class_docstr: Bert-base Model preprocessor.
class_docstr_tok: ["Bert-base","Model","preprocessor","."]
docstr: Prepare needed process units.
docstr_tok: ["Prepare","needed","process","units","."]
code: def _default_units(cls) -> list:
      """Prepare needed process units."""
      return [units.BertClean(), units.BasicTokenize()]
  
file_path: MatchZoo/matchzoo/preprocessors/bert_preprocessor.py
imports: from tqdm import tqdm
  from .None import units
  from .chain_transform import chain_transform
  from matchzoo import DataPack
  from matchzoo.engine.base_preprocessor import BasePreprocessor
  from .build_vocab_unit import built_bert_vocab_unit
  from .build_unit_from_data_pack import build_unit_from_data_pack
label_desc: Use image node_id 4 for calling the BertPreprocessor obj's underlying member method code with example usage: obj._default_units(cls) and returns: list