils.initialize import initialize
  from espnet2.train.class_choices import ClassChoices
  from espnet2.train.collate_fn import CommonCollateFn
  from espnet2.train.preprocessor import AbsPreprocessor, CommonPreprocessor, SpkPreprocessor
  from espnet2.train.spk_trainer import SpkTrainer
  from espnet2.utils.get_default_kwargs import get_default_kwargs
  from espnet2.utils.nested_dict_action import NestedDictAction
  from espnet2.utils.types import int_or_none, str2bool, str_or_none
label_desc: Use image node_id 3 for calling the SpeakerTask obj's underlying member method code with example usage: obj.build_preprocess_fn(cls, args, train) and returns: retval