class_docstr: Clean examples according to rules
docstr: Get opt string of a `corpus`.
docstr_tok: ["Get","opt","string","of","a","`","corpus","`","."]
code: def _get_opt(corpus, opt, def_val):
      """Get opt string of a `corpus`."""
      if "clean" in corpus["transforms"]:
          value = corpus.get(opt, def_val)
          clean = value
      else:
          clean = None
      return clean
  
file_path: OpenNMT-py/onmt/transforms/clean.py
imports: from onmt.transforms import register_transform
  from .transform import Transform
  from onmt.utils.logging import logger
  import fasttext
  import os
  import urllib.request
  import regex
label_desc: Use image node_id 4 for calling the CleanTransform obj's underlying member method code with example usage: obj._get_opt(corpus, opt, def_val) and returns: clean