class_docstr: DSSM 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.Tokenize(),
          units.Lowercase(),
          units.PuncRemoval(),
          units.StopRemoval(),
          units.NgramLetter(),
      ]
  
file_path: MatchZoo/matchzoo/preprocessors/dssm_preprocessor.py
imports: from tqdm import tqdm
  from matchzoo.data_pack import DataPack
  from matchzoo.engine.base_preprocessor import BasePreprocessor
  from .chain_transform import chain_transform
  from .build_vocab_unit import build_vocab_unit
  from .None import units
label_desc: Use image node_id 4 for calling the DSSMPreprocessor obj's underlying member method code with example usage: obj._default_units(cls) and returns: list